Practical Radiation Oncology (2013) 3, e99–e106
www.practicalradonc.org
Original Report
How important is dosimetrist experience for intensity modulated radiation therapy? A comparative analysis of a head and neck case Vikneswary Batumalai MHlthSc a,b,⁎, Michael G. Jameson BMedRadPhys a,c , Dion F. Forstner MD a,d , Philip Vial PhD a,e , Lois C. Holloway PhD a,b,c,e a
Cancer Therapy Centre, Liverpool Hospital, Sydney, Australia University of New South Wales, NSW, Australia c Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia d Collaboration of Cancer Outcome Research and Evaluation (CCORE), Liverpool Hospital, Sydney, Australia e Institute of Medical Physics, School of Medical Physics, University of Sydney, Sydney, Australia b
Received 27 March 2012; revised 4 June 2012; accepted 22 June 2012
Abstract Purpose: Treatment planning for IMRT is a complex process that requires additional training and expertise. The aim of this study was to compare and analyze IMRT plans generated by dosimetrists with varying levels of IMRT planning experience. Methods and Materials: The computed tomography (CT) data of a patient previously treated with IMRT for left tonsillar carcinoma were used. The patient's preexisting planning target volumes (PTVs) and all organs at risk were provided with the CT data set. Six dosimetrists with variable IMRT planning experience generated IMRT plans according to the department's protocol. Plan analysis included visual inspection and comparison of dose-volume histogram, conformity indices, treatment delivery efficiency, and dose delivery accuracy. Results: Visual review of the dose distribution showed that the 6 plans were comparable. However, only the 2 most experienced dosimetrists were able to meet the strict PTV aims and critical structure constraints. The least experienced dosimetrist had the worst planning outcome. Comparison of delivery efficiency showed that the number of segments, total monitor units, and treatment time increased as the IMRT planning experience decreased. Conclusions: Dosimetrists with higher levels of IMRT planning experience produced a better quality head and neck IMRT plan. Different planning experience may need to be considered when organizing appropriate departmental resources. Crown Copyright © 2013 Published by Elsevier Inc. on behalf of American Society for Radiation Oncology. All rights reserved.
Presented at the 11th Biennial Meeting of European Society for Therapeutic Radiology and Oncology (ESTRO), London, UK, May 8-12, 2011. Conflicts of interest: None. ⁎ Corresponding author. Cancer Therapy Centre, Liverpool Hospital, Locked Bag 7103, Liverpool BC, NSW 1871, Australia. E-mail address: [email protected] (V. Batumalai).
Introduction Intensity modulated radiation therapy (IMRT) has become the standard of care for many patients in radiation therapy for a variety of tumor sites. IMRT planning was
1879-8500/$ – see front matter. Crown Copyright © 2013 Published by Elsevier Inc. on behalf of American Society for Radiation Oncology. All rights reserved. http://dx.doi.org/10.1016/j.prro.2012.06.009
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Dosimetrist intensity modulated radiation therapy planning experience based on tumor site
Dosimetrist
Nasopharynx
Tonsil
Nasal cavity
Pharynx
Palate
Glottis
Pyriform sinus
Maxilla
Larynx
A B C D E F
5 3 3 3 2 2
5 4 2 3 3 –
4 2 – – – –
4 6 1 4 3 1
2 3 – – 1 –
5 5 3 2 2 3
2 2 1 – – –
– – 1 – – –
6 7 5 4 – –
Dosimetrist
Base of tongue
Parotid
Brain (continued) Esophagus
reported to occur in 55% of radiation therapy centers around Australia in 20101 and 30% to 60% of cancer patients were being treated with IMRT in the United States in 2008.2 IMRT is the preferred treatment technique for certain clinical sites as it is known to achieve superior target conformity and normal tissue sparing than other treatment techniques.3 IMRT also offers the potential of improving the therapeutic index by allowing increased doses to be safely delivered to the target with acceptable acute and late toxicities.4 The advantages of IMRT compared with conventional 3-dimensional conformal radiation therapy come at the expense of increased treatment complexity. A variety of treatment planning techniques and optimization methods have been employed in IMRT planning, which can lead to variation in the final plan produced and therefore variation in treatment delivery.2,3,5-7 In the context of clinical trials, consistency in treatment planning enabling subsequent uniformity in treatment delivery is necessary. This will, in turn, ensure that equivalent treatment for standard prescriptions is delivered between centers. Variation in treatment planning approaches and experience of centers in IMRT treatment planning has been shown to result in variations in IMRT treatment plans. These variations may be reduced with strict adherence to protocols and guidelines.8-10 Benchmarking and assessment of the ability of an institution to safely plan and deliver IMRT has been utilized for a number of clinical trials.11-13 These multicenter studies only considered differences between centers by assessing 1 plan per center. These studies did not control for dosimetrist experience, and have not assessed intradepartmental IMRT planning variability. IMRT planning is a complex process where dosimetrists are expected to have an understanding of how to adjust plan parameters to achieve planning aims. Different dosimetrists may use different planning techniques that may or may not produce the same end result. Because of the increased degrees of freedom associated with IMRT planning, experience and complexities should be considered. This was a feasibility study to assess the quality of an IMRT plan generated by radiation therapy dosimetrists and to determine if plan quality may show variation with dosimetrist experience.
Spinal lesion
Anus
Prostate
Total
Methods and materials Treatment planning Six dosimetrists in 1 radiation therapy department, each with different levels of IMRT planning experience, were invited to participate in this study. All dosimetrists received the same formal training in IMRT planning according to the departmental standard training requirements. The training was completed in 2 stages. Stage 1 involved planning 5 nonclinical cases for 3 different tumor sites (3 X head and neck, 1 X prostate, 1 X anal canal), and stage 2 involved planning 5 clinical cases for any tumor sites. At the end of each stage the dosimetrists were assessed and deemed competent by the trainer before they could proceed to IMRT planning without supervision. Levels of IMRT planning experience for this study were measured by the number of IMRT plans completed prior to this study and are outlined in Table 1. The computed tomographic data of a 55-year-old man previously treated with IMRT for a stage IVB (T2N3M0) left tonsillar carcinoma complete with contours of the gross tumor volume, planning target volumes (PTV), and all organs at risk used for planning was supplied to each dosimetrist. Dosimetrists were requested to generate an IMRT plan in accordance with the department's planning protocol as displayed in Table 2. Dose to the 70 Gy and 54 Gy PTVs were to be delivered simultaneously in a single phase. The supplied planning guideline specified that the critical structure constraints for spinal cord, brainstem, and mandible were the most important planning priorities, followed by meeting the PTV prescription goals. Satisfying the other normal tissue objectives such as the contralateral parotid, oral cavity, and larynx was noted as important but that this should not compromise dose coverage of the PTV. All plans were generated using a 3-dimensional radiation therapy planning system (Xio V4.4.0; Elekta, Stockholm, Sweden) using step and shoot delivery on a Siemens ONCOR linear accelerator (Siemens Medical Systems, Concord, CA) with 6-MV photon energy.
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IMRT planning experience
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Table 1 (continued) Dosimetrist
Base of tongue
Parotid
Brain
Esophagus
Spinal lesion
Anus
Prostate
Total
A B C D E F
3 4 3 2 2 1
– – 3 2 – 1
– – – 1 – 1
2 – – – – 1
2 – – – – –
3 – – – – 1
– – 1 – – –
43 36 24 22 13 11
Plan evaluation Visual slice by slice review of the isodose distribution was undertaken by an experienced head and neck radiation oncologist to assess the clinical acceptance of each plan. The radiation oncologist was blinded to which dosimetrist had done each plan. For each structure, quantitative evaluation of the dose-volume histogram was used to assess plans against the supplied planning criteria. Several conformity indices were determined as additional quantitative assessment of each plan (Table 3).14,15
Treatment evaluation Treatment delivery was assessed by comparing the number of beams, segments, and total monitor units.
Table 2
Planning protocol supplied to each dosimetrist
Prescription PTV54
PTV70
95% of PTV54 ≥ 54 Gy 99% of PTV54 ≥ 50.2 Gy b20% of PTV54 N 65.3 Gy b5% of PTV54 N 68.3 Gy 95% of PTV70 ≥ 70 Gy 99% of PTV70 ≥ 65.1 Gy b20% of PTV54 N 77 Gy b5% of PTV70 N 80 Gy Mean dose ≤ 74 Gy
Critical structure constraints Brainstem Spinal cord Mandible
Maximum b 54 Gy Maximum b 45 Gy Maximum b 70 Gy
Other structure objectives: Right parotid Oral cavity Glottic larynx
Mean b26 Gy Mean b40 Gy Mean b45 Gy
PTV, planning target volume.
Treatment delivery time was also measured from the first beam on to the last beam off for each plan for a Siemens ONCOR linear accelerator. The accuracy of dose delivery of each plan was assessed using standard clinical IMRT quality assurance procedures. Dose delivery assessment was included in this study to investigate trends in the accuracy of dose delivery with plan complexity, which in turn may be related to planning technique and dosimetrist experience. The measurements were completed using the same linear accelerator in a single session to ensure consistency in dose output and setup. Dose verification included measuring the planar dose for each field with a 2dimensional ionization chamber array and comparing the measured dose with the planar dose calculated by the treatment planning system. The planar dose was calculated by the planning system for each IMRT field with perpendicular incidence onto a water equivalent cubic phantom using the same source-to-surface distance and depth as used for measurement. The comparison was made using gamma evaluation tools on commercial software (OmniPro IMRT V1.6). Acceptance criteria of each plan are outlined in Table 4.
Results Plan analysis The compliance with the planning protocol is listed in Table 5. Only 3 dosimetrists (A, B, and D) were able to satisfy the prescription criteria for the PTVs. All dosimetrists were able to meet the constraints for brainstem, spinal cord, mandible, and oral cavity except for dosimetrist D who failed to meet the constraint for mandible. Figure 1 shows that even though dosimetrists A and F achieved a similar dose-volume histogram for PTV70, variations exist for brainstem, spinal cord, and mandible. None of the dosimetrists were able to meet the planning objectives for the right parotid and larynx due to overlap of these structures with the PTV; however, this was deemed acceptable given that dosimetrists were
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Table 3 Definition of indices used as quantitative assessment Parameter Conformity index (CI)
Definition PIVa PTV b
Conformity number (CN)
PTV95 PTV
Homogeneity index (HI)
D2−D98 D50
×
Optimal value 1-2 b
PTV95 PIVa c
1 0
a
PIV: prescription isodose-volume; volume of reference isodose (95%). b PTV95: volume of the planning target volume (PTV) receiving at least 95% of the total dose. c D2, D98, and D50: dose received by 2%, 98%, and 50% of the PTV, respectively.
instructed not to compromise dose coverage to the PTV in order to satisfy these objectives. On visual slice by slice inspection of the isodose distribution of the plans, the radiation oncologist deemed that all plans were clinically acceptable with plans A and B as the most preferred plans, and plans E and F the least preferred plans.
Conformity indices All plans were within the range of the optimal values specified for conformity indices. Conformity indices calculated were comparable among the 6 plans with the following mean values: conformity index = 1.35 (1.221.42); conformity number = 0.75 (0.70-0.81); and homogeneity index = 0.10 (0.09-0.12).
efficiency measured by the number of segments, total monitor units, and treatment delivery time is displayed in Fig 2. The treatment delivery time ranged from 15.3 minutes for dosimetrist A to 24.4 minutes for dosimetrist E. The higher treatment delivery time for dosimetrist E can be attributed to the higher number of segments generated in the plan. Dosimetrist A had the lowest total monitor unit and number of segments with comparable results achieved by dosimetrists B, C, and D. As IMRT planning experience increased, treatment delivery efficiency also increased as measured by the considerable reduction in total monitor units, number of segments, and delivery time. Dose delivery assessment of each plan showed that plans A, B, C, and D met the gamma acceptance criteria with minor violation, and plans E and F did not meet the gamma acceptance criteria due to major violation.
Discussion The visual slice by slice review of the dose distribution showed that the 6 plans were similar, with a few minor variations. Further analysis of the dose-volume histograms of individual plans showed that only dosimetrist A and B, the 2 most experienced dosimetrists in this study, were able to meet the strict PTV aims and critical structure constraints. Dosimetrist F had the worst planning outcome as seen by the inability to reach a few PTV aims. This is consistent with Williams et al10 who discussed that lack of
Table 5 Planning protocol supplied and the corresponding compliance by each dosimetrist
Treatment delivery
Variable
All dosimetrists used 7 beam angles, except dosimetrist F who used 9 beam angles. The treatment delivery
Table 4 Acceptance criteria of gamma assessment using 3 mm distance to agreement and 2 cGy dose difference with 10 cGy low-dose threshold Pass
Minor violation
Major violation
Individual fields
% gamma b 1== N95%
% gamma b1== N 90%, b 95%
Exceeds minor violation criteria
Total plan
All fields pass
Not more than 2 fields with violations and not more than 1 of these 2 fields with a major violation
Prescription PTV 54 95% of PTV54 ≥ 54 Gy 99% of PTV54 ≥ 50.2 Gy b20% of PTV54 N 65.3 Gy b5% of PTV54 N 68.3 Gy PTV70 95% of PTV70 ≥ 70 Gy 99% of PTV70 ≥ 65.1 Gy b20% of PTV70 N 77 Gy b5% of PTV70 N 80 Gy Mean dose ≤ 74 Gy Constraints Brainstem b 54 Gy Spinal cord b 45 Gy Mandible b 70 Gy Objectives Right parotid, mean b 26 Gy Oral cavity, mean b40 Gy Larynx, mean b 45 Gy
Dosimetrist A
B
C
D
E
F
√ √ √ √
√ √ √ √
√ √ √ x
√ √ √ √
√ √ √ x
x √ √ x
√ √ √ √ √
√ √ √ √ √
√ √ √ √ √
√ √ √ √ √
√ √ √ √ √
x √ √ √ √
√ √ √
√ √ √
√ √ √
√ √ x
√ √ √
√ √ √
x √ x
x √ x
x √ x
x √ x
x √ x
x √ x
Practical Radiation Oncology: July-September 2013
Figure 1
IMRT planning experience
e103
Dose-volume histograms comparing the plan between dosimetrists A and F. PTV, planning target volume.
IMRT planning experience may have contributed to the failure in satisfying dose constraints. The conformity indices measured in this study showed that all 6 plans were comparable for conformity index, conformity number, and homogeneity index. Dose homogeneity characterizes the uniformity of absorbeddose distribution within the target volume and dose conformity characterizes the degree to which the highdose region conforms to the target volume.15 The dosimetrists in this study were all able to produce a plan that reached the optimal indices recommended14,15 for both dose homogeneity and conformity. However, these indices should not be relied upon as a standalone value without considering other factors. Feuvret et al16 concluded that conformity indices are too diverse to quantify the quality of a treatment with 100% sensitivity and specificity, and attempts to reduce conformation to a single index could lead to omission of essential
information. It is recommended that conformity and homogeneity indices be used to complement classical plan assessment.14 The treatment delivery parameters measured by the number of beams, segments, and total monitor units and the treatment delivery time varied considerably among the 6 plans. All dosimetrists in this study used 7 beam angles in their plans, except for dosimetrist F, who used 9 beam angles. Beam configuration may have significant influence on IMRT dose distribution,17 and the final results may strongly depend on the dosimetrist experience, intuition, and understanding of the planning system.18 When analyzing the number of segments and total monitor units for dosimetrists who used the same number of beam angles (dosimetrists A to E), the number of segments and total monitor units increased as the IMRT planning experience decreased. Dosimetrist E had 73 more segments compared with dosimetrist A. A closer look at
Figure 2 Treatment delivery parameters generated by the 6 dosimetrists outlining total monitor units, number of segments, and treatment delivery time.
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each plan showed that the plan generated by dosimetrist E had a large number of small segments that were less than 2 cm. Sharpe et al19 reported that a simple plan is less sensitive to geometric uncertainties and can be delivered with higher accuracy than a plan with many small and irregular segments. The plan by dosimetrist E also had the highest number of total monitor units and almost 2 times that of dosimetrist A. It is estimated that there will be an increased incidence of radiation-induced secondary malignancy by 0.25% for surviving patients who have previously received IMRT due to an increase in monitor units compared with patients who received conventional 3dimensional conformal radiation therapy, likely to be due to increased leakage and scatter radiation associated with larger monitor units.20 Thus, larger numbers of monitor units increasing scattered dose to surrounding tissues should be avoided wherever possible. A method to provide a tool for controlling the number of segments has been proposed in literature, which in turn provides some control of the monitor units.21 The method has the potential for supporting the dosimetrist in finding a reasonable tradeoff between plan quality and treatment complexity. Individual centers could establish guidelines for maximum number of segments and monitor units based on tumor site, above which the IMRT plan should be critically reviewed by a medical physicist and radiation oncologist. When treatment delivery time was compared, the most experienced dosimetrist produced a plan that was delivered in 62% of the time required for the plan produced by the least experienced dosimetrist. Increased treatment time is likely to result in increased patient movement, potentially compromising treatment effectiveness. It has also been reported that total time to deliver a single fraction may have a significant impact on IMRT treatment outcome due to decrease in cell killing with increasing delivery time.22 Increased treatment delivery time would also have an impact on a center's patient throughput, affecting the capacity to reduce patient waiting time. Any IMRT plan of exceptionally long treatment delivery time should be critically reviewed by a medical physicist or radiation oncologist to ensure if such a treatment delivery time is necessary. Dose delivery accuracy was assessed to compare the dose distribution with the planned dose. Dosimetrists E and F did not meet the acceptance criteria for the gamma measurement, indicating that the dose distribution did not match the planned dose. This could be due to the more complex treatment delivery parameters13 generated by these dosimetrists as indicated by the higher number of segments and total monitor units. Although the dosimetrists would have no control during the planning stages in ensuring that the planned dose would meet the gamma measurements criteria, this study showed that less complex plans (A, B, C, and D) were able to meet the criteria indicating that IMRT planning experience may play an indirect role in this.
Practical Radiation Oncology: July-September 2013
In this study assessing a single head and neck treatment plan, dosimetrists with more IMRT planning experience produced a higher quality plan and were able to better adhere to the planning goals supplied. The outcome of this planning study reflects the importance of dosimetrist experience in IMRT planning. Obtaining good plans for complex cases is often difficult and requires hands-on experience and extensive training.6 Dosimetrists should be made aware of the importance of the appropriate beam configurations, the significance of making a sound clinical judgment in setting the planning objectives on the treatment planning system, and the consequence of the final number of segments and monitor units and how this may impact on the treatment delivery time. It is important that these factors be included and assessed in the benchmarking process during training. As IMRT is continuously evolving and dynamic, continuing education could be important for maintaining skills.6 Along with experience and training, another contributing factor to plan quality could be the level of teamwork among dosimetrists, physicists, and radiation oncologists. In this study we removed some of the day-to-day practical factors, such as variations in clinical priorities determined by the radiation oncologist, which might affect plan outcomes. In clinical practice the more experienced dosimetrists approach the plan more holistically and typically have developed a better understanding of the many clinical and technical considerations with medical physicists and radiation oncologists. This knowledge and experience could only be obtained from the various discussions with the medical physicists and radiation oncologists for individual patients in the past. In contrast, the less experienced dosimetrists in this study were only focused on meeting the planning guidelines dosimetrically. IMRT treatment planning requires a multidisciplinary team approach and relies heavily on good teamwork and effective communication among dosimetrists, radiation oncologists, and medical physicists. In a multidisciplinary strategy, progress in radiation therapy is based on a global approach of the patient and personalized, well-targeted treatment of the tumor.23 Dosimetrists should be encouraged to adopt this team approach and work closely with radiation oncologists and medical physicists on each IMRT plan. Use of a class solution, which offers the potential for streamlining the planning process and reducing the learning curve has been proposed for various tumor sites.24-26 If this approach had been used in this study it may have contributed in reducing the difference seen in treatment delivery parameters among the dosimetrists. Class solutions may provide a guideline as a starting point for a plan but may not be the finishing point. In our clinical experience with head and neck IMRT, knowledge of IMRT fundamentals and planning experience is still necessary to be able to adjust plan parameters for individual patients and achieve the final planning aims.
Practical Radiation Oncology: July-September 2013
There are some apparent differences in IMRT plans that have been shown in multicenter planning comparison studies. Some of these are target volume and critical structure variability,27 the ability of different treatment planning systems to achieve the desired planning objectives,28 and different optimization parameters. However, this study has shown that variables in IMRT planning can exist within a center despite using the same treatment planning system and receiving the same training program prior to clinical planning. It is possible that for a low complexity case like prostate in general, dosimetrist experience may not have a significant impact on the plan quality, as concluded by Nelms et al29 in a recent interinstitutional study. Limitations of this feasibility study include that it was a single patient study and the range of dosimetrist experience was relatively small. Time taken to generate the plans was also not acquired. Despite these limitations our results suggest a relationship may exist between dosimetrist experience and treatment quality for IMRT. Further investigation is required to see if this trend continues with a larger patient cohort and wider range of dosimetrist experience.
IMRT planning experience
3.
4.
5.
6.
7.
8.
9.
Conclusions Dosimetrists with higher levels of IMRT planning experience produced a superior IMRT plan for the head and neck case considered. Plans produced by inexperienced dosimetrists, while dosimetrically inferior, were clinically acceptable but tended to be more complex, resulting in increased treatment time and reduced dose delivery accuracy. Further studies are required to determine if these findings persist for different plans and different treatment sites.
10.
11.
12.
13.
14.
Acknowledgments The authors wish to thank Skye Blakeney BAppSc, Isabella Franji BAppSc, Kathy Andrew MHlthSci, Carol Nguyen BAppSc, and Andrew Wallis MSc for completing the plans presented in this study. We are also very grateful to Shivani Kumar MPH for her constructive comments during the development of this study.
References 1. Brown RL, Butler DJ. The 2009 survey of therapy equipment and dosimetry practices in Australian radiotherapy centres. Australas Phys Eng Sci Med. 2010;33:285-297. 2. Das IJ, Cheng CW, Chopra KL, Mitra RK, Srivastava SP, Glatstein E. Intensity-modulated radiation therapy dose prescrip-
15.
16. 17.
18.
19.
20. 21.
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tion, recording, and delivery: patterns of variability among institutions and treatment planning systems. J Nat Cancer Inst. 2008;100:300-307. Intensity Modulated Radiation Collaborative Working Group. Intensity-modulated radiotherapy: current status and issues of interest. Int J Radiat Oncol Biol Phys. 2001;51:880-914. Ghilezan M, Yan D, Liang J, Jaffray D, Wong J, Martinez A. Online image-guided intensity-modulated radiotherapy for prostate cancer: how much improvement can we expect? A theoretical assessment of clinical benefits and potential dose escalation by improving precision and accuracy of radiation delivery. Int J Radiat Oncol Biol Phys. 2004;60:1602-1610. Hartford AC, Palisca MG, Eichler TJ, et al. American Society for Therapeutic Radiology and Oncology (ASTRO) and American College of Radiology (ACR) Practice Guidelines for IntensityModulated Radiation Therapy (IMRT). Int J Radiat Oncol Biol Phys. 2009;73:9-14. Galvin JM, Ezzell G, Eisbrauch A, et al. Implementing IMRT in clinical practice: a joint document of the American Society for Therapeutic Radiology and Oncology and the American Association of Physicists in Medicine. Int J Radiat Oncol Biol Phys. 2004;58:1616-1634. Ezzell GA, Galvin JM, Low D, et al. Guidance document on delivery, treatment planning, and clinical implementation of IMRT: report of the IMRT Subcommittee of the AAPM Radiation Therapy Committee. Med Phys. 2003;30:2089-2115. Thomas SJ, Vinall A, Poynter A, Routsis D. A multicentre timing study intensity-modulated radiotherapy planning and delivery. Clin Oncol (R Coll Radiol). 2010;22:658-665. Bohsung J, Gillis S, Arrans R, et al. IMRT treatment planning: a comparative inter-system and inter-centre planning exercise of the QUASIMODO group. Radiother Oncol. 2005;76:354-361. Williams MJ, Bailey M, Forstner D, Metcalfe PE. Multicentre quality assurance of intensity-modulated radiation therapy plans: a precursor to clinical trials. Australas Radiol. 2007;51:472-479. Healy B, Frantzis J, Murry R, et al. Development of a dosimetry inter-comparison for IMRT as part of site credentialing for a TROG multi-centre clinical trial for prostate cancer. Australas Phys Eng Sci Med. 2011;34:195-202. Clark CH. Nordmark Hansen V, Chantler H, et al. Dosimetry audit for a multi-centre IMRT head and neck trial. Radiother Oncol. 2009; 93:102-108. Ezzell GA, Burmeister JW, Dogan N, et al. IMRT commissioning: multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119. Med Phys. 2009;36:5359-5373. Musat E, Roelofs E, Bar-Deroma R, et al. Dummy run and conformity indices in the ongoing EORTC low-grade glioma trial 22033-26033: first evaluation of quality of radiotherapy planning. Radiother Oncol. 2010;95:218-224. ICRU Report 83: prescribing, recording, and reporting photon-beam intensity-modulated radiation therapy (IMRT). Journal of the ICRU. 2010. Feuvret L, Noël G, Mazeron JJ, Bey P. Conformity index: a review. Int J Radiat Oncol Biol Phys. 2006;64:333-342. Pugachev A, Li JG, Boyer AL, et al. Role of beam orientation optimization in intensity-modulated radiation therapy. Int J Radiat Oncol Biol Phys. 2001;50:551-560. Pugachev A, Xing L. Incorporating prior knowledge into beam orientation optimization in IMRT. Int J Radiat Oncol Biol Phys. 2002;54:1565-1574. Sharpe MB, Miller BM, Yan D, Wong JW. Monitor unit settings for intensity modulated beams delivered using a step-and-shoot approach. Med Phys. 2000;27:2719-2725. Hall EJ, Wuu CS. Radiation-induced second cancers: the impact of 3D-CRT and IMRT. Int J Radiat Oncol Biol Phys. 2003;56:83-88. Carlsson F. Combining segment generation with direct step-and shoot optimization in intensity-modulated radiation therapy. Med Phys. 2008;35:3828-3838.
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22. Wang JZ, Li XA, D'Souza WD, Stewart RD. Impact of prolonged fraction delivery times on tumor control: a note of caution for intensity-modulated radiation therapy. Int J Radiat Oncol Biol Phys. 2003;57:543-552. 23. Gérard JP, Thariat J, Giraud P, Cosset JM. Past, present and near future of techniques in radiation oncology (Article in French). Bull Cancer. 2010;97:743-751. 24. Lievens Y, Nulens A, Gaber MA, et al. Intensity-modulated radiotherapy for locally advanced non-small-cell lung cancer: a dose-escalation planning study. Int J Radiat Oncol Biol Phys. 2011; 80:306-313. 25. Rodrigues G, Yartsev S, Chen J, et al. A comparison of prostate IMRT and helical tomotherapy class solutions. Radiother Oncol. 2006;80:374-377.
Practical Radiation Oncology: July-September 2013 26. Xia P, Lee N, Liu Y-M, et al. A study of planning dose constraints for treatment of nasopharyngeal carcinoma using a commercial inverse treatment planning system. Int J Radiat Oncol Biol Phys. 2004;59:886-896. 27. Matzinger O, Poortmans P, Giraud JY, et al. Quality assurance in the 22991 EORTC ROG trial in localized prostate cancer: dummy run and individual case review. Radiother Oncol. 2009; 90:285-290. 28. Senthi S, Gill SS, Haworth A, et al. Benchmarking dosimetric quality assessment of prostate intensity-modulated radiotherapy. Int J Radiat Oncol Biol Phys. 2012;82:998-1005. 29. Nelms BE, Robinson G, Markham J, et al. Variation in external beam treatment plan quality: an inter-institutional study of planners and planning systems. Pract Radiat Oncol. 2012;2(4):296-305.
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Original Report
How important is dosimetrist experience for intensity modulated radiation therapy? A comparative analysis of a head and neck case Vikneswary Batumalai MHlthSc a,b,⁎, Michael G. Jameson BMedRadPhys a,c , Dion F. Forstner MD a,d , Philip Vial PhD a,e , Lois C. Holloway PhD a,b,c,e a
Cancer Therapy Centre, Liverpool Hospital, Sydney, Australia University of New South Wales, NSW, Australia c Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia d Collaboration of Cancer Outcome Research and Evaluation (CCORE), Liverpool Hospital, Sydney, Australia e Institute of Medical Physics, School of Medical Physics, University of Sydney, Sydney, Australia b
Received 27 March 2012; revised 4 June 2012; accepted 22 June 2012
Abstract Purpose: Treatment planning for IMRT is a complex process that requires additional training and expertise. The aim of this study was to compare and analyze IMRT plans generated by dosimetrists with varying levels of IMRT planning experience. Methods and Materials: The computed tomography (CT) data of a patient previously treated with IMRT for left tonsillar carcinoma were used. The patient's preexisting planning target volumes (PTVs) and all organs at risk were provided with the CT data set. Six dosimetrists with variable IMRT planning experience generated IMRT plans according to the department's protocol. Plan analysis included visual inspection and comparison of dose-volume histogram, conformity indices, treatment delivery efficiency, and dose delivery accuracy. Results: Visual review of the dose distribution showed that the 6 plans were comparable. However, only the 2 most experienced dosimetrists were able to meet the strict PTV aims and critical structure constraints. The least experienced dosimetrist had the worst planning outcome. Comparison of delivery efficiency showed that the number of segments, total monitor units, and treatment time increased as the IMRT planning experience decreased. Conclusions: Dosimetrists with higher levels of IMRT planning experience produced a better quality head and neck IMRT plan. Different planning experience may need to be considered when organizing appropriate departmental resources. Crown Copyright © 2013 Published by Elsevier Inc. on behalf of American Society for Radiation Oncology. All rights reserved.
Presented at the 11th Biennial Meeting of European Society for Therapeutic Radiology and Oncology (ESTRO), London, UK, May 8-12, 2011. Conflicts of interest: None. ⁎ Corresponding author. Cancer Therapy Centre, Liverpool Hospital, Locked Bag 7103, Liverpool BC, NSW 1871, Australia. E-mail address: [email protected] (V. Batumalai).
Introduction Intensity modulated radiation therapy (IMRT) has become the standard of care for many patients in radiation therapy for a variety of tumor sites. IMRT planning was
1879-8500/$ – see front matter. Crown Copyright © 2013 Published by Elsevier Inc. on behalf of American Society for Radiation Oncology. All rights reserved. http://dx.doi.org/10.1016/j.prro.2012.06.009
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V. Batumalai et al
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Dosimetrist intensity modulated radiation therapy planning experience based on tumor site
Dosimetrist
Nasopharynx
Tonsil
Nasal cavity
Pharynx
Palate
Glottis
Pyriform sinus
Maxilla
Larynx
A B C D E F
5 3 3 3 2 2
5 4 2 3 3 –
4 2 – – – –
4 6 1 4 3 1
2 3 – – 1 –
5 5 3 2 2 3
2 2 1 – – –
– – 1 – – –
6 7 5 4 – –
Dosimetrist
Base of tongue
Parotid
Brain (continued) Esophagus
reported to occur in 55% of radiation therapy centers around Australia in 20101 and 30% to 60% of cancer patients were being treated with IMRT in the United States in 2008.2 IMRT is the preferred treatment technique for certain clinical sites as it is known to achieve superior target conformity and normal tissue sparing than other treatment techniques.3 IMRT also offers the potential of improving the therapeutic index by allowing increased doses to be safely delivered to the target with acceptable acute and late toxicities.4 The advantages of IMRT compared with conventional 3-dimensional conformal radiation therapy come at the expense of increased treatment complexity. A variety of treatment planning techniques and optimization methods have been employed in IMRT planning, which can lead to variation in the final plan produced and therefore variation in treatment delivery.2,3,5-7 In the context of clinical trials, consistency in treatment planning enabling subsequent uniformity in treatment delivery is necessary. This will, in turn, ensure that equivalent treatment for standard prescriptions is delivered between centers. Variation in treatment planning approaches and experience of centers in IMRT treatment planning has been shown to result in variations in IMRT treatment plans. These variations may be reduced with strict adherence to protocols and guidelines.8-10 Benchmarking and assessment of the ability of an institution to safely plan and deliver IMRT has been utilized for a number of clinical trials.11-13 These multicenter studies only considered differences between centers by assessing 1 plan per center. These studies did not control for dosimetrist experience, and have not assessed intradepartmental IMRT planning variability. IMRT planning is a complex process where dosimetrists are expected to have an understanding of how to adjust plan parameters to achieve planning aims. Different dosimetrists may use different planning techniques that may or may not produce the same end result. Because of the increased degrees of freedom associated with IMRT planning, experience and complexities should be considered. This was a feasibility study to assess the quality of an IMRT plan generated by radiation therapy dosimetrists and to determine if plan quality may show variation with dosimetrist experience.
Spinal lesion
Anus
Prostate
Total
Methods and materials Treatment planning Six dosimetrists in 1 radiation therapy department, each with different levels of IMRT planning experience, were invited to participate in this study. All dosimetrists received the same formal training in IMRT planning according to the departmental standard training requirements. The training was completed in 2 stages. Stage 1 involved planning 5 nonclinical cases for 3 different tumor sites (3 X head and neck, 1 X prostate, 1 X anal canal), and stage 2 involved planning 5 clinical cases for any tumor sites. At the end of each stage the dosimetrists were assessed and deemed competent by the trainer before they could proceed to IMRT planning without supervision. Levels of IMRT planning experience for this study were measured by the number of IMRT plans completed prior to this study and are outlined in Table 1. The computed tomographic data of a 55-year-old man previously treated with IMRT for a stage IVB (T2N3M0) left tonsillar carcinoma complete with contours of the gross tumor volume, planning target volumes (PTV), and all organs at risk used for planning was supplied to each dosimetrist. Dosimetrists were requested to generate an IMRT plan in accordance with the department's planning protocol as displayed in Table 2. Dose to the 70 Gy and 54 Gy PTVs were to be delivered simultaneously in a single phase. The supplied planning guideline specified that the critical structure constraints for spinal cord, brainstem, and mandible were the most important planning priorities, followed by meeting the PTV prescription goals. Satisfying the other normal tissue objectives such as the contralateral parotid, oral cavity, and larynx was noted as important but that this should not compromise dose coverage of the PTV. All plans were generated using a 3-dimensional radiation therapy planning system (Xio V4.4.0; Elekta, Stockholm, Sweden) using step and shoot delivery on a Siemens ONCOR linear accelerator (Siemens Medical Systems, Concord, CA) with 6-MV photon energy.
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Table 1 (continued) Dosimetrist
Base of tongue
Parotid
Brain
Esophagus
Spinal lesion
Anus
Prostate
Total
A B C D E F
3 4 3 2 2 1
– – 3 2 – 1
– – – 1 – 1
2 – – – – 1
2 – – – – –
3 – – – – 1
– – 1 – – –
43 36 24 22 13 11
Plan evaluation Visual slice by slice review of the isodose distribution was undertaken by an experienced head and neck radiation oncologist to assess the clinical acceptance of each plan. The radiation oncologist was blinded to which dosimetrist had done each plan. For each structure, quantitative evaluation of the dose-volume histogram was used to assess plans against the supplied planning criteria. Several conformity indices were determined as additional quantitative assessment of each plan (Table 3).14,15
Treatment evaluation Treatment delivery was assessed by comparing the number of beams, segments, and total monitor units.
Table 2
Planning protocol supplied to each dosimetrist
Prescription PTV54
PTV70
95% of PTV54 ≥ 54 Gy 99% of PTV54 ≥ 50.2 Gy b20% of PTV54 N 65.3 Gy b5% of PTV54 N 68.3 Gy 95% of PTV70 ≥ 70 Gy 99% of PTV70 ≥ 65.1 Gy b20% of PTV54 N 77 Gy b5% of PTV70 N 80 Gy Mean dose ≤ 74 Gy
Critical structure constraints Brainstem Spinal cord Mandible
Maximum b 54 Gy Maximum b 45 Gy Maximum b 70 Gy
Other structure objectives: Right parotid Oral cavity Glottic larynx
Mean b26 Gy Mean b40 Gy Mean b45 Gy
PTV, planning target volume.
Treatment delivery time was also measured from the first beam on to the last beam off for each plan for a Siemens ONCOR linear accelerator. The accuracy of dose delivery of each plan was assessed using standard clinical IMRT quality assurance procedures. Dose delivery assessment was included in this study to investigate trends in the accuracy of dose delivery with plan complexity, which in turn may be related to planning technique and dosimetrist experience. The measurements were completed using the same linear accelerator in a single session to ensure consistency in dose output and setup. Dose verification included measuring the planar dose for each field with a 2dimensional ionization chamber array and comparing the measured dose with the planar dose calculated by the treatment planning system. The planar dose was calculated by the planning system for each IMRT field with perpendicular incidence onto a water equivalent cubic phantom using the same source-to-surface distance and depth as used for measurement. The comparison was made using gamma evaluation tools on commercial software (OmniPro IMRT V1.6). Acceptance criteria of each plan are outlined in Table 4.
Results Plan analysis The compliance with the planning protocol is listed in Table 5. Only 3 dosimetrists (A, B, and D) were able to satisfy the prescription criteria for the PTVs. All dosimetrists were able to meet the constraints for brainstem, spinal cord, mandible, and oral cavity except for dosimetrist D who failed to meet the constraint for mandible. Figure 1 shows that even though dosimetrists A and F achieved a similar dose-volume histogram for PTV70, variations exist for brainstem, spinal cord, and mandible. None of the dosimetrists were able to meet the planning objectives for the right parotid and larynx due to overlap of these structures with the PTV; however, this was deemed acceptable given that dosimetrists were
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Table 3 Definition of indices used as quantitative assessment Parameter Conformity index (CI)
Definition PIVa PTV b
Conformity number (CN)
PTV95 PTV
Homogeneity index (HI)
D2−D98 D50
×
Optimal value 1-2 b
PTV95 PIVa c
1 0
a
PIV: prescription isodose-volume; volume of reference isodose (95%). b PTV95: volume of the planning target volume (PTV) receiving at least 95% of the total dose. c D2, D98, and D50: dose received by 2%, 98%, and 50% of the PTV, respectively.
instructed not to compromise dose coverage to the PTV in order to satisfy these objectives. On visual slice by slice inspection of the isodose distribution of the plans, the radiation oncologist deemed that all plans were clinically acceptable with plans A and B as the most preferred plans, and plans E and F the least preferred plans.
Conformity indices All plans were within the range of the optimal values specified for conformity indices. Conformity indices calculated were comparable among the 6 plans with the following mean values: conformity index = 1.35 (1.221.42); conformity number = 0.75 (0.70-0.81); and homogeneity index = 0.10 (0.09-0.12).
efficiency measured by the number of segments, total monitor units, and treatment delivery time is displayed in Fig 2. The treatment delivery time ranged from 15.3 minutes for dosimetrist A to 24.4 minutes for dosimetrist E. The higher treatment delivery time for dosimetrist E can be attributed to the higher number of segments generated in the plan. Dosimetrist A had the lowest total monitor unit and number of segments with comparable results achieved by dosimetrists B, C, and D. As IMRT planning experience increased, treatment delivery efficiency also increased as measured by the considerable reduction in total monitor units, number of segments, and delivery time. Dose delivery assessment of each plan showed that plans A, B, C, and D met the gamma acceptance criteria with minor violation, and plans E and F did not meet the gamma acceptance criteria due to major violation.
Discussion The visual slice by slice review of the dose distribution showed that the 6 plans were similar, with a few minor variations. Further analysis of the dose-volume histograms of individual plans showed that only dosimetrist A and B, the 2 most experienced dosimetrists in this study, were able to meet the strict PTV aims and critical structure constraints. Dosimetrist F had the worst planning outcome as seen by the inability to reach a few PTV aims. This is consistent with Williams et al10 who discussed that lack of
Table 5 Planning protocol supplied and the corresponding compliance by each dosimetrist
Treatment delivery
Variable
All dosimetrists used 7 beam angles, except dosimetrist F who used 9 beam angles. The treatment delivery
Table 4 Acceptance criteria of gamma assessment using 3 mm distance to agreement and 2 cGy dose difference with 10 cGy low-dose threshold Pass
Minor violation
Major violation
Individual fields
% gamma b 1== N95%
% gamma b1== N 90%, b 95%
Exceeds minor violation criteria
Total plan
All fields pass
Not more than 2 fields with violations and not more than 1 of these 2 fields with a major violation
Prescription PTV 54 95% of PTV54 ≥ 54 Gy 99% of PTV54 ≥ 50.2 Gy b20% of PTV54 N 65.3 Gy b5% of PTV54 N 68.3 Gy PTV70 95% of PTV70 ≥ 70 Gy 99% of PTV70 ≥ 65.1 Gy b20% of PTV70 N 77 Gy b5% of PTV70 N 80 Gy Mean dose ≤ 74 Gy Constraints Brainstem b 54 Gy Spinal cord b 45 Gy Mandible b 70 Gy Objectives Right parotid, mean b 26 Gy Oral cavity, mean b40 Gy Larynx, mean b 45 Gy
Dosimetrist A
B
C
D
E
F
√ √ √ √
√ √ √ √
√ √ √ x
√ √ √ √
√ √ √ x
x √ √ x
√ √ √ √ √
√ √ √ √ √
√ √ √ √ √
√ √ √ √ √
√ √ √ √ √
x √ √ √ √
√ √ √
√ √ √
√ √ √
√ √ x
√ √ √
√ √ √
x √ x
x √ x
x √ x
x √ x
x √ x
x √ x
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Figure 1
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Dose-volume histograms comparing the plan between dosimetrists A and F. PTV, planning target volume.
IMRT planning experience may have contributed to the failure in satisfying dose constraints. The conformity indices measured in this study showed that all 6 plans were comparable for conformity index, conformity number, and homogeneity index. Dose homogeneity characterizes the uniformity of absorbeddose distribution within the target volume and dose conformity characterizes the degree to which the highdose region conforms to the target volume.15 The dosimetrists in this study were all able to produce a plan that reached the optimal indices recommended14,15 for both dose homogeneity and conformity. However, these indices should not be relied upon as a standalone value without considering other factors. Feuvret et al16 concluded that conformity indices are too diverse to quantify the quality of a treatment with 100% sensitivity and specificity, and attempts to reduce conformation to a single index could lead to omission of essential
information. It is recommended that conformity and homogeneity indices be used to complement classical plan assessment.14 The treatment delivery parameters measured by the number of beams, segments, and total monitor units and the treatment delivery time varied considerably among the 6 plans. All dosimetrists in this study used 7 beam angles in their plans, except for dosimetrist F, who used 9 beam angles. Beam configuration may have significant influence on IMRT dose distribution,17 and the final results may strongly depend on the dosimetrist experience, intuition, and understanding of the planning system.18 When analyzing the number of segments and total monitor units for dosimetrists who used the same number of beam angles (dosimetrists A to E), the number of segments and total monitor units increased as the IMRT planning experience decreased. Dosimetrist E had 73 more segments compared with dosimetrist A. A closer look at
Figure 2 Treatment delivery parameters generated by the 6 dosimetrists outlining total monitor units, number of segments, and treatment delivery time.
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each plan showed that the plan generated by dosimetrist E had a large number of small segments that were less than 2 cm. Sharpe et al19 reported that a simple plan is less sensitive to geometric uncertainties and can be delivered with higher accuracy than a plan with many small and irregular segments. The plan by dosimetrist E also had the highest number of total monitor units and almost 2 times that of dosimetrist A. It is estimated that there will be an increased incidence of radiation-induced secondary malignancy by 0.25% for surviving patients who have previously received IMRT due to an increase in monitor units compared with patients who received conventional 3dimensional conformal radiation therapy, likely to be due to increased leakage and scatter radiation associated with larger monitor units.20 Thus, larger numbers of monitor units increasing scattered dose to surrounding tissues should be avoided wherever possible. A method to provide a tool for controlling the number of segments has been proposed in literature, which in turn provides some control of the monitor units.21 The method has the potential for supporting the dosimetrist in finding a reasonable tradeoff between plan quality and treatment complexity. Individual centers could establish guidelines for maximum number of segments and monitor units based on tumor site, above which the IMRT plan should be critically reviewed by a medical physicist and radiation oncologist. When treatment delivery time was compared, the most experienced dosimetrist produced a plan that was delivered in 62% of the time required for the plan produced by the least experienced dosimetrist. Increased treatment time is likely to result in increased patient movement, potentially compromising treatment effectiveness. It has also been reported that total time to deliver a single fraction may have a significant impact on IMRT treatment outcome due to decrease in cell killing with increasing delivery time.22 Increased treatment delivery time would also have an impact on a center's patient throughput, affecting the capacity to reduce patient waiting time. Any IMRT plan of exceptionally long treatment delivery time should be critically reviewed by a medical physicist or radiation oncologist to ensure if such a treatment delivery time is necessary. Dose delivery accuracy was assessed to compare the dose distribution with the planned dose. Dosimetrists E and F did not meet the acceptance criteria for the gamma measurement, indicating that the dose distribution did not match the planned dose. This could be due to the more complex treatment delivery parameters13 generated by these dosimetrists as indicated by the higher number of segments and total monitor units. Although the dosimetrists would have no control during the planning stages in ensuring that the planned dose would meet the gamma measurements criteria, this study showed that less complex plans (A, B, C, and D) were able to meet the criteria indicating that IMRT planning experience may play an indirect role in this.
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In this study assessing a single head and neck treatment plan, dosimetrists with more IMRT planning experience produced a higher quality plan and were able to better adhere to the planning goals supplied. The outcome of this planning study reflects the importance of dosimetrist experience in IMRT planning. Obtaining good plans for complex cases is often difficult and requires hands-on experience and extensive training.6 Dosimetrists should be made aware of the importance of the appropriate beam configurations, the significance of making a sound clinical judgment in setting the planning objectives on the treatment planning system, and the consequence of the final number of segments and monitor units and how this may impact on the treatment delivery time. It is important that these factors be included and assessed in the benchmarking process during training. As IMRT is continuously evolving and dynamic, continuing education could be important for maintaining skills.6 Along with experience and training, another contributing factor to plan quality could be the level of teamwork among dosimetrists, physicists, and radiation oncologists. In this study we removed some of the day-to-day practical factors, such as variations in clinical priorities determined by the radiation oncologist, which might affect plan outcomes. In clinical practice the more experienced dosimetrists approach the plan more holistically and typically have developed a better understanding of the many clinical and technical considerations with medical physicists and radiation oncologists. This knowledge and experience could only be obtained from the various discussions with the medical physicists and radiation oncologists for individual patients in the past. In contrast, the less experienced dosimetrists in this study were only focused on meeting the planning guidelines dosimetrically. IMRT treatment planning requires a multidisciplinary team approach and relies heavily on good teamwork and effective communication among dosimetrists, radiation oncologists, and medical physicists. In a multidisciplinary strategy, progress in radiation therapy is based on a global approach of the patient and personalized, well-targeted treatment of the tumor.23 Dosimetrists should be encouraged to adopt this team approach and work closely with radiation oncologists and medical physicists on each IMRT plan. Use of a class solution, which offers the potential for streamlining the planning process and reducing the learning curve has been proposed for various tumor sites.24-26 If this approach had been used in this study it may have contributed in reducing the difference seen in treatment delivery parameters among the dosimetrists. Class solutions may provide a guideline as a starting point for a plan but may not be the finishing point. In our clinical experience with head and neck IMRT, knowledge of IMRT fundamentals and planning experience is still necessary to be able to adjust plan parameters for individual patients and achieve the final planning aims.
Practical Radiation Oncology: July-September 2013
There are some apparent differences in IMRT plans that have been shown in multicenter planning comparison studies. Some of these are target volume and critical structure variability,27 the ability of different treatment planning systems to achieve the desired planning objectives,28 and different optimization parameters. However, this study has shown that variables in IMRT planning can exist within a center despite using the same treatment planning system and receiving the same training program prior to clinical planning. It is possible that for a low complexity case like prostate in general, dosimetrist experience may not have a significant impact on the plan quality, as concluded by Nelms et al29 in a recent interinstitutional study. Limitations of this feasibility study include that it was a single patient study and the range of dosimetrist experience was relatively small. Time taken to generate the plans was also not acquired. Despite these limitations our results suggest a relationship may exist between dosimetrist experience and treatment quality for IMRT. Further investigation is required to see if this trend continues with a larger patient cohort and wider range of dosimetrist experience.
IMRT planning experience
3.
4.
5.
6.
7.
8.
9.
Conclusions Dosimetrists with higher levels of IMRT planning experience produced a superior IMRT plan for the head and neck case considered. Plans produced by inexperienced dosimetrists, while dosimetrically inferior, were clinically acceptable but tended to be more complex, resulting in increased treatment time and reduced dose delivery accuracy. Further studies are required to determine if these findings persist for different plans and different treatment sites.
10.
11.
12.
13.
14.
Acknowledgments The authors wish to thank Skye Blakeney BAppSc, Isabella Franji BAppSc, Kathy Andrew MHlthSci, Carol Nguyen BAppSc, and Andrew Wallis MSc for completing the plans presented in this study. We are also very grateful to Shivani Kumar MPH for her constructive comments during the development of this study.
References 1. Brown RL, Butler DJ. The 2009 survey of therapy equipment and dosimetry practices in Australian radiotherapy centres. Australas Phys Eng Sci Med. 2010;33:285-297. 2. Das IJ, Cheng CW, Chopra KL, Mitra RK, Srivastava SP, Glatstein E. Intensity-modulated radiation therapy dose prescrip-
15.
16. 17.
18.
19.
20. 21.
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tion, recording, and delivery: patterns of variability among institutions and treatment planning systems. J Nat Cancer Inst. 2008;100:300-307. Intensity Modulated Radiation Collaborative Working Group. Intensity-modulated radiotherapy: current status and issues of interest. Int J Radiat Oncol Biol Phys. 2001;51:880-914. Ghilezan M, Yan D, Liang J, Jaffray D, Wong J, Martinez A. Online image-guided intensity-modulated radiotherapy for prostate cancer: how much improvement can we expect? A theoretical assessment of clinical benefits and potential dose escalation by improving precision and accuracy of radiation delivery. Int J Radiat Oncol Biol Phys. 2004;60:1602-1610. Hartford AC, Palisca MG, Eichler TJ, et al. American Society for Therapeutic Radiology and Oncology (ASTRO) and American College of Radiology (ACR) Practice Guidelines for IntensityModulated Radiation Therapy (IMRT). Int J Radiat Oncol Biol Phys. 2009;73:9-14. Galvin JM, Ezzell G, Eisbrauch A, et al. Implementing IMRT in clinical practice: a joint document of the American Society for Therapeutic Radiology and Oncology and the American Association of Physicists in Medicine. Int J Radiat Oncol Biol Phys. 2004;58:1616-1634. Ezzell GA, Galvin JM, Low D, et al. Guidance document on delivery, treatment planning, and clinical implementation of IMRT: report of the IMRT Subcommittee of the AAPM Radiation Therapy Committee. Med Phys. 2003;30:2089-2115. Thomas SJ, Vinall A, Poynter A, Routsis D. A multicentre timing study intensity-modulated radiotherapy planning and delivery. Clin Oncol (R Coll Radiol). 2010;22:658-665. Bohsung J, Gillis S, Arrans R, et al. IMRT treatment planning: a comparative inter-system and inter-centre planning exercise of the QUASIMODO group. Radiother Oncol. 2005;76:354-361. Williams MJ, Bailey M, Forstner D, Metcalfe PE. Multicentre quality assurance of intensity-modulated radiation therapy plans: a precursor to clinical trials. Australas Radiol. 2007;51:472-479. Healy B, Frantzis J, Murry R, et al. Development of a dosimetry inter-comparison for IMRT as part of site credentialing for a TROG multi-centre clinical trial for prostate cancer. Australas Phys Eng Sci Med. 2011;34:195-202. Clark CH. Nordmark Hansen V, Chantler H, et al. Dosimetry audit for a multi-centre IMRT head and neck trial. Radiother Oncol. 2009; 93:102-108. Ezzell GA, Burmeister JW, Dogan N, et al. IMRT commissioning: multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119. Med Phys. 2009;36:5359-5373. Musat E, Roelofs E, Bar-Deroma R, et al. Dummy run and conformity indices in the ongoing EORTC low-grade glioma trial 22033-26033: first evaluation of quality of radiotherapy planning. Radiother Oncol. 2010;95:218-224. ICRU Report 83: prescribing, recording, and reporting photon-beam intensity-modulated radiation therapy (IMRT). Journal of the ICRU. 2010. Feuvret L, Noël G, Mazeron JJ, Bey P. Conformity index: a review. Int J Radiat Oncol Biol Phys. 2006;64:333-342. Pugachev A, Li JG, Boyer AL, et al. Role of beam orientation optimization in intensity-modulated radiation therapy. Int J Radiat Oncol Biol Phys. 2001;50:551-560. Pugachev A, Xing L. Incorporating prior knowledge into beam orientation optimization in IMRT. Int J Radiat Oncol Biol Phys. 2002;54:1565-1574. Sharpe MB, Miller BM, Yan D, Wong JW. Monitor unit settings for intensity modulated beams delivered using a step-and-shoot approach. Med Phys. 2000;27:2719-2725. Hall EJ, Wuu CS. Radiation-induced second cancers: the impact of 3D-CRT and IMRT. Int J Radiat Oncol Biol Phys. 2003;56:83-88. Carlsson F. Combining segment generation with direct step-and shoot optimization in intensity-modulated radiation therapy. Med Phys. 2008;35:3828-3838.
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V. Batumalai et al
22. Wang JZ, Li XA, D'Souza WD, Stewart RD. Impact of prolonged fraction delivery times on tumor control: a note of caution for intensity-modulated radiation therapy. Int J Radiat Oncol Biol Phys. 2003;57:543-552. 23. Gérard JP, Thariat J, Giraud P, Cosset JM. Past, present and near future of techniques in radiation oncology (Article in French). Bull Cancer. 2010;97:743-751. 24. Lievens Y, Nulens A, Gaber MA, et al. Intensity-modulated radiotherapy for locally advanced non-small-cell lung cancer: a dose-escalation planning study. Int J Radiat Oncol Biol Phys. 2011; 80:306-313. 25. Rodrigues G, Yartsev S, Chen J, et al. A comparison of prostate IMRT and helical tomotherapy class solutions. Radiother Oncol. 2006;80:374-377.
Practical Radiation Oncology: July-September 2013 26. Xia P, Lee N, Liu Y-M, et al. A study of planning dose constraints for treatment of nasopharyngeal carcinoma using a commercial inverse treatment planning system. Int J Radiat Oncol Biol Phys. 2004;59:886-896. 27. Matzinger O, Poortmans P, Giraud JY, et al. Quality assurance in the 22991 EORTC ROG trial in localized prostate cancer: dummy run and individual case review. Radiother Oncol. 2009; 90:285-290. 28. Senthi S, Gill SS, Haworth A, et al. Benchmarking dosimetric quality assessment of prostate intensity-modulated radiotherapy. Int J Radiat Oncol Biol Phys. 2012;82:998-1005. 29. Nelms BE, Robinson G, Markham J, et al. Variation in external beam treatment plan quality: an inter-institutional study of planners and planning systems. Pract Radiat Oncol. 2012;2(4):296-305.
