Radiation Protection Dosimetry Advance Access published April 20, 2014 Radiation Protection Dosimetry (2014), pp. 1–5
doi:10.1093/rpd/ncu128
IN VIVO DOSE EVALUATION DURING GYNAECOLOGICAL RADIOTHERAPY USING L-ALANINE/ESR DOSIMETRY Amanda Burg Rech1,*, Gustavo Lazzaro Barbi2, Luiz Henrique Almeida Ventura2, Flavio Silva Guimara˜es2, Harley Francisco Oliveira2,3 and Oswaldo Baffa1 1 Departamento de Fı´sica, FFCLRP, Universidade de Sa˜o Paulo, Ribeira˜o Preto, Sa˜o Paulo, Brasil 2 Servic¸o de Radioterapia, HCFMRP, Universidade de Sa˜o Paulo, Ribeira˜o Preto, Sa˜o Paulo, Brasil 3 Departamento de Clı´nica Me´dica, FMRP, Universidade de Sa˜o Paulo, Ribeira˜o Preto, Sa˜o Paulo, Brasil *Corresponding author: [email protected]
INTRODUCTION Gynaecological malignancies are one of the most common tumours in women, resulting in the death of several thousands of women per year(1), even though the potential for cure is high when diagnosed early(2). One of the treatments for these tumours is a 3-D external beam radiation therapy (EBRT). The efficacy of EBRT requires precise administration of the prescribed dose to the tumour with an accuracy between 25 and 7 %, as established by the International Commission on Radiation Units and Measurements (ICRU) report number 50(3). Clinical dosimetry with the alanine/electron spin resonance (ESR) readout method has been reported in the literature for different objectives(4 – 12), but not for EBRT treatment of gynaecological cancer. The widely known advantages of alanine as a dosemeter material in clinical practice are its tissue-equivalent behaviour, signal stability, independence on dose rate, and nontoxicity(13 – 17). In gynaecological malignancies, such as cervical and endometrium cancer, the vaginal wall is notoriously subject to recurrence(18 – 25), highlighting the importance of dosimetry in the tumour region. Therefore, the aim of this study is the verification of the dose administered by adjuvant 3-D EBRT in the treatment target of patients diagnosed with gynaecological cancer using L-alanine and ESR spectrometry. MATERIALS AND METHODS L-alanine
(Sigma-Aldrich) was used in powder form to avoid binder interference in the signal, and was packed into thin gel capsules with an outer diameter of 0.5 cm
and a length of 1 cm. The dosemeter was confined to the capsule volume, as defined by the treatment planning system. The capsules were stored under light and heat protection, and were kept at the same temperature and humidity conditions as that of the laboratory environment. For the ESR measurement the alanine powder was transferred to a quartz tube with a 4-mm inner diameter just before measurements. The ESR spectra of the dosemeters were recorded in an X-band spectrometer from JEOL, model JES-FA200 (9.5 GHz). The system parameters used in all studies reported herein were the same: 100-kHz frequency, 1.0-mT modulation amplitude, 15-mT scan width, 1-min scan time and 0.3-s time constant. The microwave power was 2.5 mW and the mass was 50 mg, length in the quartz tube ,1 cm, covering the high sensitivity part of the resonator cavity. To improve the signal-tonoise ratio, parameters such as the microwave power and the modulation amplitude were optimised. Since alanine dosimetry is a relative method, a calibration curve is essential to correctly relate the absorbed dose recorded by a specific equipment. Alanine detectors were irradiated with 6-MV X rays from a Siemens ONCOR Plus linear accelerator. This machine is routinely calibrated with the ionisation chamber (TRS 398 Protocol) to ensure the delivery dose in daily treatments. To obtain the calibration curve, four dosemeters at a time were irradiated. The dose was determined from the intensity of the peakto-peak amplitude of the averaged alanine spectrum. The phantom study was performed using a pelvic solid water phantom with an acrylic adapter to insert the vaginal device containing the dosemeters.
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at Anadolu University on May 19, 2014
The dose delivered by in vivo 3-D external beam radiation therapy (EBRT) was verified with L-alanine/electron spin resonance (ESR) dosimetry for patients diagnosed with gynaecological cancer. Measurements were performed with an X-band ESR spectrometer. Dosemeters were positioned inside the vaginal cavity with the assistance of an apparatus specially designed for this study. Previous phantom studies were performed using the same conditions as in the in vivo treatment. Four patients participated in this study during 20-irradiation sessions, giving 220 dosemeters to be analysed. The doses were determined with the treatment planning system, providing dose confirmation. The phantom study resulted in a deviation between 22.5 and 2.1 %, and for the in vivo study a deviation between 29.2 and 14.2 % was observed. In all cases, the use of alanine with ESR was effective for dose assessment, yielding results consistent with the values set forth in the International Commission on Radiation Units and Measurements (ICRU) reports.
A. B. RECH ET AL.
Figure 1 shows the pelvic phantom, the device used to hold the dosemeters and a schematic showing the detector distribution inside the device. To define the treatment region and dose, both for the phantom and the in vivo study, a computed tomography (CT) image was taken with a Philips Big Bore CT scanner, and the treatment planning software (TPS) XiO 4.62 from Elekta was used. The dose
RESULTS AND DISCUSSION Figure 3 shows the dose –response curve obtained for L-alanine detectors irradiated with 20– 240 cGy using a 6-MV X-ray linear accelerator. The errors bars correspond to the differences obtained from the mean value of the four dosemeters irradiated at the same dose. The dose –response curve approximates the relationship between dose and ESR signal intensity, given by the following equation: Figure 1. Pelvic solid water phantom with the acrylic adapter and the inserted device (a), the device which holds the alanine dosemeters separated by small chambers denoted by A, B and C (b). Each chamber contains capsules containing L-alanine powder (c).
D ¼ 4:00 IESR 15:48;
ð1Þ
where IESR is the ESR signal intensity normalised by the sample mass (a.u. mg21) and D the dose in cGy. The correlation coefficient is 0.99743.
Figure 2. Example of a CT image (a) and a portal image (b) showing the location of the bone reference ( pelvic symphisys) (large circles) and the radiopaque markers (small circles). The arrows relate the objects to each other, showing their respective location in each image.
Page 2 of 5
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prescribed was equivalent to a pelvic treatment of 180 cGy fraction21. Measurements were carried out in four patients. The prescribed dose was 4.500 cGy, divided into 25 fractions of 180 cGy, with 5 measurements taken from each patient, resulting in the analysis of 220 dosemeters. The apparatus used to put the dosemeters in the treatment region is shown in Figure 1b. Studies began after the approval of the experimental protocol by the Ethics Committee and informed consent was obtained from all patients participating in the study. Radiopaque markers were placed in the apparatus to verify its position before each of the five study sessions. For verification a portal image was taken before each measured session, using bone references to confirm the internal position and the location of the isocentre, as shown in the example in Figure 2. The dose originated from the portal image was negligible compared with the treatment one, 2 cGy. Also, the initial positioning of the markers observed in the CT image enabled the registration and analysis of the CT image with those taken on the day of treatment.
IN VIVO DOSE EVALUATION USING L-ALANINE/ESR DOSIMETRY
Table 1. Results of the phantom study: comparison between the measured and planned dose. Detector chamber
Deviation of the measured from the planned dose (%)
Figure 4. ESR spectrum obtained for a dosemeter irradiated during the CT scan and during a radiotherapy session. It is evident that no dose is detected by the dosemeter during the CT scan.
Table 2. Results of the in vivo study: comparison between the measured and planned doses. Patient
Simulation session 1
2
3
4
22.0 þ0.6 22.5
22.3 21.1 20.9
1.4 0.6 0.4
0.5 2.1 20.6
Detector chamber
Deviation of the measured from the planned dose (%) Session number 1
A B C
Each value of the chamber is a mean value of the dosemeters presented there.
1 2 3
The results of the phantom study are presented in Table 1, in which the measured dose is compared with the planned dose. For the comparison, the following equation was employed: D% ¼
DM DP DP
100 %;
ð2Þ
where DM is the measured dose, DP the planned dose and D% is the percentage difference of the measured dose relative to the planned dose. In contrast to brachytherapy, the deviations between planned and measured single-fraction doses obtained by in vivo radiotherapy dosimetry show no large dose gradient. It is important to note that for the phantom study no heterogeneity correction was employed, and this could result in errors due to the difference in density between solid water (1.00 g cm23) and polymethyl methacrylate (acrylic) (1.18 g cm23). Also, the
4
A B C A B C A B C A B C
2
3
4
5
23.7 þ5.6 þ1.2 þ4.9 þ3.1 þ2.8 20.8 24.7 23.9 þ2.2 þ3.8 25.3 25.6 þ5.0 þ4.9 þ4.2 þ1.9 20.8 þ5.9 þ5.6 þ0.7 þ1.1 þ3.8 þ1.1 þ1.9 þ4.7 þ2.6 þ1.3 þ4.1 22.3 þ14.2 þ10.8 þ3.1 28.3 þ5.6 þ8.8 þ3.3 26.1 24.4 23.6 20.8 þ1.2 20.2 29.2 22.0 þ7.4 þ8.7 þ1.4 20.3 þ9.9 þ13.2 þ6.7 21.3 þ4.2 þ9.9 þ2.3 þ4.5 21.5 20.4 þ5.9
The spaces with (2) represent cases that the region was not inside the treatment field. Presentation of the results is in the same scheme as for the phantom study in Table 1.
studies were performed in different sessions; therefore, the differences reflect errors from all aspects of the procedure from positioning to dose delivery. Table 1 shows that in most cases the results are in compliance with what was proposed by ICRU, as discussed above. The measured doses agreed well with the doses calculated by the TPS. Following the verification of the dosimetry obtained from the phantom study, an in vivo feasibility study was conducted. The
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Downloaded from http://rpd.oxfordjournals.org/ at Anadolu University on May 19, 2014
Figure 3. Dose–response curve for L-alanine detectors irradiated with 20– 240 cGy (6 MV X rays). A linear fitting was made and the outlier curves were set at +95 % of a confidence interval.
A. B. RECH ET AL.
CONCLUSIONS This work was concerned with the verification of the dose in the target volume of the vaginal dome in a 3-D EBRT treatment, especially because of the incidence of tumour recurrence in this region. The calibration curve for the L-alanine/ESR dosimetric systems was linear with the dose in the interval of 20–240 cGy, and the phantom study showed that most of the measured doses are within allowable tolerances, with deviations of 22.5 to 2.1 %. In the in vivo studies, the agreement between the measured dose and the dose calculated from treatment planning complied with that established by ICRU recommendations. Discrepancies are likely to be associated with the movement of the dosemeter probe during the radiotherapy session. ACKNOWLEDGEMENTS Thanks to the Servic¸o de Radioterapia of Hospital das Clı´nicas of FMRP-USP, and to Carlos Brunello, Lourenc¸o Rocha and Jose´ Azziani for technical assistance. FUNDING This work was partially supported by Fundac¸a˜o de Amparo a` Pesquisa do Estado de Sa˜o Paulo (FAPESP) Project 2010/12780-2, Coordenac¸a˜o de Aperfeic¸oamento de Pessoal de Nı´vel Superior (CAPES) and Conselho Nacional de Desenvolvimento Tecnolo´gico (CNPq).
REFERENCES 1. International Agency for Research on Cancer 2012. World Health Organization (accessed 28 November 2012). Available on http://www-dep.iarc.fr/Cancer Mondial.htm. 2. Orr, J. M., Barnett, J. C. and Leath III, C. A. Incidence of subsequent abnormal cytology in cervical cancer patients five-years of post treatment surveillance without evidence of recurrence. Gynecol. Oncol. 122, 501– 504 (2011). 3. International Commission on Radiation Units and Measurements. Report 50: prescribing, recording, and reporting photon beam therapy, Bethesda, MD (1993). 4. Schaeken, B. and Scalliet, P. One year of experience with alanine dosimetry in radiotherapy. Appl. Radiat. Isot. 47, 1177–1182 (1996). 5. Chen, F., Covas, D. T. and Baffa, O. Dosimetry of blood irradiation using an alanine/ESR dosimeter. Appl. Radiat. Isot. 55, 13–16 (2001). 6. Chu, S. et al. ESR/Alanine dosimetry of high-energy electrons in radiotherapy. Appl. Radiat. Isot. 40, 993– 996 (1989). 7. Kudynski, R., Kudynska, J. and Buckmaster, H. A. The application of EPR dosimetry for radiotherapy and radiation protection. Appl. Radiat. Isot. 44, 903– 906 (1993). 8. Ciesielski, B. et al. In vivo alanine/EPR dosimetry in daily clinical practice: a feasibility study. Inter. J. Radiat. Oncol. Biol. Phys. 56, 889–905 (2003). 9. Anton, M. et al. In vivo dosimetry in the urethra using alanine/ESR during 192Ir HDR brachytherapy of prostate cancer—a phantom study. Phys. Med. Biol. 54, 2915–2931 (2009). 10. Schultka, K. et al. EPR/Alanine dosimetry in LDR brachytherapy – A feasibility study. Radiat. Prot. Dosim. 120, 171–175 (2006). 11. Wagner, D. et al. In vivo alanine/electron spin resonance (ESR) dosimetry in radiotherapy of prostate cancer: a feasibility study. Radiother. Oncol. 88, 140–147 (2008). 12. Wagner, D., Anton, M. and Vorwerk, H. Dose uncertainty in radiotherapy of patients with head and neck cancer measured by in vivo ESR/alanine dosimetry using a mouthpiece. Phys. Med. Biol. 56, 1373– 1383 (2011). 13. Regulla, D. F. and Deffner, U. Dosimetry by ESR spectroscopy of alanine. Int. J. Appl. Radiat. Isot. 33, 1101–1114 (1982). 14. Regulla, D. F. and Deffner, U. A system of transfer dosimetry in radiation processing. Radiat. Phys. Chem. 22, 305– 309 (1983). 15. Ciesielski, B., Wielopolski, L. and Reinstein, L. E. The energy response of agar-alanine phantom dosimeter to gamma radiation. Med. Phys. 15, 380– 383 (1988). 16. Ciesielski, B., Wielopolski, L. and Reinstein, L. E. Energy response of agar-alanine free radical dosimetry to therapeutic electron beams. Med. Phys. 20, 1453–1455 (1993). 17. American Society of Testing Materials. Standard practice for use of the alanine-EPR dosimetry system (Standard E. 1607-96). Annual Books of ASTM Standards 798-802 (1998). 18. Roberts, J. et al. A phase III randomized study of surgery vs. surgery plus adjuvant radiation therapy in intermediate risk adenocarcinoma (GOG #99). In: Annual Meeting of the Society of Gynecologic Oncologist 70 (1998).
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maximum deviation between the measured and planned doses ranged from 22.5 to 2.1 %. In order to quantify the effect of the CT radiation on the measured dose, one L-alanine dosemeter used during the CT scan was analysed for the first patient. The spectrum obtained is shown in Figure 4. In comparison with the spectrum obtained from the 180-cGy treatment dose, the CT spectrum is negligible. Table 2 shows the results of the in vivo dosimetry data as calculated from Equation (2). For all dosemeters, the dose was calculated by the treatment planning system for the whole volume, giving an average value of dose to compare with the measured dose. For all cases, the maximum deviation of the measured from the planned dose varied from 29.2 to 14.2 %. The readout technique or the dose delivery system itself could also influence the measured results. The uncertainties include the uncertainty of the alanine/ ESR reading, around 3.5 % and the concerned to the treatment method (monitor output fluctuation of the treatment machine and dose calculation uncertainty of the treatment planning system, for example) not exceeding .2 %, one challenge was to perform the study at low doses (,2 Gy).
IN VIVO DOSE EVALUATION USING L-ALANINE/ESR DOSIMETRY 19. Creutzberg, C. L. et al. Surgery and postoperative radiotherapy versus surgery alone for patients with stage 1 endometrial carcinoma: multicentre randomized trial. Lancet 355, 1404–1411 (2000). 20. Ferrandina, G. et al. Long-term analysis of clinical outcome and complications in locally advanced cervical cancer patients administered concomitant chemoradiation followed by radical surgery. Gynecol. Oncol. 119, 404 –410 (2010). 21. Guckenberger, M. et al. Stereotactic body radiotherapy for local boost irradiation in unfavourable locally recurrent gynaecological cancer. Radiother. Oncol. 94, 53–59 (2010). 22. Mabuchi, S. Postoperative whole pelvic radiotherapy plus concurrent chemotherapy versus extended-field irradiation
for early-stage cervical cancer patients with multiple pelvic lymph node metastases. Gynecol Oncol. 120, 94– 100 (2011). 23. Mabuchi, S. et al. Radical hysterectomy with adjuvant radiotherapy versus definitive radiotherapy alone for FIGO stage IIB cervical cancer. Gynecol. Oncol. 123, 241–247 (2011). 24. Arie, A. B. et al. Temporal pattern of recurrence of stage I endometrial cancer in relation to histological risk factors. Eur. J. Surg. Oncol. 38, 166– 169 (2012). 25. Gong, L. et al. Clinical evaluation of neoadjuvant chemotherapy followed by radical surgery in the management of stage IB2-IIB cervical cancer. Inter. J.Gynecol. Obstet. 117, 23–26 (2012).
Downloaded from http://rpd.oxfordjournals.org/ at Anadolu University on May 19, 2014
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doi:10.1093/rpd/ncu128
IN VIVO DOSE EVALUATION DURING GYNAECOLOGICAL RADIOTHERAPY USING L-ALANINE/ESR DOSIMETRY Amanda Burg Rech1,*, Gustavo Lazzaro Barbi2, Luiz Henrique Almeida Ventura2, Flavio Silva Guimara˜es2, Harley Francisco Oliveira2,3 and Oswaldo Baffa1 1 Departamento de Fı´sica, FFCLRP, Universidade de Sa˜o Paulo, Ribeira˜o Preto, Sa˜o Paulo, Brasil 2 Servic¸o de Radioterapia, HCFMRP, Universidade de Sa˜o Paulo, Ribeira˜o Preto, Sa˜o Paulo, Brasil 3 Departamento de Clı´nica Me´dica, FMRP, Universidade de Sa˜o Paulo, Ribeira˜o Preto, Sa˜o Paulo, Brasil *Corresponding author: [email protected]
INTRODUCTION Gynaecological malignancies are one of the most common tumours in women, resulting in the death of several thousands of women per year(1), even though the potential for cure is high when diagnosed early(2). One of the treatments for these tumours is a 3-D external beam radiation therapy (EBRT). The efficacy of EBRT requires precise administration of the prescribed dose to the tumour with an accuracy between 25 and 7 %, as established by the International Commission on Radiation Units and Measurements (ICRU) report number 50(3). Clinical dosimetry with the alanine/electron spin resonance (ESR) readout method has been reported in the literature for different objectives(4 – 12), but not for EBRT treatment of gynaecological cancer. The widely known advantages of alanine as a dosemeter material in clinical practice are its tissue-equivalent behaviour, signal stability, independence on dose rate, and nontoxicity(13 – 17). In gynaecological malignancies, such as cervical and endometrium cancer, the vaginal wall is notoriously subject to recurrence(18 – 25), highlighting the importance of dosimetry in the tumour region. Therefore, the aim of this study is the verification of the dose administered by adjuvant 3-D EBRT in the treatment target of patients diagnosed with gynaecological cancer using L-alanine and ESR spectrometry. MATERIALS AND METHODS L-alanine
(Sigma-Aldrich) was used in powder form to avoid binder interference in the signal, and was packed into thin gel capsules with an outer diameter of 0.5 cm
and a length of 1 cm. The dosemeter was confined to the capsule volume, as defined by the treatment planning system. The capsules were stored under light and heat protection, and were kept at the same temperature and humidity conditions as that of the laboratory environment. For the ESR measurement the alanine powder was transferred to a quartz tube with a 4-mm inner diameter just before measurements. The ESR spectra of the dosemeters were recorded in an X-band spectrometer from JEOL, model JES-FA200 (9.5 GHz). The system parameters used in all studies reported herein were the same: 100-kHz frequency, 1.0-mT modulation amplitude, 15-mT scan width, 1-min scan time and 0.3-s time constant. The microwave power was 2.5 mW and the mass was 50 mg, length in the quartz tube ,1 cm, covering the high sensitivity part of the resonator cavity. To improve the signal-tonoise ratio, parameters such as the microwave power and the modulation amplitude were optimised. Since alanine dosimetry is a relative method, a calibration curve is essential to correctly relate the absorbed dose recorded by a specific equipment. Alanine detectors were irradiated with 6-MV X rays from a Siemens ONCOR Plus linear accelerator. This machine is routinely calibrated with the ionisation chamber (TRS 398 Protocol) to ensure the delivery dose in daily treatments. To obtain the calibration curve, four dosemeters at a time were irradiated. The dose was determined from the intensity of the peakto-peak amplitude of the averaged alanine spectrum. The phantom study was performed using a pelvic solid water phantom with an acrylic adapter to insert the vaginal device containing the dosemeters.
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at Anadolu University on May 19, 2014
The dose delivered by in vivo 3-D external beam radiation therapy (EBRT) was verified with L-alanine/electron spin resonance (ESR) dosimetry for patients diagnosed with gynaecological cancer. Measurements were performed with an X-band ESR spectrometer. Dosemeters were positioned inside the vaginal cavity with the assistance of an apparatus specially designed for this study. Previous phantom studies were performed using the same conditions as in the in vivo treatment. Four patients participated in this study during 20-irradiation sessions, giving 220 dosemeters to be analysed. The doses were determined with the treatment planning system, providing dose confirmation. The phantom study resulted in a deviation between 22.5 and 2.1 %, and for the in vivo study a deviation between 29.2 and 14.2 % was observed. In all cases, the use of alanine with ESR was effective for dose assessment, yielding results consistent with the values set forth in the International Commission on Radiation Units and Measurements (ICRU) reports.
A. B. RECH ET AL.
Figure 1 shows the pelvic phantom, the device used to hold the dosemeters and a schematic showing the detector distribution inside the device. To define the treatment region and dose, both for the phantom and the in vivo study, a computed tomography (CT) image was taken with a Philips Big Bore CT scanner, and the treatment planning software (TPS) XiO 4.62 from Elekta was used. The dose
RESULTS AND DISCUSSION Figure 3 shows the dose –response curve obtained for L-alanine detectors irradiated with 20– 240 cGy using a 6-MV X-ray linear accelerator. The errors bars correspond to the differences obtained from the mean value of the four dosemeters irradiated at the same dose. The dose –response curve approximates the relationship between dose and ESR signal intensity, given by the following equation: Figure 1. Pelvic solid water phantom with the acrylic adapter and the inserted device (a), the device which holds the alanine dosemeters separated by small chambers denoted by A, B and C (b). Each chamber contains capsules containing L-alanine powder (c).
D ¼ 4:00 IESR 15:48;
ð1Þ
where IESR is the ESR signal intensity normalised by the sample mass (a.u. mg21) and D the dose in cGy. The correlation coefficient is 0.99743.
Figure 2. Example of a CT image (a) and a portal image (b) showing the location of the bone reference ( pelvic symphisys) (large circles) and the radiopaque markers (small circles). The arrows relate the objects to each other, showing their respective location in each image.
Page 2 of 5
Downloaded from http://rpd.oxfordjournals.org/ at Anadolu University on May 19, 2014
prescribed was equivalent to a pelvic treatment of 180 cGy fraction21. Measurements were carried out in four patients. The prescribed dose was 4.500 cGy, divided into 25 fractions of 180 cGy, with 5 measurements taken from each patient, resulting in the analysis of 220 dosemeters. The apparatus used to put the dosemeters in the treatment region is shown in Figure 1b. Studies began after the approval of the experimental protocol by the Ethics Committee and informed consent was obtained from all patients participating in the study. Radiopaque markers were placed in the apparatus to verify its position before each of the five study sessions. For verification a portal image was taken before each measured session, using bone references to confirm the internal position and the location of the isocentre, as shown in the example in Figure 2. The dose originated from the portal image was negligible compared with the treatment one, 2 cGy. Also, the initial positioning of the markers observed in the CT image enabled the registration and analysis of the CT image with those taken on the day of treatment.
IN VIVO DOSE EVALUATION USING L-ALANINE/ESR DOSIMETRY
Table 1. Results of the phantom study: comparison between the measured and planned dose. Detector chamber
Deviation of the measured from the planned dose (%)
Figure 4. ESR spectrum obtained for a dosemeter irradiated during the CT scan and during a radiotherapy session. It is evident that no dose is detected by the dosemeter during the CT scan.
Table 2. Results of the in vivo study: comparison between the measured and planned doses. Patient
Simulation session 1
2
3
4
22.0 þ0.6 22.5
22.3 21.1 20.9
1.4 0.6 0.4
0.5 2.1 20.6
Detector chamber
Deviation of the measured from the planned dose (%) Session number 1
A B C
Each value of the chamber is a mean value of the dosemeters presented there.
1 2 3
The results of the phantom study are presented in Table 1, in which the measured dose is compared with the planned dose. For the comparison, the following equation was employed: D% ¼
DM DP DP
100 %;
ð2Þ
where DM is the measured dose, DP the planned dose and D% is the percentage difference of the measured dose relative to the planned dose. In contrast to brachytherapy, the deviations between planned and measured single-fraction doses obtained by in vivo radiotherapy dosimetry show no large dose gradient. It is important to note that for the phantom study no heterogeneity correction was employed, and this could result in errors due to the difference in density between solid water (1.00 g cm23) and polymethyl methacrylate (acrylic) (1.18 g cm23). Also, the
4
A B C A B C A B C A B C
2
3
4
5
23.7 þ5.6 þ1.2 þ4.9 þ3.1 þ2.8 20.8 24.7 23.9 þ2.2 þ3.8 25.3 25.6 þ5.0 þ4.9 þ4.2 þ1.9 20.8 þ5.9 þ5.6 þ0.7 þ1.1 þ3.8 þ1.1 þ1.9 þ4.7 þ2.6 þ1.3 þ4.1 22.3 þ14.2 þ10.8 þ3.1 28.3 þ5.6 þ8.8 þ3.3 26.1 24.4 23.6 20.8 þ1.2 20.2 29.2 22.0 þ7.4 þ8.7 þ1.4 20.3 þ9.9 þ13.2 þ6.7 21.3 þ4.2 þ9.9 þ2.3 þ4.5 21.5 20.4 þ5.9
The spaces with (2) represent cases that the region was not inside the treatment field. Presentation of the results is in the same scheme as for the phantom study in Table 1.
studies were performed in different sessions; therefore, the differences reflect errors from all aspects of the procedure from positioning to dose delivery. Table 1 shows that in most cases the results are in compliance with what was proposed by ICRU, as discussed above. The measured doses agreed well with the doses calculated by the TPS. Following the verification of the dosimetry obtained from the phantom study, an in vivo feasibility study was conducted. The
Page 3 of 5
Downloaded from http://rpd.oxfordjournals.org/ at Anadolu University on May 19, 2014
Figure 3. Dose–response curve for L-alanine detectors irradiated with 20– 240 cGy (6 MV X rays). A linear fitting was made and the outlier curves were set at +95 % of a confidence interval.
A. B. RECH ET AL.
CONCLUSIONS This work was concerned with the verification of the dose in the target volume of the vaginal dome in a 3-D EBRT treatment, especially because of the incidence of tumour recurrence in this region. The calibration curve for the L-alanine/ESR dosimetric systems was linear with the dose in the interval of 20–240 cGy, and the phantom study showed that most of the measured doses are within allowable tolerances, with deviations of 22.5 to 2.1 %. In the in vivo studies, the agreement between the measured dose and the dose calculated from treatment planning complied with that established by ICRU recommendations. Discrepancies are likely to be associated with the movement of the dosemeter probe during the radiotherapy session. ACKNOWLEDGEMENTS Thanks to the Servic¸o de Radioterapia of Hospital das Clı´nicas of FMRP-USP, and to Carlos Brunello, Lourenc¸o Rocha and Jose´ Azziani for technical assistance. FUNDING This work was partially supported by Fundac¸a˜o de Amparo a` Pesquisa do Estado de Sa˜o Paulo (FAPESP) Project 2010/12780-2, Coordenac¸a˜o de Aperfeic¸oamento de Pessoal de Nı´vel Superior (CAPES) and Conselho Nacional de Desenvolvimento Tecnolo´gico (CNPq).
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maximum deviation between the measured and planned doses ranged from 22.5 to 2.1 %. In order to quantify the effect of the CT radiation on the measured dose, one L-alanine dosemeter used during the CT scan was analysed for the first patient. The spectrum obtained is shown in Figure 4. In comparison with the spectrum obtained from the 180-cGy treatment dose, the CT spectrum is negligible. Table 2 shows the results of the in vivo dosimetry data as calculated from Equation (2). For all dosemeters, the dose was calculated by the treatment planning system for the whole volume, giving an average value of dose to compare with the measured dose. For all cases, the maximum deviation of the measured from the planned dose varied from 29.2 to 14.2 %. The readout technique or the dose delivery system itself could also influence the measured results. The uncertainties include the uncertainty of the alanine/ ESR reading, around 3.5 % and the concerned to the treatment method (monitor output fluctuation of the treatment machine and dose calculation uncertainty of the treatment planning system, for example) not exceeding .2 %, one challenge was to perform the study at low doses (,2 Gy).
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