Physica Medica 30 (2014) 432e436
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Original paper
Effective dose in percutaneous transhepatic biliary drainage examination using PCXMC2.0 and MCNP5 Monte Carlo codes E. Karavasilis a, *, A. Dimitriadis a, H. Gonis c, P. Pappas b, E. Georgiou a, E. Yakoumakis a a
Medical Physics Department, Medical School, University of Athens, 75 Mikras Asias Str., Goudi, 11527 Athens, Greece Radiology Department, Laiko Hospital of Athens, 17 Ag. Thoma Str., Goudi, 11527 Athens, Greece c Medical Physics Department, Laiko Hospital of Athens, 17 Ag. Thoma Str., Goudi, 11527 Athens, Greece b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 July 2013 Received in revised form 9 December 2013 Accepted 10 December 2013 Available online 25 December 2013
Objectives: To estimate the organ equivalent doses and the effective doses (E) in patient undergoing percutaneous transhepatic biliary drainage (PTBD) examinations, using the MCNP5 and PCXMC2 Monte Carlo-based codes. Methods: The purpose of this study is to estimate the organ doses to patients undergoing PTBD examinations by clinical measurements and Monte Carlo simulation. Dose area products (DAP) values were assessed during examination of 43 patients undergoing PTBD examination separated into groups based on the gender and the dimensions and location of the beam. Results: Monte Carlo simulation of photon transport in male and female mathematical phantoms was applied using the MCNP5 and PCXMC2 codes in order to estimate equivalent organ doses. Regarding the PTBD examination the organ receiving the maximum radiation dose was the lumbar spine. The mean calculated HT for the lumbar spine using the MCNP5 and PCXMC2 methods respectively, was 117.25 mSv and 131.7 mSv, in males. The corresponding doses were 139.45 mSv and 157.1 mSv respectively in females. The HT values for organs receiving considerable amounts of radiation during PTBD examinations were varied between 0.16% and 73.2% for the male group and between 1.10% and 77.6% for the female group. E in females and males using MCNP5 and PCXMC2.0 was 5.88 mSv and 6.77 mSv, and 4.93 mSv and 5.60 mSv. Conclusion: The doses remain high compared to other invasive operations in interventional radiology. There is a reasonable good coincidence between the MCNP5 and PCXMC2.0 calculation for most of the organs. Ó 2013 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
Keywords: Dose assessment Monte Carlo Modeling Radiology
Introduction Effective (E) and equivalent (HT) doses are measurements of the cancer risk to a whole or part of organism due to ionizing radiation delivered non-uniformly to part(s) of its body, in radiation protection and radiology. The usage of X-ray for diagnostics and interventional procedures is a significant cause of radiation exposure among the population. Therefore, the calculated radiation burden of the patients and the employees contributes to the improvement of the techniques that are routinely applied. Moreover, the radiation risk of employees, such as hand’s radiation burden, is related to the patient radiation exposure [1]. Percutaneous transhepatic biliary drainage (PTBD) is a procedure used to drain the bile ducts in the presence of a blockage or damage that prevents normal bile drainage. In this study the drainage restitution was performed using stents. * Corresponding author. Tel.: þ30 2107462372, þ30 6973618156. E-mail address: [email protected] (E. Karavasilis).
Organ doses and HT are difficult to be measured directly so, conversion factors which relate equivalent dose to measurable quantities such as the dose area product (DAP) [2e16] must therefore be employed. The Monte Carlo simulation is a widespread calculation method that has been used in organ dose dosimetry combined with measurements that are recorded during the procedure [3,11,13e15,17e23]. The complexity of PTBD procedures demands considered radiation exposure time. The aim of this study is the estimation of patients’ radiation burden undergoing PTBD procedures, using Monte Carlo codes, for the assessment of radiation risk, since there are limited data in the literature. Two Monte Carlo codes were used in order to achieve valid results and to compare the two methods. Material and methods A total number of forty three patients who underwent PTBD procedures in the Radiological Imaging Department of Laiko Hospital of Greece were included in this study. Twenty three patients
1120-1797/$ e see front matter Ó 2013 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ejmp.2013.12.003
E. Karavasilis et al. / Physica Medica 30 (2014) 432e436
were females and twenty males. During the procedure patients were in supine orientation while the X-ray tube was under the back of them. A flexible guidewire is inserted through a tiny hole in the skin and then is fluoroscopically guided carefully into the bile ducts. Then a catheter is threaded onto the guidewire, and a small mass of contrast agent is injected, during the assay of interventional radiologist to place the catheter to the point of drainage. Owing to the stenosis or blockages of the bile ducts, the guidance of catheter is especially hard. Because of that, it was necessary to use angiographic images of the monitor in order to manipulate the catheter to reach the drainage point. The irradiated region was changing and whenever the interventional radiologist considered that it was useful to minimize the radiation burden, collimation was performed. During the procedure patient data (gender, age, body characteristics) and technical parameters for each examination studied were recorded. The technical settings used for the selected procedures were, the dimensions of the monitor irradiated area, the distances between the source and patient and between the table top and the floor, the irradiation angles, tube voltage, the radiographic and fluoroscopy time, dose area product (DAP) measurement values [24]. Field dimensions and field sizes at patient entrance surface were calculated using the following technique. A grid was placed at a specific distance from the X-ray source and the image amplifier. It was irradiated using image magnification (image intensifier 40 cm, zoom 28, 20, 14 cm). Then we had to scale from a known distance. The sample was divided into two subgroups by the gender, and then the projections were divided into 14 and 11 categories based on the dimensions and the location of field of view (FOV) for the females and males, respectively (Table 1). All procedures were performed on a monoplane digital c-arm (Multistar, Siemens) with a high frequency generator (Polydoros ISA) a Megalix tube 40/82 and a Sireian 40-4 HDR image intensifier. The system is equipped with an internal DAP meter (Diamentor KP, PTW, Freiburg, Germany) that provides a readout of the cumulative DAP values, along with the skin dose at a reference distance of 55 cm from the tube focus. It has been calibrated in accordance with the German standards (DIN 6819) against a reference instrument (DIN 6817) calibrated by the Physikalisch-Technische Bundesanstalt. The calibration of the instrument has been formally verified by the secondary standard dosimetry laboratory of the Greek Atomic Energy Commission. The PTBD procedures were simulated using two Monte Carlo codes MCNP5 and PCXMC2.0. The simulation of patients was based
Table 1 Dimensions of FOV in each category. Category
Males
1 2 3 4 5 6 7 8 9 10 11 12 13 14
13.35 17.59 13.70 18.76 10.51 15.95 7.44 10.38 8.28 22.32 16.28
Females
Dimensions (cm cm)
1.06 0.44 0.88 1.77 0.95 0.80 1.17 0.52 1.06 0.00 0.00
17.42 18.22 13.93 23.23 11.20 16.88 9.53 16.57 14.29 22.92 28.35
Dimensions (cm cm)
0.97 0.93 0.77 1.67 1.06 0.88 1.47 0.53 0.41 0.00 0.00
13.99 16.81 13.48 18.34 10.31 15.60 7.72 19.35 11.84 9.00 11.60 14.88 25.09 28.45
0.82 0.30 0.76 1.39 1.22 0.74 0.89 0.25 2.21 0.86 0.23 1.56 0.84 1.31
17.87 18.33 13.82 22.50 10.93 16.87 8.15 18.04 19.39 13.52 13.49 11.47 26.25 27.93
0.84 1.07 0.68 2.03 1.32 0.97 0.98 1.53 0.28 1.00 0.97 0.95 2.21 0.83
433
on the ORNL MIRD and Cristy Eckerman mathematical hermaphrodite phantom models [25e27]. The Monte Carlo codes MCNP5 from Los Alamos laboratory [28] and afterward the PCXMC2.0 were used. The cross-section libraries involved in the present simulations using MCNP5 code were ENDF/B-VI8. The hermaphroditic ORNL phantoms were modified to the male and female gender for the simulation. The removed organs were the breasts and the uterus for the male version and the testes and genitalia for the female version. Because the MIRD phantom does not allow separation of cortical bone and bone marrow, the irradiation of the latter was not evaluated. Measurements were performed based on the hypothesis that the radiation dose of the bone marrow is associated with the percentage of volume of the bone marrow in the total bone [25,29]. The X-ray spectrum used was derived from the SRS-78 software code [30]. The energy spectrum was described in discrete values produced as average values of intervals of 1 keV, taking into account the applied kVp, the anode angle, the total filtration of the tube and the ripple of voltage, for each projection. The desirable size and point of the FOV to the patient was achieved using a simulated collimation structure. The distance between the focus and the entrance plane of the simulated DAP meter was 30 cm. An f2 tally was used to score as the particle fluence going through the beam’s cross-section at the location of the internal DAP meter. The obtained result was then converted to absorbed dose in Gy per starting photon, which is numerically equal to air kerma, using fluence-to-air-dose conversion function as tabulated by the ICRP 51 [31]. Finally DAP value per starting photon was yielded by a multiplication of Gy per starting photon by the beam area at the position of DAP. The normalized to DAP organ doses in mGy per starting photon (and consecutively the HT in mSv per starting photon) were calculated by using the MCNP5 f6 tally in each category, as is commonly used [19,20,32,33]. Organ doses of each category were multiplied with the corresponding DAP values. The number of starting particles involved in each simulation was 4 108. The simulation time was about 600 min using an Intel T7250 Core duo processor of 2 þ 2 GHz CPU and 2 GB RAM. Monte Carlo code, PCXMC2.0, uses anatomical data that are based on the computational hermaphrodite phantom models specified by Cristy and Eckerman [26], modified by PCXMC. The Xray spectra are simulated based on the Birch and Marshal [34], theory and was modulated according to the X-ray tube voltage, the angle of the tungsten target and the filtration. The organ doses are related to the exposure area product (DAP) of each projection. PCXMC allows the free adjustment of the geometry of the irradiation. The same geometrical parameter like the position of the point source, the distance between the source and the patient and the field dimensions, as well as the irradiation parameters like the tube voltage and the total filtration, were used for each projection with the corresponding simulation of MCNP5 in order to verify and compare the calculated results. The simulation was terminated when 2 107 starting particles (photons) interacted with the phantom. The simulation time was about 60 min using an Intel T7250 Core duo processor of 2 þ 2 GHz CPU and 2 GB RAM. The total HT was estimated using the sum of the equivalent doses of n projections, HT,i during each procedure.
HT ¼
n X
HT;i
(1)
i¼1
The E was calculated as the sum of the HT’s multiplied by the weighting tissue factors (WT) according to ICRP 103 [35].
E ¼
X T
WT HT;i
(2)
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Finally, PCXMC2.0 calculate the risk of exposure cancer death (REID) using the dose and the dose rate effectiveness factor of 1.5 [22]. The comparison between groups (male, female) or methods (PCXMC2.0, MCNP5) was performed calculating the percentage deviation PD%.
i h 100 PD% ¼ ðxi yi Þ z1 i
(3)
where xi and yi were the comparison’s values of each group or method and zi the mean value of them. Results Monte Carlo simulation of photon transport in twenty male and twenty three female patients who underwent PTBD procedure was applied using MCNP5 and PCXMC2 codes. The mean DAP values were 4500 2600 cGycm2 and 5500 3300 cGycm2, the median DAP values were 4500 cGycm2 and 4800 cGycm2 and the mean total radiographic and fluoroscopic times were 13.5 12.6 min and 13.9 9.5 min for males and females, respectively.
Table 3 Calculated equivalent organ doses for male group using PCXMC2.0 code. Organs/tissue
Liver Pancreas Adrenals Kidneys Stomach Lungs Spleen Ribs Small intestine Skin Lower spine Mid spine Colon large intestine Esophagus Muscle Upper large intestine Breasts Bone marrow Total eff. dose
Males
Females
Pd%
Mean (mSv)
Median (mSv)
Mean (mSv)
24.92 19.65 12.05 8.57 52.79 34.82 72.41 51.41 2.51 2.39 2.94 2.52 2.49 3.03 28.34 22.33 7.84 6.37 3.96 3.30 131.7 108.9 33.53 25.41 4.87 4.30
19.92 8.52 41.78 49.82 1.72 1.88 1.25 20.13 66.6 2.85 103.4 25.72 3.95
30.10 13.80 60.14 87.25 3.35 3.41 3.70 37.23 7.93 5.12 157.1 40.52 5.38
3.65 3.05 4.67 3.48 9.15 7.22
2.58 3.13 6.74
e 8.23 6.91 5.60 4.51
e 5.59 4.30
18.14 9.04 36.41 54.45 2.66 2.16 4.29 21.82 6.34 3.36 110.7 24.65 4.02
Median (mSv) 27.12 11.70 57.07 79.15 2.40 3.53 1.79 35.82 6.72 4.23 149.8 38.35 5.15
18.8 13.5 13.0 18.6 28.8 14.8 39.2 27.1 1.2 25.5 17.6 18.9 10.0
4.24 2.81 5.18 3.35 9.03 6.70
3.72 4.34 8.83
15.1 10.5 1.2
0.48 0.30 10.52 6.89 6.77 4.23
0.47 9.23 5.82
e 24.4 e
Comparison between male and female groups The mean and median calculated HT values for the organs receiving considerable amounts of radiation doses and E values in the female and male group using the MCNP5 and PCXMC2 codes are given in Tables 2 and 3, respectively. The median values were calculated in order to consider the distribution of the sample. The f2 tallies of MCNP5 code passed all the statistical and errors checks and the relative errors were less than 0.1%. The calculated relative errors were lower than 0.3% for the most irradiated organs and lower than 2% for the less irradiated organs. The corresponding value concerning the organs that were distal from the actual beam was less than 7%, because in that case the amount of photons reaching the organs was small. The average percentage deviations of all organs between the two groups were 17.2% and 16.5% using the MCNP5 and PCXMC2, respectively. The deviation between the mean and median value
was statistically significant, hence the distribution of the sample was not a normal distribution. Comparison between two Monte Carlo codes The calculated HT values for the organs receiving considerable amounts of radiation doses, in both female and male group using the MCNP5 and PCXMC2.0 Monte Carlo codes are presented through the histogram of Fig. 1. The Pd% of the values in Fig. 1 are presented in Table 4. Risk estimation The REID, that have arisen from the PCXMC2.0 dose results are given in Table 5 for the female and male group. The mean age was 60 years old for both groups. Discussion
Table 2 Calculated HT for female and male group using MCNP5 code. Organs/tissue
Females
Males
Mean (mSv) Liver Pancreas Adrenals Kidneys Stomach Lungs Spleen Ribs Small intestine Skin Lower spine Mid spine Colon large intestine Esophagus Muscle Upper large intestine Breasts Bone marrow Total eff. dose
29.77 12.54 61.24 91.30 2.87 3.14 3.25 32.72 7.24 5.16 139.45 33.59 4.94
17.93 8.24 37.11 56.89 2.33 2.00 3.89 22.61 5.84 3.37 112.63 24.36 3.70
Pd%
Median (mSv)
Mean (mSv)
Median (mSv)
26.89 10.49 56.24 82.88 2.05 3.22 1.63 37.75 6.17 4.24 149.8 37.46 4.73
24.76 19.54 10.98 7.81 52.71 34.42 75.56 53.59 2.14 2.09 2.74 2.38 2.14 2.72 24.83 23.27 7.23 5.88 3.99 3.32 117.25 110.53 27.97 25.23 4.53 4.00
19.63 7.88 42.16 51.54 1.46 1.77 1.05 21.19 5.16 2.88 105.38 25.74 3.71
18.4 13.3 15.0 18.9 29.3 13.5 41.1 27.4 0.1 25.5 17.3 18.3 8.7
3.76 2.51 6.03 3.87 8.33 6.21
3.28 5.06 8.14
3.26 2.75 5.43 4.03 8.54 6.74
2.33 3.65 6.36
14.2 10.5 2.5
0.44 0.27 4.64 2.99 5.88 3.66
0.45 4.26 5.19
e 3.82 3.06 4.92 3.94
e 2.91 3.81
e 19.4 e
Monte Carlo simulation was used in conjunction with DAP measurements to estimate the organ doses. Uncertainties during the estimation of HT apart from normal measurement errors are also related to patient displacements, variable patient anatomy, geometrical and substantial differences between the patients and the used mathematical phantoms for the derivation of the dose conversion coefficients. Larger deviations were found during the estimation of the HT in concerning the organs located outside the primary X-ray field or in the end of the beam. The organs receiving considerable amounts of radiation doses were the lumbar spine, the kidneys and the adrenals, for both genders. The respective HT values were 157.1 110.7 mSv, 87.25 54.45 mSv and 60.14 36.41 mSv, for the female group and 131.7 108.9 mSv, 72.41 51.41 mSv and 52.79 34.82 mSv for the male group using PCXMC2.0 code. These organs were located in the irradiated field of view for the majority of the projections. The large standard deviations of HT were due to the procedure’s complexity and the rarity. A significant difference is obvious in the values of HT (Tables 2 and 3) for female and male groups, for both codes. The percentage deviations varied between 1.2% and 39.2%, for PCXMC2.0 code, and between 0.1% and 41.1% for MCNP5 code.
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Figure 1. Histogram of mean HT for the male and female group using MCNP5 and PCXMC2.0 codes.
The HT values were calculated for phantoms with standard dimensions. The actual patient thickness is a significant factor for the organ dose assessment, especially when the patient differs significantly from the standard patient phantom. It must be pointed out that while any changes in the phantom dimensions (height, mass) were allowed using the PCXMC2.0 code, the same process was quite difficult for the phantom of MCNP5 code in clinical routine. The DAP values in this study, were 4500 2600 cGycm2 and 5500 3300 cGycm2, in males and females, respectively. These values were comparable to the reported diagnostic reference levels, 5400 cGycm2 in biliary drainage and 5000 cGycm2 in biliary intervention [36]. In the NRPB-W14 the mean and the ranges of reported DAP values of 202 biliary drainage procedures were 3400 cGycm2, and 7100e9320 cGycm2, and in 182 biliary interventions were 4000 cGycm2 and 1900e10,000 cGycm2, respectively [37]. In our study the mean DAP values were in the range but
Table 4 Calculated Pd% between two codes per gender group. Organs/tissue
Females Pd%
Males Pd%
Liver Pancreas Adrenals Kidneys Stomach Lungs Spleen Ribs Small intestine Skin Lower spine Mid spine Colon large intestine Esophagus Muscle Upper large intestine Breasts Bone marrow
1.1 9.5 1.8 4.5 15.2 8.1 13.2 12.9 9.1 0.8 11.9 18.7 8.6 12.0 15.1 8.1 7.8 77.6
0.7 9.3 0.2 4.2 15.7 6.8 15.1 13.2 8.0 0.8 11.6 18.1 7.3 11.1 15.1 6.9 e 73.2
higher than the reported values of NRPB-W-14. The higher DAP values can be explained by the complexity of the procedure. The total radiographic and fluoroscopic times were 13.5 12.6 min and 13.9 9.5 min in males and females, respectively, comparable to the 13.35 min, which was the fluoroscopic time reported in NRPB-W14. The radiation exposure is related to deterministic and stochastic effects. The most critical deterministic effect, in interventional radiology, is temporary skin erythema or skin injury. The estimated threshold for radiation damage in skin is about 2 Gy. From Tables 2 and 3 deviating with the WT, we can calculate that the radiation exposure of the whole skin was about 5 mGy and 4 mGy using the both codes, for the female and male group, respectively. The most critical stochastic effect is cancer development that will result in death. The REID values that were presented in Table 5, were significant low. However, the higher values of REID are related with the possibility of lung cancer for women (0.000754%) and leukemia (0.000661% and 0.000664%), for the female and male group respectively, that was expected due to significant radiation burden of bone marrow. PCXMC2.0 don’t calculate the REID of breast cancer on males. The values of REID were lower than the corresponding values to other causes for mortality [38]. Cancer mortality for other reasons was 22.2% and 18.6%, as was calculated from PCXMC2.0 code, for males and females 60 years old, respectively. From Fig. 1 we can conclude that there was a rather good coincidence agreement between the results produced by the two Table 5 Calculated REID% per gender group for the induction of specific cancer types. Cancer type
Females REID
Males REID
Leukemia Breast cancer Colon cancer Liver cancer Lung cancer Stomach cancer Bladder cancer
0.000661% 7.75E6% 0.000197% 0.000109% 0.000754% 0.000104% 7.52E7%
0.000664% e 0.000278% 0.00013% 0.000317% 5.77E5% 6.00E7%
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Monte Carlo codes. The HT values for the organs receiving considerable amounts of radiation doses were varied, 0.16e73.2% for the male group and 1.10e77.6% for the female group. The major differences between the two code’s calculations were the HT values of the bone marrow. This is due to the difference in bone modeling between the two used phantoms and the subsequent different estimation of the bone marrow equivalent to doses for each of the two used codes. The results show that PCXMC2.0 software yields values larger than those produced by Monte Carlo method based on MCNP5 code. The accuracy and the reliability of the two codes have been proved. Both codes yield similar dose distributions over the body, as it is presented in Fig. 1. Conclusion Monte Carlo simulation (MCNP5 and PCXMC2.0 codes) was used in conjunction with DAP measurements in order to estimate both HT and E for patients undergoing PTBD examinations. The organs receiving the highest amounts of doses during these exams are lumbar spine, adrenals and kidneys for both genders. Moreover high values of REID are related to the possibility of lung cancer for women and leukemia for both women and men. Comparison of MCNP5 and PCXMC2.0 simulation results demonstrated that the percentage deviations were about to 10% in the most of organs. Taking into the account that PCXMC2.0 code’s simulation time was 60 min, ten times lower than the correspondence MCNP5, PCXMC2.0 can be used in clinical routine. However, further investigation is needed in order to decrease the radiation dose according to the ALARA principle. Medical staff should be aware of all technical parameters that might contribute to reduction of radiation exposure as far as the setting and review of reference dose values. Finally, quality control of the equipment will further optimize value of PTDB exams. References [1] Damilakis J, Koukourakis M, Hatjidakis A, Karabekios S, Gourtsoyiannis N. Radiation exposure to the hands of operators during angiographic procedures. Eur J Radiol 1995;21:72e5. ar T, Toklu T, Cag lan A, Onal E, Padovani R. Patient doses and [2] Bor D, Olg dosimetric evaluations in interventional cardiology. Phys Med 2009;25:31e 42. [3] Bozkurt A, Bor D. Simultaneous determination of equivalent dose to organs and tissues of the patient and of the physician in interventional radiology using Monte Carlo method. Phys Med Biol 2007;52:317e30. [4] Burcharth F, Nielbo N. Percutaneous transhepatic cholangiography with selective catheterization of the common bile duct. Am J Roentgenol 1976;127: 409e12. [5] Hart D, Hillier MC, Wall BF. Doses to patients from medical X-ray examinations in the UK. Review, NRPB-W14. Available at: http://www.hpa.org.uk/ webc/HPAwebFile/HPAweb_C/1194947421571; 2000. [6] Noto K, Matsubara K, Koshida K, Iida H, Yamamoto T. Evaluation of patient dosed due to fluoroscopic exposures. Radiat Prot Dosim 2011;146:234e6. [7] Laufer U, Kirchner J, Kickuth R, Adams S, Jendreck M, Liermann D. A comparative study of CT fluoroscopy combined with fluoroscopy versus fluoroscopy alone for percutaneous transhepatic biliary drainage. Cardiovasc Intervent Radiol 2001;24:240e4. [8] Le Heron JC. Estimation of effective dose to the patient during medical X-ray examinations from measurements of the dose-area product. Phys Med Biol 1992;37:2117e26. [9] Majewska N, Stanisi c MG, Klos MA, Makalowski M, Frankiewicz M, Juszkat R, et al. Patients’ radiation doses during thoracic stent-graft implantation: the problem of long-lasting procedures. Ann Thorac Surg 2012;93:465e72. [10] Neocleous A, Yakoumakis E, Gialousis G, Dimitriadis A, Yakoumakis N, Georgiou E. Dosimetry using Gafchromic XR-RV2 radiochromic films in interventional radiology. Radiat Prot Dosim 2011;147:78e82. [11] Olgar T, Bor D, Berkmen G, Yazar T. Patient and staff doses for some complex x-ray examinations. J Radiol Prot 2009;29:393e407.
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[33] Stratakis J, Damilakis J, Tsetis D, Gourtsoyiannis N. Radiation dose and risk from fluoroscopically guided percutaneous transluminal angioplasty and stenting in the abdominal region. Eur Radiol 2007;17:2359e67. [34] Birch R, Marshall M. Computation of bremsstrahlung X-ray spectra and comparison with spectra measured with a Ge(Li) detector. Phys Med Biol 1979:24. [35] International Commission on Radiological Protection (ICRP). Recommendations of the international commission on radiological protection. Elsevier; 2006. Publication 103. [36] Medical Council. Diagnostic reference levels. Available at: http://www. medicalcouncil.ie/About-Us/Legislation/Medical-Ionising-Radiation/ Diagnostic-Referance-Levels-03-12-2004.pdf; 2004. [37] Hart D, Hillier MC, Wall BF. Doses to patients from medical x-ray examinations in the UK. Review, NRPB-W14. Available at: http://www.hpa.org.uk/ webc/HPAwebFile/HPAweb_C/1194947421571; 2000. [38] Cancer Research UK. Cancer mortality in the UK in 2010. 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Original paper
Effective dose in percutaneous transhepatic biliary drainage examination using PCXMC2.0 and MCNP5 Monte Carlo codes E. Karavasilis a, *, A. Dimitriadis a, H. Gonis c, P. Pappas b, E. Georgiou a, E. Yakoumakis a a
Medical Physics Department, Medical School, University of Athens, 75 Mikras Asias Str., Goudi, 11527 Athens, Greece Radiology Department, Laiko Hospital of Athens, 17 Ag. Thoma Str., Goudi, 11527 Athens, Greece c Medical Physics Department, Laiko Hospital of Athens, 17 Ag. Thoma Str., Goudi, 11527 Athens, Greece b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 July 2013 Received in revised form 9 December 2013 Accepted 10 December 2013 Available online 25 December 2013
Objectives: To estimate the organ equivalent doses and the effective doses (E) in patient undergoing percutaneous transhepatic biliary drainage (PTBD) examinations, using the MCNP5 and PCXMC2 Monte Carlo-based codes. Methods: The purpose of this study is to estimate the organ doses to patients undergoing PTBD examinations by clinical measurements and Monte Carlo simulation. Dose area products (DAP) values were assessed during examination of 43 patients undergoing PTBD examination separated into groups based on the gender and the dimensions and location of the beam. Results: Monte Carlo simulation of photon transport in male and female mathematical phantoms was applied using the MCNP5 and PCXMC2 codes in order to estimate equivalent organ doses. Regarding the PTBD examination the organ receiving the maximum radiation dose was the lumbar spine. The mean calculated HT for the lumbar spine using the MCNP5 and PCXMC2 methods respectively, was 117.25 mSv and 131.7 mSv, in males. The corresponding doses were 139.45 mSv and 157.1 mSv respectively in females. The HT values for organs receiving considerable amounts of radiation during PTBD examinations were varied between 0.16% and 73.2% for the male group and between 1.10% and 77.6% for the female group. E in females and males using MCNP5 and PCXMC2.0 was 5.88 mSv and 6.77 mSv, and 4.93 mSv and 5.60 mSv. Conclusion: The doses remain high compared to other invasive operations in interventional radiology. There is a reasonable good coincidence between the MCNP5 and PCXMC2.0 calculation for most of the organs. Ó 2013 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
Keywords: Dose assessment Monte Carlo Modeling Radiology
Introduction Effective (E) and equivalent (HT) doses are measurements of the cancer risk to a whole or part of organism due to ionizing radiation delivered non-uniformly to part(s) of its body, in radiation protection and radiology. The usage of X-ray for diagnostics and interventional procedures is a significant cause of radiation exposure among the population. Therefore, the calculated radiation burden of the patients and the employees contributes to the improvement of the techniques that are routinely applied. Moreover, the radiation risk of employees, such as hand’s radiation burden, is related to the patient radiation exposure [1]. Percutaneous transhepatic biliary drainage (PTBD) is a procedure used to drain the bile ducts in the presence of a blockage or damage that prevents normal bile drainage. In this study the drainage restitution was performed using stents. * Corresponding author. Tel.: þ30 2107462372, þ30 6973618156. E-mail address: [email protected] (E. Karavasilis).
Organ doses and HT are difficult to be measured directly so, conversion factors which relate equivalent dose to measurable quantities such as the dose area product (DAP) [2e16] must therefore be employed. The Monte Carlo simulation is a widespread calculation method that has been used in organ dose dosimetry combined with measurements that are recorded during the procedure [3,11,13e15,17e23]. The complexity of PTBD procedures demands considered radiation exposure time. The aim of this study is the estimation of patients’ radiation burden undergoing PTBD procedures, using Monte Carlo codes, for the assessment of radiation risk, since there are limited data in the literature. Two Monte Carlo codes were used in order to achieve valid results and to compare the two methods. Material and methods A total number of forty three patients who underwent PTBD procedures in the Radiological Imaging Department of Laiko Hospital of Greece were included in this study. Twenty three patients
1120-1797/$ e see front matter Ó 2013 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ejmp.2013.12.003
E. Karavasilis et al. / Physica Medica 30 (2014) 432e436
were females and twenty males. During the procedure patients were in supine orientation while the X-ray tube was under the back of them. A flexible guidewire is inserted through a tiny hole in the skin and then is fluoroscopically guided carefully into the bile ducts. Then a catheter is threaded onto the guidewire, and a small mass of contrast agent is injected, during the assay of interventional radiologist to place the catheter to the point of drainage. Owing to the stenosis or blockages of the bile ducts, the guidance of catheter is especially hard. Because of that, it was necessary to use angiographic images of the monitor in order to manipulate the catheter to reach the drainage point. The irradiated region was changing and whenever the interventional radiologist considered that it was useful to minimize the radiation burden, collimation was performed. During the procedure patient data (gender, age, body characteristics) and technical parameters for each examination studied were recorded. The technical settings used for the selected procedures were, the dimensions of the monitor irradiated area, the distances between the source and patient and between the table top and the floor, the irradiation angles, tube voltage, the radiographic and fluoroscopy time, dose area product (DAP) measurement values [24]. Field dimensions and field sizes at patient entrance surface were calculated using the following technique. A grid was placed at a specific distance from the X-ray source and the image amplifier. It was irradiated using image magnification (image intensifier 40 cm, zoom 28, 20, 14 cm). Then we had to scale from a known distance. The sample was divided into two subgroups by the gender, and then the projections were divided into 14 and 11 categories based on the dimensions and the location of field of view (FOV) for the females and males, respectively (Table 1). All procedures were performed on a monoplane digital c-arm (Multistar, Siemens) with a high frequency generator (Polydoros ISA) a Megalix tube 40/82 and a Sireian 40-4 HDR image intensifier. The system is equipped with an internal DAP meter (Diamentor KP, PTW, Freiburg, Germany) that provides a readout of the cumulative DAP values, along with the skin dose at a reference distance of 55 cm from the tube focus. It has been calibrated in accordance with the German standards (DIN 6819) against a reference instrument (DIN 6817) calibrated by the Physikalisch-Technische Bundesanstalt. The calibration of the instrument has been formally verified by the secondary standard dosimetry laboratory of the Greek Atomic Energy Commission. The PTBD procedures were simulated using two Monte Carlo codes MCNP5 and PCXMC2.0. The simulation of patients was based
Table 1 Dimensions of FOV in each category. Category
Males
1 2 3 4 5 6 7 8 9 10 11 12 13 14
13.35 17.59 13.70 18.76 10.51 15.95 7.44 10.38 8.28 22.32 16.28
Females
Dimensions (cm cm)
1.06 0.44 0.88 1.77 0.95 0.80 1.17 0.52 1.06 0.00 0.00
17.42 18.22 13.93 23.23 11.20 16.88 9.53 16.57 14.29 22.92 28.35
Dimensions (cm cm)
0.97 0.93 0.77 1.67 1.06 0.88 1.47 0.53 0.41 0.00 0.00
13.99 16.81 13.48 18.34 10.31 15.60 7.72 19.35 11.84 9.00 11.60 14.88 25.09 28.45
0.82 0.30 0.76 1.39 1.22 0.74 0.89 0.25 2.21 0.86 0.23 1.56 0.84 1.31
17.87 18.33 13.82 22.50 10.93 16.87 8.15 18.04 19.39 13.52 13.49 11.47 26.25 27.93
0.84 1.07 0.68 2.03 1.32 0.97 0.98 1.53 0.28 1.00 0.97 0.95 2.21 0.83
433
on the ORNL MIRD and Cristy Eckerman mathematical hermaphrodite phantom models [25e27]. The Monte Carlo codes MCNP5 from Los Alamos laboratory [28] and afterward the PCXMC2.0 were used. The cross-section libraries involved in the present simulations using MCNP5 code were ENDF/B-VI8. The hermaphroditic ORNL phantoms were modified to the male and female gender for the simulation. The removed organs were the breasts and the uterus for the male version and the testes and genitalia for the female version. Because the MIRD phantom does not allow separation of cortical bone and bone marrow, the irradiation of the latter was not evaluated. Measurements were performed based on the hypothesis that the radiation dose of the bone marrow is associated with the percentage of volume of the bone marrow in the total bone [25,29]. The X-ray spectrum used was derived from the SRS-78 software code [30]. The energy spectrum was described in discrete values produced as average values of intervals of 1 keV, taking into account the applied kVp, the anode angle, the total filtration of the tube and the ripple of voltage, for each projection. The desirable size and point of the FOV to the patient was achieved using a simulated collimation structure. The distance between the focus and the entrance plane of the simulated DAP meter was 30 cm. An f2 tally was used to score as the particle fluence going through the beam’s cross-section at the location of the internal DAP meter. The obtained result was then converted to absorbed dose in Gy per starting photon, which is numerically equal to air kerma, using fluence-to-air-dose conversion function as tabulated by the ICRP 51 [31]. Finally DAP value per starting photon was yielded by a multiplication of Gy per starting photon by the beam area at the position of DAP. The normalized to DAP organ doses in mGy per starting photon (and consecutively the HT in mSv per starting photon) were calculated by using the MCNP5 f6 tally in each category, as is commonly used [19,20,32,33]. Organ doses of each category were multiplied with the corresponding DAP values. The number of starting particles involved in each simulation was 4 108. The simulation time was about 600 min using an Intel T7250 Core duo processor of 2 þ 2 GHz CPU and 2 GB RAM. Monte Carlo code, PCXMC2.0, uses anatomical data that are based on the computational hermaphrodite phantom models specified by Cristy and Eckerman [26], modified by PCXMC. The Xray spectra are simulated based on the Birch and Marshal [34], theory and was modulated according to the X-ray tube voltage, the angle of the tungsten target and the filtration. The organ doses are related to the exposure area product (DAP) of each projection. PCXMC allows the free adjustment of the geometry of the irradiation. The same geometrical parameter like the position of the point source, the distance between the source and the patient and the field dimensions, as well as the irradiation parameters like the tube voltage and the total filtration, were used for each projection with the corresponding simulation of MCNP5 in order to verify and compare the calculated results. The simulation was terminated when 2 107 starting particles (photons) interacted with the phantom. The simulation time was about 60 min using an Intel T7250 Core duo processor of 2 þ 2 GHz CPU and 2 GB RAM. The total HT was estimated using the sum of the equivalent doses of n projections, HT,i during each procedure.
HT ¼
n X
HT;i
(1)
i¼1
The E was calculated as the sum of the HT’s multiplied by the weighting tissue factors (WT) according to ICRP 103 [35].
E ¼
X T
WT HT;i
(2)
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E. Karavasilis et al. / Physica Medica 30 (2014) 432e436
Finally, PCXMC2.0 calculate the risk of exposure cancer death (REID) using the dose and the dose rate effectiveness factor of 1.5 [22]. The comparison between groups (male, female) or methods (PCXMC2.0, MCNP5) was performed calculating the percentage deviation PD%.
i h 100 PD% ¼ ðxi yi Þ z1 i
(3)
where xi and yi were the comparison’s values of each group or method and zi the mean value of them. Results Monte Carlo simulation of photon transport in twenty male and twenty three female patients who underwent PTBD procedure was applied using MCNP5 and PCXMC2 codes. The mean DAP values were 4500 2600 cGycm2 and 5500 3300 cGycm2, the median DAP values were 4500 cGycm2 and 4800 cGycm2 and the mean total radiographic and fluoroscopic times were 13.5 12.6 min and 13.9 9.5 min for males and females, respectively.
Table 3 Calculated equivalent organ doses for male group using PCXMC2.0 code. Organs/tissue
Liver Pancreas Adrenals Kidneys Stomach Lungs Spleen Ribs Small intestine Skin Lower spine Mid spine Colon large intestine Esophagus Muscle Upper large intestine Breasts Bone marrow Total eff. dose
Males
Females
Pd%
Mean (mSv)
Median (mSv)
Mean (mSv)
24.92 19.65 12.05 8.57 52.79 34.82 72.41 51.41 2.51 2.39 2.94 2.52 2.49 3.03 28.34 22.33 7.84 6.37 3.96 3.30 131.7 108.9 33.53 25.41 4.87 4.30
19.92 8.52 41.78 49.82 1.72 1.88 1.25 20.13 66.6 2.85 103.4 25.72 3.95
30.10 13.80 60.14 87.25 3.35 3.41 3.70 37.23 7.93 5.12 157.1 40.52 5.38
3.65 3.05 4.67 3.48 9.15 7.22
2.58 3.13 6.74
e 8.23 6.91 5.60 4.51
e 5.59 4.30
18.14 9.04 36.41 54.45 2.66 2.16 4.29 21.82 6.34 3.36 110.7 24.65 4.02
Median (mSv) 27.12 11.70 57.07 79.15 2.40 3.53 1.79 35.82 6.72 4.23 149.8 38.35 5.15
18.8 13.5 13.0 18.6 28.8 14.8 39.2 27.1 1.2 25.5 17.6 18.9 10.0
4.24 2.81 5.18 3.35 9.03 6.70
3.72 4.34 8.83
15.1 10.5 1.2
0.48 0.30 10.52 6.89 6.77 4.23
0.47 9.23 5.82
e 24.4 e
Comparison between male and female groups The mean and median calculated HT values for the organs receiving considerable amounts of radiation doses and E values in the female and male group using the MCNP5 and PCXMC2 codes are given in Tables 2 and 3, respectively. The median values were calculated in order to consider the distribution of the sample. The f2 tallies of MCNP5 code passed all the statistical and errors checks and the relative errors were less than 0.1%. The calculated relative errors were lower than 0.3% for the most irradiated organs and lower than 2% for the less irradiated organs. The corresponding value concerning the organs that were distal from the actual beam was less than 7%, because in that case the amount of photons reaching the organs was small. The average percentage deviations of all organs between the two groups were 17.2% and 16.5% using the MCNP5 and PCXMC2, respectively. The deviation between the mean and median value
was statistically significant, hence the distribution of the sample was not a normal distribution. Comparison between two Monte Carlo codes The calculated HT values for the organs receiving considerable amounts of radiation doses, in both female and male group using the MCNP5 and PCXMC2.0 Monte Carlo codes are presented through the histogram of Fig. 1. The Pd% of the values in Fig. 1 are presented in Table 4. Risk estimation The REID, that have arisen from the PCXMC2.0 dose results are given in Table 5 for the female and male group. The mean age was 60 years old for both groups. Discussion
Table 2 Calculated HT for female and male group using MCNP5 code. Organs/tissue
Females
Males
Mean (mSv) Liver Pancreas Adrenals Kidneys Stomach Lungs Spleen Ribs Small intestine Skin Lower spine Mid spine Colon large intestine Esophagus Muscle Upper large intestine Breasts Bone marrow Total eff. dose
29.77 12.54 61.24 91.30 2.87 3.14 3.25 32.72 7.24 5.16 139.45 33.59 4.94
17.93 8.24 37.11 56.89 2.33 2.00 3.89 22.61 5.84 3.37 112.63 24.36 3.70
Pd%
Median (mSv)
Mean (mSv)
Median (mSv)
26.89 10.49 56.24 82.88 2.05 3.22 1.63 37.75 6.17 4.24 149.8 37.46 4.73
24.76 19.54 10.98 7.81 52.71 34.42 75.56 53.59 2.14 2.09 2.74 2.38 2.14 2.72 24.83 23.27 7.23 5.88 3.99 3.32 117.25 110.53 27.97 25.23 4.53 4.00
19.63 7.88 42.16 51.54 1.46 1.77 1.05 21.19 5.16 2.88 105.38 25.74 3.71
18.4 13.3 15.0 18.9 29.3 13.5 41.1 27.4 0.1 25.5 17.3 18.3 8.7
3.76 2.51 6.03 3.87 8.33 6.21
3.28 5.06 8.14
3.26 2.75 5.43 4.03 8.54 6.74
2.33 3.65 6.36
14.2 10.5 2.5
0.44 0.27 4.64 2.99 5.88 3.66
0.45 4.26 5.19
e 3.82 3.06 4.92 3.94
e 2.91 3.81
e 19.4 e
Monte Carlo simulation was used in conjunction with DAP measurements to estimate the organ doses. Uncertainties during the estimation of HT apart from normal measurement errors are also related to patient displacements, variable patient anatomy, geometrical and substantial differences between the patients and the used mathematical phantoms for the derivation of the dose conversion coefficients. Larger deviations were found during the estimation of the HT in concerning the organs located outside the primary X-ray field or in the end of the beam. The organs receiving considerable amounts of radiation doses were the lumbar spine, the kidneys and the adrenals, for both genders. The respective HT values were 157.1 110.7 mSv, 87.25 54.45 mSv and 60.14 36.41 mSv, for the female group and 131.7 108.9 mSv, 72.41 51.41 mSv and 52.79 34.82 mSv for the male group using PCXMC2.0 code. These organs were located in the irradiated field of view for the majority of the projections. The large standard deviations of HT were due to the procedure’s complexity and the rarity. A significant difference is obvious in the values of HT (Tables 2 and 3) for female and male groups, for both codes. The percentage deviations varied between 1.2% and 39.2%, for PCXMC2.0 code, and between 0.1% and 41.1% for MCNP5 code.
E. Karavasilis et al. / Physica Medica 30 (2014) 432e436
435
Figure 1. Histogram of mean HT for the male and female group using MCNP5 and PCXMC2.0 codes.
The HT values were calculated for phantoms with standard dimensions. The actual patient thickness is a significant factor for the organ dose assessment, especially when the patient differs significantly from the standard patient phantom. It must be pointed out that while any changes in the phantom dimensions (height, mass) were allowed using the PCXMC2.0 code, the same process was quite difficult for the phantom of MCNP5 code in clinical routine. The DAP values in this study, were 4500 2600 cGycm2 and 5500 3300 cGycm2, in males and females, respectively. These values were comparable to the reported diagnostic reference levels, 5400 cGycm2 in biliary drainage and 5000 cGycm2 in biliary intervention [36]. In the NRPB-W14 the mean and the ranges of reported DAP values of 202 biliary drainage procedures were 3400 cGycm2, and 7100e9320 cGycm2, and in 182 biliary interventions were 4000 cGycm2 and 1900e10,000 cGycm2, respectively [37]. In our study the mean DAP values were in the range but
Table 4 Calculated Pd% between two codes per gender group. Organs/tissue
Females Pd%
Males Pd%
Liver Pancreas Adrenals Kidneys Stomach Lungs Spleen Ribs Small intestine Skin Lower spine Mid spine Colon large intestine Esophagus Muscle Upper large intestine Breasts Bone marrow
1.1 9.5 1.8 4.5 15.2 8.1 13.2 12.9 9.1 0.8 11.9 18.7 8.6 12.0 15.1 8.1 7.8 77.6
0.7 9.3 0.2 4.2 15.7 6.8 15.1 13.2 8.0 0.8 11.6 18.1 7.3 11.1 15.1 6.9 e 73.2
higher than the reported values of NRPB-W-14. The higher DAP values can be explained by the complexity of the procedure. The total radiographic and fluoroscopic times were 13.5 12.6 min and 13.9 9.5 min in males and females, respectively, comparable to the 13.35 min, which was the fluoroscopic time reported in NRPB-W14. The radiation exposure is related to deterministic and stochastic effects. The most critical deterministic effect, in interventional radiology, is temporary skin erythema or skin injury. The estimated threshold for radiation damage in skin is about 2 Gy. From Tables 2 and 3 deviating with the WT, we can calculate that the radiation exposure of the whole skin was about 5 mGy and 4 mGy using the both codes, for the female and male group, respectively. The most critical stochastic effect is cancer development that will result in death. The REID values that were presented in Table 5, were significant low. However, the higher values of REID are related with the possibility of lung cancer for women (0.000754%) and leukemia (0.000661% and 0.000664%), for the female and male group respectively, that was expected due to significant radiation burden of bone marrow. PCXMC2.0 don’t calculate the REID of breast cancer on males. The values of REID were lower than the corresponding values to other causes for mortality [38]. Cancer mortality for other reasons was 22.2% and 18.6%, as was calculated from PCXMC2.0 code, for males and females 60 years old, respectively. From Fig. 1 we can conclude that there was a rather good coincidence agreement between the results produced by the two Table 5 Calculated REID% per gender group for the induction of specific cancer types. Cancer type
Females REID
Males REID
Leukemia Breast cancer Colon cancer Liver cancer Lung cancer Stomach cancer Bladder cancer
0.000661% 7.75E6% 0.000197% 0.000109% 0.000754% 0.000104% 7.52E7%
0.000664% e 0.000278% 0.00013% 0.000317% 5.77E5% 6.00E7%
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Monte Carlo codes. The HT values for the organs receiving considerable amounts of radiation doses were varied, 0.16e73.2% for the male group and 1.10e77.6% for the female group. The major differences between the two code’s calculations were the HT values of the bone marrow. This is due to the difference in bone modeling between the two used phantoms and the subsequent different estimation of the bone marrow equivalent to doses for each of the two used codes. The results show that PCXMC2.0 software yields values larger than those produced by Monte Carlo method based on MCNP5 code. The accuracy and the reliability of the two codes have been proved. Both codes yield similar dose distributions over the body, as it is presented in Fig. 1. Conclusion Monte Carlo simulation (MCNP5 and PCXMC2.0 codes) was used in conjunction with DAP measurements in order to estimate both HT and E for patients undergoing PTBD examinations. The organs receiving the highest amounts of doses during these exams are lumbar spine, adrenals and kidneys for both genders. Moreover high values of REID are related to the possibility of lung cancer for women and leukemia for both women and men. Comparison of MCNP5 and PCXMC2.0 simulation results demonstrated that the percentage deviations were about to 10% in the most of organs. Taking into the account that PCXMC2.0 code’s simulation time was 60 min, ten times lower than the correspondence MCNP5, PCXMC2.0 can be used in clinical routine. However, further investigation is needed in order to decrease the radiation dose according to the ALARA principle. Medical staff should be aware of all technical parameters that might contribute to reduction of radiation exposure as far as the setting and review of reference dose values. Finally, quality control of the equipment will further optimize value of PTDB exams. References [1] Damilakis J, Koukourakis M, Hatjidakis A, Karabekios S, Gourtsoyiannis N. Radiation exposure to the hands of operators during angiographic procedures. Eur J Radiol 1995;21:72e5. ar T, Toklu T, Cag lan A, Onal E, Padovani R. Patient doses and [2] Bor D, Olg dosimetric evaluations in interventional cardiology. Phys Med 2009;25:31e 42. [3] Bozkurt A, Bor D. Simultaneous determination of equivalent dose to organs and tissues of the patient and of the physician in interventional radiology using Monte Carlo method. Phys Med Biol 2007;52:317e30. [4] Burcharth F, Nielbo N. Percutaneous transhepatic cholangiography with selective catheterization of the common bile duct. Am J Roentgenol 1976;127: 409e12. [5] Hart D, Hillier MC, Wall BF. Doses to patients from medical X-ray examinations in the UK. Review, NRPB-W14. Available at: http://www.hpa.org.uk/ webc/HPAwebFile/HPAweb_C/1194947421571; 2000. [6] Noto K, Matsubara K, Koshida K, Iida H, Yamamoto T. Evaluation of patient dosed due to fluoroscopic exposures. Radiat Prot Dosim 2011;146:234e6. [7] Laufer U, Kirchner J, Kickuth R, Adams S, Jendreck M, Liermann D. A comparative study of CT fluoroscopy combined with fluoroscopy versus fluoroscopy alone for percutaneous transhepatic biliary drainage. Cardiovasc Intervent Radiol 2001;24:240e4. [8] Le Heron JC. Estimation of effective dose to the patient during medical X-ray examinations from measurements of the dose-area product. Phys Med Biol 1992;37:2117e26. [9] Majewska N, Stanisi c MG, Klos MA, Makalowski M, Frankiewicz M, Juszkat R, et al. Patients’ radiation doses during thoracic stent-graft implantation: the problem of long-lasting procedures. Ann Thorac Surg 2012;93:465e72. [10] Neocleous A, Yakoumakis E, Gialousis G, Dimitriadis A, Yakoumakis N, Georgiou E. Dosimetry using Gafchromic XR-RV2 radiochromic films in interventional radiology. Radiat Prot Dosim 2011;147:78e82. [11] Olgar T, Bor D, Berkmen G, Yazar T. Patient and staff doses for some complex x-ray examinations. J Radiol Prot 2009;29:393e407.
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