Progress in Medical Physics (한국의학물리학회지:의학물리)

Korean Society of Medical Physics (한국의학물리학회)
권호 표지

Evaluation of Factors Used in AAPM TG-43 Formalism Using Segmented Sources Integration Method and Monte Carlo Simulation: Implementation of microSelectron HDR Ir-192 Source

미소선원 적분법과 몬테칼로 방법을 이용한 AAPM TG-43 선량계산 인자 평가: microSelectron HDR Ir-192 선원에 대한 적용

  • Ahn, Woo-Sang (Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine) ;
  • Jang, Won-Woo (Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine) ;
  • Park, Sung-Ho (Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine) ;
  • Jung, Sang-Hoon (Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine) ;
  • Cho, Woon-Kap (Radiation Research Department, Korea Institute of Nuclear Safety (KINS)) ;
  • Kim, Young-Seok (Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine) ;
  • Ahn, Seung-Do (Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine)
  • 안우상 (울산대학교 의과대학 서울아산병원 방사선종양학과) ;
  • 장원우 (울산대학교 의과대학 서울아산병원 방사선종양학과) ;
  • 박성호 (울산대학교 의과대학 서울아산병원 방사선종양학과) ;
  • 정상훈 (울산대학교 의과대학 서울아산병원 방사선종양학과) ;
  • 조운갑 (한국원자력안전기술원 방사선연구실) ;
  • 김영석 (울산대학교 의과대학 서울아산병원 방사선종양학과) ;
  • 안승도 (울산대학교 의과대학 서울아산병원 방사선종양학과)
  • Received : 2011.11.02
  • Accepted : 2011.12.05
  • Published : 2011.12.30
Download PDF
⟨ Previous Next ⟩

Abstract

Currently, the dose distribution calculation used by commercial treatment planning systems (TPSs) for high-dose rate (HDR) brachytherapy is derived from point and line source approximation method recommended by AAPM Task Group 43 (TG-43). However, the study of Monte Carlo (MC) simulation is required in order to assess the accuracy of dose calculation around three-dimensional Ir-192 source. In this study, geometry factor was calculated using segmented sources integration method by dividing microSelectron HDR Ir-192 source into smaller parts. The Monte Carlo code (MCNPX 2.5.0) was used to calculate the dose rate $\dot{D}(r,\theta)$ at a point ($r,\theta$) away from a HDR Ir-192 source in spherical water phantom with 30 cm diameter. Finally, anisotropy function and radial dose function were calculated from obtained results. The obtained geometry factor was compared with that calculated from line source approximation. Similarly, obtained anisotropy function and radial dose function were compared with those derived from MCPT results by Williamson. The geometry factor calculated from segmented sources integration method and line source approximation was within 0.2% for $r{\geq}0.5$ cm and 1.33% for r=0.1 cm, respectively. The relative-root mean square error (R-RMSE) of anisotropy function obtained by this study and Williamson was 2.33% for r=0.25 cm and within 1% for r>0.5 cm, respectively. The R-RMSE of radial dose function was 0.46% at radial distance from 0.1 to 14.0 cm. The geometry factor acquired from segmented sources integration method and line source approximation was in good agreement for $r{\geq}0.1$ cm. However, application of segmented sources integration method seems to be valid, since this method using three-dimensional Ir-192 source provides more realistic geometry factor. The anisotropy function and radial dose function estimated from MCNPX in this study and MCPT by Williamson are in good agreement within uncertainty of Monte Carlo codes except at radial distance of r=0.25 cm. It is expected that Monte Carlo code used in this study could be applied to other sources utilized for brachytherapy.

고선량률 근접치료에 사용되는 상업용 선원과 치료계획 시스템들은 AAPM TG 43에서 권고하는 점 및 선 선원에 의해 선량분포를 계산한다. 하지만, 근접치료용 선원에 대한 인체 내의 정확한 선량계산을 위해서 3차원 부피의 선원을 고려하는 MC 기반의 선량계산 방법이 필요하다. 본 연구에서는 microSelectron HDR Ir-192 선원을 작은 부분으로 분할하여 계산하는 미소선원 적분법을 이용하여 기하학적 인수를 계산하였다. 또한, 범용 방사선 수송코드인 MCNPX를 사용하여 30 cm 직경의 구형 물 팬텀 내에서 선원의 선량률을 계산하여 비등방성함수와 반경선량함수를 구하였다. 그 결과를 MC 기반 광자 수송코드인 MCPT를 사용하여 계산한 Williamson의 결과와 비교 및 분석하였다. 미소선원 적분법과 선 선원 근사법에 따른 기하학적 인수는 $r{\geq}0.5cm$에서는 0.2% 이내에서 일치하였고 r=0.1 cm일 때 1.33%의 차이를 보였다. 본 연구에서 계산된 비등방성함수와 반경선량함수가 Williamson의 계산된 결과의 차이는 비등방성함수의 경우 r=0.25 cm에 서 2.33%의 가장 큰 R-RMSE를 보였고 $r{\geq}0.5cm$에서는 1% 미만의 R-RMSE를 보였다. 반경선량함수의 경우는 r=0.1~14.0 cm에서 0.46%의 R-RMSE를 보였다. 미소선원 적분법과 선 선원 근사법으로 계산한 기하학적 인수는 $r{\geq}0.1cm$에서 잘 일치하지만 3차원의 Ir-192 선원을 적용하여 계산한 미소선원 적분법이 실제 기하학적 인수를 잘 반영할 것으로 생각된다. r=0.25 cm에서 비등방성함수를 제외하고는 MCPT와 MCNPX의 몬테칼로 코드를 이용하여 얻어진 비등방성함수와 반경선량함수는 각각의 몬테칼로 코드에 대한 불확실성 이내에서 잘 일치함을 확인하였다. 따라서 MCNPX 전산모사 결과를 통해 TG-43의 선량 계산식에 사용된 인자를 Williamson 등의 결과와 비교 및 검증함으로써, 추후 다른 종류의 선원에 대해서도 Monte Carlo 기반의 연구가 가능할 것으로 기대된다.

Keywords

References

  1. 지영훈, 김미숙, 류성렬, 유대헌, 최문식, 정해조: 방사선종양학 과 전국 통계(2006년). 방사선종양학회지 26(2):131-133 (2008)
  2. AAPM TG-56: Code of Practice for Brachytherapy Physics. Med Phys 24(10):1557-1598 (1997) https://doi.org/10.1118/1.597966
  3. AAPM TG-59: High Dose-rate Brachytherapy Treatment Delivery. Med Phys 25(4):375-403 (1998) https://doi.org/10.1118/1.598232
  4. 식품의약품안전청연구보고서 8-1: 근접방사선치료기 및 선원 에 대한 성능평가 기준 개발. 식품의약품안전청, 서울 (2004)
  5. AAPM TG-43: Dosimetry of Interstitial Brachytherapy Sources. Med Phys 22(2):209-234 (1995) https://doi.org/10.1118/1.597458
  6. Update of AAPM TG-43: Update of AAPM Task Group No.43 Report: A revised AAPM protocol for brachytherapy dose calcuations. Med Phys 31(3):633-674 (2004) https://doi.org/10.1118/1.1646040
  7. Supplement to AAPM TG-43 update: Supplement to the 2004 update of the AAPM Task Group No.43 Report. Med Phys 34(6):2187-2205 (2007) https://doi.org/10.1118/1.2736790
  8. Williamson J, Li Z: Monte Carlo aided dosimetry of the microselectron pulsed and high dose rate Ir-192 sources. Med Phys 22(6):809-819 (1995) https://doi.org/10.1118/1.597483
  9. Karaiskos P, Sakelliou L, Sandilos P, et al: Limitations of the point and line source approximations for the determination of geometry factors around brachytherapy souces. Med Phys 27(1):124-128 (2000) https://doi.org/10.1118/1.598873
  10. Denise B. Pelowitz: MCNPX user's manual version 2.5.0. LA-CP-05-0369 (Los Alamos, NM: Los Alamos National Laboratory) (2005)
  11. Brog J, Rogers DWO: Monte Carlo Calculations of Photon Spectra in Air From $^{192}Ir$ Sources. NRC-report PIRS 629r, Ottawa, Canada (1999)
  12. Rivard MJ, Granero D, Perez-Calatayud J, Ballester F: Influence of photon energy spectrum from brachytherapy sources on Monte Carlo simulations of kerma and dose rates in water and air. Med Phys 37(2):869-876 (2010) https://doi.org/10.1118/1.3298008
  13. Daskalov GM, Loffler E, Wlliamson JF: Monte Carlo-aided dosimetry of a new high dose-rate brachytherapy source. Med Phys 25(11):2200-2208 (1998) https://doi.org/10.1118/1.598418
  14. AAPM TG-138 and GEC-ESTRO: A dosimetric uncertainty analysis for photon-emitting brachytherapy sources. Med Phys 38(2):782-801 (2011) https://doi.org/10.1118/1.3533720
  15. Glasgow GP, Dillman LT: Specific gamma-ray constant and exposure rate constant for $^{192}Ir$. Med Phys 6(1):49-52 (1979)
  16. Roussin RW, Knight JR, Hubbell JH, Howerton RJ: Description of the DCL-99/Hugo Package of Photon Interactions. Oak Ridge National Laboratory, RSIC Data Library Collection, (Radiation Shielding Information Center, Report No. ORNL/ RSIC-46, Oak Ridge, TN) (1983)
  17. Tod M, Merecith WJ: Treatment of cancer of the cervix uteri- a revised "Manchester Method". Br J Radiol 26:252-257 (1953)
  18. Pierquin B, Wilson JF, Chassagne D: Modern Brachytherapy. New York, Masson (1987)