Progress in Medical Physics (한국의학물리학회지:의학물리)

Korean Society of Medical Physics (한국의학물리학회)
권호 표지
DOI QR코드

DOI QR Code

The Comparative Analysis of External Dose Reconstruction in EPID and Internal Dose Measurement Using Monte Carlo Simulation

몬테 카를로 전산모사를 통한 EPID의 외부적 선량 재구성과 내부 선량 계측과의 비교 및 분석

  • Jung, Joo-Young (Department of Biomedical Engineering, Research Institute of Biomedical Engineering, School of Medicine, The Catholic University of Korea) ;
  • Yoon, Do-Kun (Department of Biomedical Engineering, Research Institute of Biomedical Engineering, School of Medicine, The Catholic University of Korea) ;
  • Suh, Tae-Suk (Department of Biomedical Engineering, Research Institute of Biomedical Engineering, School of Medicine, The Catholic University of Korea)
  • 정주영 (가톨릭대학교 의과대학 의공학교실, 가톨릭대학교 생체의공학연구소) ;
  • 윤도군 (가톨릭대학교 의과대학 의공학교실, 가톨릭대학교 생체의공학연구소) ;
  • 서태석 (가톨릭대학교 의과대학 의공학교실, 가톨릭대학교 생체의공학연구소)
  • Received : 2013.10.16
  • Accepted : 2013.12.05
  • Published : 2013.12.31
Download PDF
⟨ Previous Next ⟩

Abstract

The purpose of this study is to evaluate and analyze the relationship between the external radiation dose reconstruction which is transmitted from the patient who receives radiation treatment through electronic portal imaging device (EPID) and the internal dose derived from the Monte Carlo simulation. As a comparative analysis of the two cases, it is performed to provide a basic indicator for similar studies. The geometric information of the experiment and that of the radiation source were entered into Monte Carlo n-particle (MCNPX) which is the computer simulation tool and to derive the EPID images, a tally card in MCNPX was used for visualizing and the imaging of the dose information. We set to source to surface distance (SSD) 100 cm for internal measurement and EPID. And the water phantom was set to be 100 cm of the source to surface distance (SSD) for the internal measurement and EPID was set to 90 cm of SSD which is 10 cm below. The internal dose was collected from the water phantom by using mesh tally function in MCNPX, accumulated dose data was acquired by four-portal beam exposures. At the same time, after getting the dose which had been passed through water phantom, dose reconstruction was performed using back-projection method. In order to analyze about two cases, we compared the penetrated dose by calibration of itself with the absorbed one. We also evaluated the reconstructed dose using EPID and partially accumulated (overlapped) dose in water phantom by four-portal beam exposures. The sum dose data of two cases were calculated as each 3.4580 MeV/g (absorbed dose in water) and 3.4354 MeV/g (EPID reconstruction). The result of sum dose match from two cases shows good agreement with 0.6536% dose error.

본 연구의 목적은 electronic portal imaging device (EPID)를 통하여 방사선 치료를 받는 환자로부터 투과해 나오는 선량으로 외부적인 선량 재구성과 몬테카를로 전산모사로부터 도출되는 내부 선량 계측과의 관계를 도출하고 이를 분석하기 위한 연구로 진행되었다. 본 연구는 전산모사 연구로써 두 가지의 경우를 비교 분석하고 이와 비슷한 연구에 대한 기본적인 지표를 제공하고자 시행되었다. 실험에 관한 기하학적 정보와 방사선 소스에 대한 정보를 몬테카를로 전산모사 툴인 Monte Carlo n-particle (MCNPX)에 입력하였고 EPID 이미지 도출을 위하여 MCNPX 내에 tally카드를 이용하여 선량정보를 도출하고 이를 영상화 할 수 있도록 하였다. 또한 내부적인 계측을 위하여 물 팬텀을 소스와 표면의 거리(source to surface distance, SSD)가 100 cm이 되도록 설정하였으며, 그보다 10 cm 아래에 EPID를 위치시켰다. 내부 계측은 물팬텀 자체에서 흡수되는 흡수 선량을 mesh tally로 수집하였고, 4문 조사를 통하여 중첩된 선량에 대한 데이터를 획득하였다. 그와 동시에 EPID에서 물을 투과해 나오는 선량을 획득 한 뒤 역 투사 방법을 사용하여 선량 재구성을 하였다. 이둘의 경우를 비교하기 위해 자체적인 교정(calibration)을 통하여 투과해 나온 선량과 흡수된 선량과의 관계를 비교하고 4문 조사를 통하여 물 팬텀 내의 특정 부분에 대한 중첩된 선량 데이터와 EPID를 통해 재구성한 선량 데이터를 분석하였다. 물 팬텀과 EPID에서 획득한 누적 선량의 합은 각각 평균 3.4580 MeV/g과 3.4354 MeV/g이었다. 이는 앞서 계측된 물 팬텀 내부의 누적 선량과 0.6536% 선량 오차를 보였다.

Keywords

References

  1. Chang J, Obcemea CH, Sillanpaa J, Mechalakos J, Burman C: Use of EPID for leaf position accuracy QA of dynamic multi-leaf collimator (DMLC) treatment. Med Phys 31(7):2091-2096 (2004) https://doi.org/10.1118/1.1760187
  2. Parent L, Seco J, Evans PM, Dance DR, Fielding A: Evaluation of two methods of predicting MLC leaf positions using EPID measurements. Med Phys 33(9):3174-3182 (2006) https://doi.org/10.1118/1.2335490
  3. Vial P, Greer PB, Hunt P, Oliver L, Baldock C: The impact of MLC transmitted radiation on EPID dosimetry for dynamic MLC beams. Med Phys 35(4):1267-1277 (2008) https://doi.org/10.1118/1.2885368
  4. Greer PB, Cadman P, Lee C, Bzdusek K: An energy fluence-convolution model for amorphous silicon EPID dose prediction. Med Phys 36(2):547-555 (2009) https://doi.org/10.1118/1.3058481
  5. McDermott LN, Wendling M, van Asselen B, et al: Clinical experience with EPID dosimetry for prostate IMRT pretreatment dose verification. Med Phys 33(10):3921-3930 (2006) https://doi.org/10.1118/1.2230810
  6. Spezi E, Lewis DG: Full forward Monte Carlo calculation of portal dose from MLC collimated treatment beams. Phys MedBiol 47:377-390 (2002)
  7. Paganetti H, Jiang H, Lee SY, Kooy HM: Accurate Monte Carlo simulations for nozzle design, commissioning and quality assurance for a proton radiation therapy facility. Med Phys 31(7):2107-2118 (2004) https://doi.org/10.1118/1.1762792
  8. Newhauser W, Fontenot J, Zheng Y, et al: Monte Carlo simulations for configuring and testing an analytical proton dose-calculation algorithm. Phys Med Biol 52(15):4569-4584 (2007) https://doi.org/10.1088/0031-9155/52/15/014
  9. Titt U, Newhauser WD: Neutron shielding calculations in a proton therapy facility based on Monte Carlo simulations and analytical models: criterion for selecting the method of choice. Radiat Prot Dosim 115(1-4):144-148 (2005) https://doi.org/10.1093/rpd/nci252
  10. Titt U, Zheng Y, Vassiliev ON, Newhauser WD: Monte Carlo investigation of collimator scatter of proton-therapy beams produced using the passive scattering method. Phys Med Biol 53(2):487-504 (2008) https://doi.org/10.1088/0031-9155/53/2/014
  11. Baumgartner A, Steurer A, Maringer FJ: Simulation of photon energy spectra from Varian 2100C and 2300C/D Linacs: Simplified estimates with PENELOPE Monte Carlo models. Appl Radiat Isot 67(11):2007-2012 (2009) https://doi.org/10.1016/j.apradiso.2009.07.010
  12. Partridge M, Ebert M, Hesse BM: IMRT verification by three-dimensional dose reconstruction from portal beam measurements. Med Phys 29(8):1847-1858 (2002) https://doi.org/10.1118/1.1494988
  13. Wendling M, Louwe RJW, LN McDermott, Sonke JJ, van Herk M, Mijnheer BJ: Accurate two-dimensional IMRT verification using a back-projection EPID dosimetry method. Med Phys 33(2):259-273 (2006) https://doi.org/10.1118/1.2147744