대다수의 근접치료용 방사선치료계획장치는 AAPM TG-43의 계산식에 기반을 둔 선량계산 알고리듬을 적용하고 있으나 이는 조직의 비균질성을 적절히 고려하지 못한다. 본 연구에서는 몬테칼로 방법을 이용하여 강내고선량근접치료계획을 검증하는 체계를 구축하고자 하였으며, 특히 환자의 CT 영상을 이용하여 물질정보로 변환한 후 직접 몬테칼로 계산을 수행하는 방법의 타당성에 초점을 맞추었다. 판형 팬텀 및 자궁경부암 환자의 CT 영상을 Plato (Nucletron, Netherlands) 치료계획장치를 이용하여 근접치료계획을 수행한 후 여기서 얻어진 인자들을 이용하여 EGSnrc 기반의 DOSXYZnrc 코드로 몬테칼로 계산을 수행하였으며, EBT 필름측정 결과와 비교하였다. DOSXYZnrc 코드의 선원 모델링 특성 상 후장전 장치의 $^{192}Ir$ 선원들을 직육면체 형태로 근사화하여 모델링하였으며 계산 시 체적소의 크기는 $2{\times}2{\times}2\;mm^3$로 하였다. 균질 매질 내에서는 TG-43 기반의 선량계산 결과와 몬테칼로 선량계산 결과가 잘 일치함을 확인할 수 있었으나 고밀도 물질이 포함된 비균질 매질 내에서는 오차가 커졌다. 환자의 경우 A점 및 B점의 오차는 3% 이내, 평균선량 오차는 5% 정도였다. 그러나 기존 선량계산 알고리듬의 경우 고밀도 물질의 영향을 적절히 고려하지 못하여 표적의 선량을 과대평가하여 실제로는 더 적은 선량이 들어갈 우려가 있다. 본 연구에서 제안된 선량계산 검증체계는 타당하며 선량 계산 결과도 실제와 잘 일치함을 확인할 수 있었다. 또한 기존의 선량계산 알고리듬으로 계산된 치료계획결과를 확인할 경우에는 주의가 필요하며, 몬테칼로 방법과 같은 독립적인 검증 시스템이 유용할 것이다.
대다수의 근접치료용 방사선치료계획장치는 AAPM TG-43의 계산식에 기반을 둔 선량계산 알고리듬을 적용하고 있으나 이는 조직의 비균질성을 적절히 고려하지 못한다. 본 연구에서는 몬테칼로 방법을 이용하여 강내고선량근접치료계획을 검증하는 체계를 구축하고자 하였으며, 특히 환자의 CT 영상을 이용하여 물질정보로 변환한 후 직접 몬테칼로 계산을 수행하는 방법의 타당성에 초점을 맞추었다. 판형 팬텀 및 자궁경부암 환자의 CT 영상을 Plato (Nucletron, Netherlands) 치료계획장치를 이용하여 근접치료계획을 수행한 후 여기서 얻어진 인자들을 이용하여 EGSnrc 기반의 DOSXYZnrc 코드로 몬테칼로 계산을 수행하였으며, EBT 필름측정 결과와 비교하였다. DOSXYZnrc 코드의 선원 모델링 특성 상 후장전 장치의 $^{192}Ir$ 선원들을 직육면체 형태로 근사화하여 모델링하였으며 계산 시 체적소의 크기는 $2{\times}2{\times}2\;mm^3$로 하였다. 균질 매질 내에서는 TG-43 기반의 선량계산 결과와 몬테칼로 선량계산 결과가 잘 일치함을 확인할 수 있었으나 고밀도 물질이 포함된 비균질 매질 내에서는 오차가 커졌다. 환자의 경우 A점 및 B점의 오차는 3% 이내, 평균선량 오차는 5% 정도였다. 그러나 기존 선량계산 알고리듬의 경우 고밀도 물질의 영향을 적절히 고려하지 못하여 표적의 선량을 과대평가하여 실제로는 더 적은 선량이 들어갈 우려가 있다. 본 연구에서 제안된 선량계산 검증체계는 타당하며 선량 계산 결과도 실제와 잘 일치함을 확인할 수 있었다. 또한 기존의 선량계산 알고리듬으로 계산된 치료계획결과를 확인할 경우에는 주의가 필요하며, 몬테칼로 방법과 같은 독립적인 검증 시스템이 유용할 것이다.
Most brachytherapy treatment planning systems employ a dosimetry formalism based on the AAPM TG-43 report which does not appropriately consider tissue heterogeneity. In this study we aimed to set up a simple Monte Carlo-based intracavitary high-dose-rate brachytherapy (IC-HDRB) plan verification pla...
Most brachytherapy treatment planning systems employ a dosimetry formalism based on the AAPM TG-43 report which does not appropriately consider tissue heterogeneity. In this study we aimed to set up a simple Monte Carlo-based intracavitary high-dose-rate brachytherapy (IC-HDRB) plan verification platform, focusing particularly on the robustness of the direct Monte Carlo dose calculation using material and density information derived from CT images. CT images of slab phantoms and a uterine cervical cancer patient were used for brachytherapy plans based on the Plato (Nucletron, Netherlands) brachytherapy planning system. Monte Carlo simulations were implemented using the parameters from the Plato system and compared with the EBT film dosimetry and conventional dose computations. EGSnrc based DOSXYZnrc code was used for Monte Carlo simulations. Each $^{192}Ir$ source of the afterloader was approximately modeled as a parallel-piped shape inside the converted CT data set whose voxel size was $2{\times}2{\times}2\;mm^3$. Bracytherapy dose calculations based on the TG-43 showed good agreement with the Monte Carlo results in a homogeneous media whose density was close to water, but there were significant errors in high-density materials. For a patient case, A and B point dose differences were less than 3%, while the mean dose discrepancy was as much as 5%. Conventional dose computation methods might underdose the targets by not accounting for the effects of high-density materials. The proposed platform was shown to be feasible and to have good dose calculation accuracy. One should be careful when confirming the plan using a conventional brachytherapy dose computation method, and moreover, an independent dose verification system as developed in this study might be helpful.
Most brachytherapy treatment planning systems employ a dosimetry formalism based on the AAPM TG-43 report which does not appropriately consider tissue heterogeneity. In this study we aimed to set up a simple Monte Carlo-based intracavitary high-dose-rate brachytherapy (IC-HDRB) plan verification platform, focusing particularly on the robustness of the direct Monte Carlo dose calculation using material and density information derived from CT images. CT images of slab phantoms and a uterine cervical cancer patient were used for brachytherapy plans based on the Plato (Nucletron, Netherlands) brachytherapy planning system. Monte Carlo simulations were implemented using the parameters from the Plato system and compared with the EBT film dosimetry and conventional dose computations. EGSnrc based DOSXYZnrc code was used for Monte Carlo simulations. Each $^{192}Ir$ source of the afterloader was approximately modeled as a parallel-piped shape inside the converted CT data set whose voxel size was $2{\times}2{\times}2\;mm^3$. Bracytherapy dose calculations based on the TG-43 showed good agreement with the Monte Carlo results in a homogeneous media whose density was close to water, but there were significant errors in high-density materials. For a patient case, A and B point dose differences were less than 3%, while the mean dose discrepancy was as much as 5%. Conventional dose computation methods might underdose the targets by not accounting for the effects of high-density materials. The proposed platform was shown to be feasible and to have good dose calculation accuracy. One should be careful when confirming the plan using a conventional brachytherapy dose computation method, and moreover, an independent dose verification system as developed in this study might be helpful.
* AI 자동 식별 결과로 적합하지 않은 문장이 있을 수 있으니, 이용에 유의하시기 바랍니다.
제안 방법
Default 5 media in the PEGS4 data were used to simulate a patient plan (AIR521ICRU, LUNG521ICRU, ICRUTISSUE521ICRU, ICRPBONE521ICRU, STEEL521ICRU), while PMMA521ICRU was used for a phantom simulation. 3DDOSE data from the simulation of each single source were integrated with their own weights using the in-house program, which was developed using MATLAB 2009a (Mathworks, USA), and the data were then converted to the Pinnacle3 dose format. Exported dose data from the Plato were converted to the Pinnacle3 dose format for an evaluation.
The Pinnacle3 format CT data was converted into EGSPHANT format data by the CTCREATE code, and the source positions and weights from the plan data were used for a Monte Carlo simulation as well. Default 5 media in the PEGS4 data were used to simulate a patient plan (AIR521ICRU, LUNG521ICRU, ICRUTISSUE521ICRU, ICRPBONE521ICRU, STEEL521ICRU), while PMMA521ICRU was used for a phantom simulation. 3DDOSE data from the simulation of each single source were integrated with their own weights using the in-house program, which was developed using MATLAB 2009a (Mathworks, USA), and the data were then converted to the Pinnacle3 dose format.
Once a phantom or a patient was CT-scanned, the image set was sent to both the Plato and the Pinnacle3 . Following IC-HDRB planning with the Plato, the plan data, including doses, source positions, and weights were exported for a Monte Carlo simulation and a dose evaluation. The Pinnacle3 format CT data was converted into EGSPHANT format data by the CTCREATE code, and the source positions and weights from the plan data were used for a Monte Carlo simulation as well.
In this study, we did not model the applicator exactly, but instead used CT data directly by converting to a specific material and density matrix. Although the metal applicator and shielding material may cause serious artifacts on CT images; the artifact can be properly handled if a well-tuned CT number-material/density curve is used in converting the procedure to EGSPHANT format.
However, patient-specific Monte Carlo modeling based on CT images using general purpose Monte Carlo code has not been investigated sufficiently. In this study, we set up a simple Monte Carlo-based IC-HDRB plan verification system, with a particular focus on the robustness of the direct Monte Carlo dose calculation using material and density information derived from CT images.
It was not also necessary in this study to use exact modeling of the source because, from a macroscopic point of view, the source dimension is smaller than the voxel size and the superposition of the dose distributions of a single source reduces the overall uncertainty in the simplified source model. Thus we can say that the system described here would be feasible for clinical purposes.
Following IC-HDRB planning with the Plato, the plan data, including doses, source positions, and weights were exported for a Monte Carlo simulation and a dose evaluation. The Pinnacle3 format CT data was converted into EGSPHANT format data by the CTCREATE code, and the source positions and weights from the plan data were used for a Monte Carlo simulation as well. Default 5 media in the PEGS4 data were used to simulate a patient plan (AIR521ICRU, LUNG521ICRU, ICRUTISSUE521ICRU, ICRPBONE521ICRU, STEEL521ICRU), while PMMA521ICRU was used for a phantom simulation.
대상 데이터
The phantom was CT-scanned using a Brilliance Big Bore CT simulator (Philips Medical Systems, Netherlands), followed by the procedure described in previous section. A straight catheter model 084400 (Nucletron, Netherlands) was inserted into the center of the phantom. Because the catheter was made of stainless steel, it might create artifacts on the CT images.
The microSelectron-HDR 192Ir afterloader (Nucletron, Netherlands) and catheters were used for a treatment. The 192Ir source of the afterloader was modeled as a 3.
2. The microSelectron-HDR 192Ir afterloader and the PMMA slab phantom used in this study.
후속연구
Conventional dose computation methods might underdose the targets by not accounting for the effects of high-density materials. Therefore, when making a plan using a conventional brachytherapy dose computation method, one should be careful when confirming the plan, and moreover, an independent dose verification system as developed in this study might be helpful.
참고문헌 (18)
Angelopoulos A, Baras P, Sakelliou L, Karaiskos P, Sandilos P: Monte carlo dosimetry of a new 192Ir high dose rate brachytherapy source. Med Phys 27:2521-2527 (2000)
Karaiskos P, Angelopoulos A, Sakelliou L, et al: Monte carlo and TLD dosimetry of an 192Ir high dose-rate brachytherapy source. Med Phys 25:1975-1984 (1998)
Meigooni AS, Kleiman MT, Johnson JL, Mazloomdoost D, Ibbott GS: Dosimetric characteristics of a new high-intensity 192Ir source for remote afterloading. Med Phys 24:2008-2013 (1997)
Melhus CS, Rivard MJ: Approaches to calculating AAPM TG-43 brachytherapy dosimetry parameters for 137Cs, 125I, 192Ir, 103Pd, and 169Yb sources. Med Phys 33:1729-1737 (2006)
Rivard MJ, Coursey BM, DeWerd LA, et al: Update of AAPM task group no. 43 report: A revised AAPM protocol for brachytherapy dose calculations. Med Phys 31:633-674 (2004)
Nath R, Anderson LL, Luxton G, Weaver KA, Williamson JF, Meigooni AS: Dosimetry of interstitial brachytherapy sources: Recommendations of the AAPM radiation therapy committee task group no. 43. american association of physicists in medicine. Med Phys 22:209-234 (1995)
Anagnostopoulos G, Baltas D, Karaiskos P, Pantelis E, Papagiannis P, Sakelliou L: An analytical dosimetry model as a step towards accounting for inhomogeneities and bounded geometries in 192Ir brachytherapy treatment planning. Phys Med Biol 48:1625-1647 (2003)
Tedgren AK, Ahnesjo A: Accounting for high Z shields in brachytherapy using collapsed cone superposition for scatter dose calculation. Med Phys 30:2206-2217 (2003)
ICRU Report 38: Dose and volume specifications for reporting intracavitary therapy in gynecology. International Commission on Radiation Units and Measurements, Bethesda, MD (1985)
Shin KH, Kim TH, Cho JK, et al: CT-guided intracavitary radiotherapy for cervical cancer: Comparison of conventional point A plan with clinical target volume-based three-dimensional plan using dose-volume parameters. Int J Radiat Oncol Biol Phys 64:197-204 (2006)
Poon E, Williamson JF, Vuong T, Verhaegen F: Patientspecific monte carlo dose calculations for high-dose-rate endorectal brachytherapy with shielded intracavitary applicator. Int J Radiat Oncol Biol Phys 72:1259-1266 (2008)
Taylor RE, Yegin G, Rogers DW: Benchmarking brachydose: Voxel based EGSnrc monte carlo calculations of TG-43 dosimetry parameters. Med Phys 34:445-457 (2007)
※ AI-Helper는 부적절한 답변을 할 수 있습니다.