방사선의학 웹진

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Abstract
Background: Previous study proposed a method to measure linear energy transfer (LET) at specific points using the quenching magnitude of thin film solar cells. This study was conducted to propose a more advanced method for measuring the LET distribution.

Purpose: This study focuses on evaluating the feasibility of estimating the proton LET distribution in proton therapy. The feasibility of measuring the proton LET and dose distribution simultaneously using a single-channel configuration comprising two solar cells with distinct quenching constants is investigated with the objective of paving the way for enhanced proton therapy dosimetry.

Methods: Two solar cells with different quenching constants were used to estimate the proton LET distribution. Detector characteristics (e.g., dose linearity and dose-rate dependency) of the solar cells were evaluated to assess their suitability for dosimetry applications. First, using a reference beam condition, the quenching constants of the two solar cells were determined according to the modified Birks equation. The signal ratios of the two solar cells were then evaluated according to proton LET in relation to the estimated quenching constants. The proton LET distributions of six test beams were obtained by measuring the signal ratios of the two solar cells at each depth, and the ratios were evaluated by comparing them with those calculated by Monte Carlo simulation.

Results: The detector characterization of the two solar cells including dose linearity and dose-rate dependence affirmed their suitability for use in dosimetry applications. The maximum difference between the LET measured using the two solar cells and that calculated by Monte Carlo simulation was 2.34 keV/µm. In the case of the dose distribution measured using the method proposed in this study, the maximum difference between range measured using the proposed method and that measured using a multilayered ionization chamber was 0.7 mm. The expected accuracy of simultaneous LET and dose distribution measurement using the method proposed in this study were estimated to be 3.82%. The signal ratios of the two solar cells, which are related to quenching constants, demonstrated the feasibility of measuring LET and dose distribution simultaneously.

Conclusion: The feasibility of measuring proton LET and dose distribution simultaneously using two solar cells with different quenching constants was demonstrated. Although the method proposed in this study was evaluated using a single channel by varying the measuring depth, the results suggest that the proton LET and dose distribution can be simultaneously measured if the detector is configured in a multichannel form. We believe that the results presented in this study provide the envisioned transition to a multichannel configuration, with the promise of substantially advancing proton therapy's accuracy and efficacy in cancer treatment.

위 그림은 본 연구에서 고안한 박막 태양전지 기반 검출기의 단일채널을 이용하여 여러 깊이에서의 LET와 선량을 동시에 측정하여 기존의 검출기인 MLIC (Multi-layered ionization chamber)으로 측정한 Bragg peak와 몬테카를로로 계산한 양성자 LET 깊이와 비교한 결과입니다. 위 그림을 통해 박막 태양전지 기반의 검출기가 몬테카를로로 계산된 깊이에 따른 양성자 LET 분포와 기존의 Bragg peak를 측정할 수 있는 상용화된 장비인 MLIC으로 측정한 Bragg peak과 비교하였을 때 큰 차이 없이 양성자 LET와 방사선량 분포를 동시에 정확하게 측정할 수 있음을 보여줍니다.

Affiliations

Seonghoon Jeong 1, Chae-Eon Kim 2 3, Chankyu Kim 2, Sang-Il Pak 2, Seohyeon An 2 4, Wonjoong Cheon 5, Dongho Shin 2, Young Kyung Lim 2, Jong Hwi Jeong 2, Haksoo Kim 2, Yoonsun Chung 3, Sang Hyoun Choi 6, Se Byeong Lee 2
1Department of Neurosurgery, College of Medicine, Ilsan Paik Hospital, Inje University, Goyang, Republic of Korea.
2Proton Therapy Center, National Cancer Center, Goyang, Republic of Korea.
3Department of Nuclear Engineering, Hanyang University, Seoul, Republic of Korea.
4Department of Physics, Hanyang University, Seoul, Republic of Korea.
5Department of Radiation Oncology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea.
6Radiation Therapy Technology and Standards, Korea Institute of Radiological & Medical Sciences, Seoul, Republic of Korea.