이차원 양성자 선량 분포 확인을 위한 즉발감마선 이차원분포 측정 장치 개발

초록

In proton therapy, verification of proton dose distribution is important to treat cancer precisely and to enhance patients’ safety. To verify proton dose distribution, in a previous study, our team incorporated a vertically-aligned one-dimensional array detection system. We measured 2D prompt-gamma distribution moving the developed detection system in the longitudinal direction and verified similarity between 2D prompt-gamma distribution and 2D proton dose distribution. In the present, we have developed two-dimension prompt-gamma measurement system consisted of a 2D parallel-hole collimator, 2D array-type NaI(Tl) scintillators, and multi-anode PMT (MA-PMT) to measure 2D prompt-gamma distribution in real time. The developed measurement system was tested with 22Na (0.511 and 1.275 MeV) and 137Cs (0.662 MeV) gamma sources, and the energy resolutions of 0.511, 0.662 and 1.275 MeV were 10.9%±0.23p%, 9.8%±0.18p% and 6.4%±0.24p%, respectively. Further, the energy resolution of the high gamma energy (3.416 MeV) of double escape peak from Am-Be source was 11.4%±3.6p%. To estimate the performance of the developed measurement system, we measured 2D prompt-gamma distribution generated by PMMA phantom irradiated with 45 MeV proton beam of 0.5 nA. As a result of comparing a EBT film result, 2D prompt-gamma distribution measured for 9×109 protons is similar to 2D proton dose distribution. In addition, the 45 MeV estimated beam range by profile distribution of 2D prompt gamma distribution was 17.0±0.4 mm and was intimately related with the proton beam range of 17.4 mm.

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