Computational model for detector timing effects in Compton-camera based prompt-gamma imaging for proton radiotherapy.
Computational model for detector timing effects in Compton-camera based prompt-gamma imaging for proton radiotherapy.
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DOI：
10.1088/1361-6560/ab8bf0
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发表时间：
2020-06-18
影响因子：
3.5
通讯作者：
Polf J
中科院分区：
文献类型：
--
作者：
Maggi P;Peterson S;Panthi R;Mackin D;Yang H;He Z;Beddar S;Polf J
本文描述了基于康普顿相机(CC)的瞬发伽马(PG)成像系统的真实模拟，用于验证临床剂量率范围的质子射程，并与临床前CC的PG测量数据进行了比较。我们使用蒙特卡罗加探测器效应(MCDE)模型来模拟瞬发伽马射线(PG)的产生及其在CC中的能量沉积。用蒙特卡罗方法模拟了150 MeV质子铅笔束辐照高密度聚乙烯模体在5.0×108、2.6×109和4.6×109p+/S剂量率下的PG发射，并在后处理中加入了真实的探测器时序效应(如延迟触发时间、事件符合、死区时间等)以允许灵活的计数率变化。我们在临床用150 MeV质子铅笔束以相同的剂量率进行照射期间，获得了我们的临床前CC的PG发射测量。对于模拟和测量，随着剂量率的增加，PG发射数据可以看到三个主要变化：1)由于死区时间百分比的增加，检测到的事件总数减少；2)错误符合事件的增加(即多个PG相互作用，而不是单个PG散射)；以及3)能量谱中不同的PG发射峰的损失。我们使用MCDE模型来评估我们测量的PG数据的质量，主要是关于CC记录的真和假二次散射和三次散射。模拟结果表明，在5.0×108、2.6×109和4.6×109p+/S处，记录的二次散射PG相互作用中有22%、57%和70%是假二次散射；对于三次散射相互作用，分别有3%、21%和35%是假事件。这些虚假散射事件代表了数据中的噪声，而这些事件在数据中的高百分比代表了我们使用原型CC生成可用的PG图像的能力的主要限制。
This paper describes a realistic simulation of a Compton-camera (CC) based prompt-gamma (PG) imaging system for proton range verification for a range of clinical dose rates, and its comparison to PG measured data with a pre-clinical CC. We used a Monte Carlo plus Detector Effects (MCDE) model to simulate the production of prompt gamma-rays (PG) and their energy depositions in the CC. With Monte Carlo, we simulated PG emission resulting from irradiation of a high density polyethylene phantom with a 150 MeV proton pencil beam at dose rates of 5.0×108, 2.6×109, and 4.6×109 p+/s. Realistic detector timing effects (e.g. delayed triggering time, event-coincidence, dead time, etc,) were added in post-processing to allow for flexible count rate variations. We acquired PG emission measurements with our pre-clinical CC during irradiation with a clinical 150 MeV proton pencil beam at the same dose rates. For simulations and measurements, three primary changes could be seen in the PG emission data as the dose rate increased: 1) reduction in the total number of detected events due to increased dead-time percentage; 2) increase in false-coincidence events (i.e. multiple PGs interacting, rather than a single PG scatter); and 3) loss of distinct PG emission peaks in the energy spectrum. We used the MCDE model to estimate the quality of our measured PG data, primarily with regards to true and false double-scatters and triple-scatters recorded by the CC. The simulation results showed that of the recorded double-scatter PG interactions 22%, 57%, and 70% were false double-scatters and for triple-scatter interactions 3%, 21%, and 35% were false events at 5.0×108, 2.6×109, and 4.6×109 p+/s, respectively. These false scatter events represent noise in the data, and the high percentage of these events in the data represents a major limitation in our ability to produce usable PG images with our prototype CC.
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