Monte Carlo calculations for absolute dosimetry to determine machine outputs for proton therapy fields
Monte Carlo calculations for absolute dosimetry to determine machine outputs for proton therapy fields
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DOI：
10.1088/0031-9155/51/11/008
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发表时间：
2006-06-07
影响因子：
3.5
通讯作者：
Paganetti, Harald
中科院分区：
文献类型：
--
作者：
Paganetti, Harald
放射治疗中的处方剂量必须转换为机器监测单位，以供患者治疗。对于每个扩展布拉格峰（SOBP）场，通过校准测量、通过使用分析算法或通过依赖于经验数据来常规地完成这一点。在东北质子治疗中心，监测单元对应于治疗头内分段传输电离室中收集的固定电荷量。这项工作的目标是使用治疗头的详细蒙特卡罗模型来计算作为电离室阅读的函数输送给患者的剂量，即以机器监视器单位计算患者的绝对剂量。结果表明，与测量结果非常一致。对于本研究中考虑的50个SOBP场，实验值和计算值之间的平均绝对差为1.5%，其中相似的50%的场在1%以内。这在数据的不确定性范围内。蒙特卡罗方法比分析算法具有优势，因为它考虑了散射和二次辐射，不依赖于经验参数，并提供了一种工具来研究治疗头的部件对电离室阅读的影响。与实验方法相比，蒙特卡罗方法具有能够验证患者几何形状中的剂量的优点。
The prescribed dose in radiation therapy has to be converted into machine monitor units for patient treatment. This is done routinely for each spread-out Bragg peak (SOBP) field either by calibration measurements, by using analytical algorithms or by relying on empirical data. At the Northeast Proton Therapy Center, a monitor unit corresponds to a fixed amount of charge collected in a segmented transmission ionization chamber inside the treatment head. The goal of this work was to use a detailed Monte Carlo model of the treatment head to calculate the dose delivered to the patient as a function of ionization chamber reading, i.e. to yield absolute dose in patients in terms of machine monitor units. The results show excellent agreement with measurements. For 50 SOBP fields considered in this study, the mean absolute difference between the experimental and the calculated value is 1.5%, where similar to 50% of the fields agree within 1%. This is within the uncertainties of the data. The Monte Carlo method has advantages over analytical algorithms because it takes into account scattered and secondary radiation, does not rely on empirical parameters, and provides a tool to study the influence of parts of the treatment head on the ionization chamber reading. Compared to experimental methods the Monte Carlo method has the advantage of being able to verify the dose in the patient geometry.