Department of Medical Physics, Shanghai Proton and Heavy Ion Center, Shanghai, China.
Shanghai Key Laboratory of Radiation Oncology(20dz2261000), Shanghai, China.
J Appl Clin Med Phys. 2022 Jul;23(7):e13636. doi: 10.1002/acm2.13636. Epub 2022 May 20.
To investigate the dose-sensitometric response of extended dose range (EDR2) films to scanning carbon-ion beams and to evaluate the applications of the obtained response curves to carbon-ion dose distributions.
EDR2 films were irradiated by mono-energetic scanning carbon-ion beams with different doses to obtain sensitometric curves at different integrated depth doses (DDDs). Six different DDDs were generated by using a proper buildup for each mono-energetic beam and were used to investigate the energy dependence. The sensitometric curves were obtained by fitting the net optical density (netOD) to dose at different DDDs. The dose difference between the value converted from the netOD and that calculated in the treatment planning system (TPS) was investigated to evaluate the application scope of the sensitometric curve.
Digitizing the EDR2 film with a resolution of 0.36 (72 dpi) provided a good signal-to-noise ratio, and the sensitometric curve was linear at all DDDs of clinically relevant incident kinetic energies in the netOD range of 0.02-1.70 for carbon-ion film dosimetry. The factors used to convert the netOD to absorbed dose were expressed as a linear function of DDDs, with which the depth dose difference between converted and TPS was less than 3% in the proximal area for incident kinetic energies lower than 307.5 MeV/u.
The EDR2 film is a feasible tool for scanning carbon-ion beam profile measurements by directly evaluating the netOD distribution with proper digitizing resolution and netOD range. By applying the conversion factors, the EDR2 film can also be employed to perform the percentage depth dose consistency checking and linear energy transfer comparison of carbon-ion lower than 307.5 MeV/u.
研究扩展剂量范围（EDR2）胶片对扫描碳离子束的剂量-感光响应，并评估获得的响应曲线在碳离子剂量分布中的应用。
用不同剂量的单能扫描碳离子束照射 EDR2 胶片，在不同的积分深度剂量（DDD）下获得感光曲线。对于每一种单能束，使用适当的堆积层来生成 6 个不同的 DDD，以研究能量依赖性。通过拟合不同 DDD 下的净光密度（netOD）与剂量，得到感光曲线。通过研究从 netOD 转换的值与治疗计划系统（TPS）中计算的值之间的剂量差异，评估感光曲线的应用范围。
以 0.36（72dpi）的分辨率数字化 EDR2 胶片，可获得良好的信噪比，在 netOD 范围为 0.02-1.70 的临床相关入射动能的所有 DDD 下，感光曲线均呈线性。用于将 netOD 转换为吸收剂量的因子表示为 DDD 的线性函数，对于入射动能低于 307.5MeV/u 的情况，转换后和 TPS 之间的深度剂量差异在近端区域小于 3%。
EDR2 胶片是一种可行的工具，可通过直接评估适当数字化分辨率和 netOD 范围内的净光密度分布来测量扫描碳离子束的束流剖面。通过应用转换因子，EDR2 胶片还可以用于进行低于 307.5MeV/u 的碳离子百分深度剂量一致性检查和线性能量传递比较。
