Medical Physics and Radiation Protection Service, Fuenlabrada University Hospital, Camino del Molino, 2, Fuenlabrada, Madrid, 28942, Spain.
Medical Physics and Radiation Protection Service, 12 de Octubre University Hospital, Av Cordoba, s/n, Madrid, 28041, Spain.
Med Phys. 2019 Apr;46(4):1896-1904. doi: 10.1002/mp.13424. Epub 2019 Feb 28.
The aim of this work is to develop a sensitometry model of EBT2 and EBT3 radiochromic films based on the observation that radiation induces growth of two polymer color phases.
Previously published data of the active layer absorption spectrum have been used to characterize the contribution to the total absorbance of each polymer color phase. Through a prior proposed external beam therapy absorption spectrum model the total absorbance has been deconvolved into two polymer phase contributions. The integral absorbance in the visible spectrum of each color phase has been calculated and parametrized as an absorbed dose function. A sensitometry model employing linear relationships with the color phase integral absorbances has been investigated. The phase linear coefficient ratio for each color channel is proposed to be a constant. Films belonging to six different production batches, three EBT2 and three EBT3, have been used to verify this model.
Each polymer color phase integral absorbance in the visible spectrum has been expressed as a simple saturation function of the absorbed dose to the film. The data coming from the six production batches have been fitted to the proposed sensitometry model. This model predicts the measured dose variation in the active layer light attenuation up to fluctuations attributable to uncertainties.
The calibration curve can be written as a linear combination of simple functions describing the dose dependence of the integral absorbance of each polymer color phase. These functions are characteristics of the active layer material, and not dependent on the model and production batch. According to the proposed model, to calibrate a batch in terms of the active layer light attenuation consists of determining just one linear coefficient.
本工作的目的是基于观察到辐射诱导两种聚合物颜色相生长的现象，开发 EBT2 和 EBT3 光致变色胶片的感光测定模型。
先前发表的活性层吸收光谱数据已被用于表征各聚合物颜色相的总吸收贡献。通过先前提出的外束治疗吸收光谱模型，总吸收已被分解为两个聚合物相贡献。已计算并参数化为吸收剂量函数的每个颜色相在可见光谱中的积分吸收。研究了采用与颜色相积分吸收线性关系的感光测定模型。建议每个颜色通道的相线性系数比为常数。使用属于六个不同生产批次的三个 EBT2 和三个 EBT3 的胶片验证了该模型。
已将可见光谱中每个聚合物颜色相的积分吸收表示为对胶片吸收剂量的简单饱和函数。来自六个生产批次的数据已拟合到所提出的感光测定模型。该模型预测了活性层光衰减中测量的剂量变化，直至波动归因于不确定性。
校准曲线可以写成描述各聚合物颜色相积分吸收对剂量依赖性的简单函数的线性组合。这些函数是活性层材料的特性，不依赖于模型和生产批次。根据所提出的模型，要根据活性层光衰减来校准一批胶片，只需确定一个线性系数。
