The alanine pellet dosimeter is a widely used reference dosimeter in both medical and industrial dosimetry across a wide range of beam qualities. A challenge when using alanine in low energy X-ray beams is its strong energy dependence; a significant decline is observed in the alanine response per dose-to-water relative to irradiations in a cobalt-60 reference field. This decrease is caused by the physical difference in alanine to water dose ratios combined with a radiochemical decrease in the intrinsic detector efficiency but is difficult to characterize mainly due to experimental uncertainties.

Here we have applied a microdosimetric one-hit detector model to characterize the intrinsic detector efficiency of the alanine pellet dosimeter in low energy X-ray beams. Microdosimetric distributions were estimated from track structure calculations using the Geant4-DNA Monte Carlo software, where literature data was used to determine free model parameters.

The model was applied to two sets of X-ray spectra with low (40 kV to 170 kV) and medium (100 kV to 300 kV) tube potential, covering a wide range of beam qualities. A relative detector efficiency of 0.937 was obtained for the low energy set with variations between −1.0% and 1.5%, whereas the efficiency varied between approximately 0.925 and 0.985 for the medium energy set, with a strong correlation to the half-value layer of the beam.

It is concluded, that the half-value layer of an X-ray beam is not sufficient characterization to uniquely determine the relative efficiency of an alanine pellet dosimeter. However, the variation in relative efficiency with respect to the half-value layer is small.

丙氨酸颗粒剂量计是医疗和工业剂量测定中广泛使用的参考剂量计，具有广泛的光束质量。在低能 X 射线束中使用丙氨酸时的一个挑战是它对能量的强烈依赖性。观察到相对于钴 60 参考场中的辐照，每剂量对水的丙氨酸反应显着下降。这种降低是由丙氨酸与水剂量比的物理差异以及本征检测器效率的放射化学降低引起的，但主要由于实验不确定性而难以表征。

在这里，我们应用了微剂量一击式探测器模型来表征丙氨酸颗粒剂量计在低能 X 射线束中的固有探测器效率。使用 Geant4-DNA Monte Carlo 软件从轨道结构计算中估计微剂量分布，其中文献数据用于确定自由模型参数。

该模型应用于具有低（40 kV 至 170 kV）和中（100 kV 至 300 kV）管电位的两组 X 射线光谱，涵盖了广泛的光束质量。低能量组的相对检测器效率为 0.937，变化在 -1.0% 和 1.5% 之间，而中等能量组的效率在大约 0.925 和 0.985 之间变化，与半值层有很强的相关性。光束。

得出的结论是，X 射线束的半值层不足以唯一确定丙氨酸颗粒剂量计的相对效率。然而，相对于半值层的相对效率的变化很小。