The high dose and dose-per-pulse rates (up to 130 mGy/pulse) produced by some Intraoperative Radiation Therapy (IORT) accelerators pose specific dosimetric problems due to the high density of electric charge per pulse produced in the ionization chamber cavity. In particular, the correction factor for ion recombination, kscalculated with the two-voltage method is significantly overestimated and three alternative models have been proposed in the literature allowing for the presence of a free-electron component. However, at present there is no general consensus on the best model to assess the ion recombination correction and controversy remains on the uncertainty associated with ks. In the present work we adopted a Monte Carlo approach to assess the combined standard uncertainty associated with the ion recombination correction in plane-parallel chambers used in high dose-per-pulse electron beam dosimetry. The uncertainty associated with kswas calculated for the following plane-parallel ionization chambers: Scanditronix/Wellhofer Parallel Plate Chamber PPC05 and PPC40, PTW Advanced Markus Model N34045 and PTW Roos Model 34001. Input variables for MC calculations were derived from experimental data at 28 and 73 mGy/pulse. Taken together, the results of this study indicate that the three ion recombination models do not overlap within their standard uncertainties, indicating that an additional type-B uncertainty component would be necessary to take into account possible differences between the models. Our results indicate that the combined relative standard uncertainty in ksshould be calculated as the sum in quadrature of a (type-A) MC based uncertainty component and a (type-B) uncertainty contribution evaluated assuming a uniform distribution between ksvalues obtained from the two extreme models.

中文翻译：

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高剂量每脉冲电子束剂量学中与离子重组校正相关的不确定性评估：MC方法。

某些术中放射治疗（IORT）加速器产生的高剂量和每脉冲剂量率（最高130 mGy /脉冲）由于电离腔腔中产生的每个脉冲高电荷密度而引起特定的剂量学问题。特别是，用双电压方法计算的离子重组校正因子ks被大大高估了，文献中提出了三个可供选择的模型，这些模型允许存在自由电子组分。但是，目前尚无关于评估离子重组校正的最佳模型的普遍共识，而与ks相关的不确定性仍存在争议。在当前的工作中，我们采用了蒙特卡洛方法，以评估与高剂量每脉冲电子束剂量法中使用的平面平行腔室中的离子重组校正相关的组合标准不确定度。对于以下平面平行电离室，计算了与kswa相关的不确定性：Scanditronix / Wellhofer平行板室PPC05和PPC40，PTW Advanced Markus N34045型和PTW Roos 34001型。MC计算的输入变量来自28和73处的实验数据mGy /脉冲。两者合计，这项研究的结果表明，三个离子重组模型在它们的标准不确定度内不重叠，表明要考虑模型之间的可能差异，需要额外的B型不确定度成分。