Rasouli Fatemeh S, Masoudi S Farhad
a Department of Physics , K.N. Toosi University of Technology , Tehran , Iran.
Int J Radiat Biol. 2017 Mar;93(3):351-356. doi: 10.1080/09553002.2017.1239136. Epub 2016 Oct 25.
Pre-clinical tests and simulation studies for radiotherapy are generally carried out using water or simplified materials. Investigating the effects of defining compositionally realistic media in proton transport studies was the objective of this work. Accurate modeling of the Bragg curve is a fundamental requirement for such a study.
An equation previously validated by experiments provides an appropriate analytical method for proton dose calculation in depth of the target. Owing to the dependency on protons ranges and the probability of undergoing non-elastic nuclear interactions (NNI), this formula comprises three parameters with values specified for initial proton energy and for the target material. As a result, knowledge of the depth-dose distribution using this analytical model is limited to the materials for which the data has been provided in nuclear data tables. In this study, we used our general formulas for calculating the protons ranges and the probability of undergoing NNI in desired compounds and mixtures with an arbitrary number of constituent elements. Furthermore, the protons dose distribution in the depth of these targets was leading off with determining the parameters appeared in the employed model using our mathematically easy to handle relations. For a number of tissues which may be of interest in proton radiotherapy studies but are missing in reference data tables, the mentioned parameters were calculated. Moreover, the resultant values for the protons ranges and the probability of undergoing NNIs were compared with those in water.
The results showed that the differences between the position of Bragg peaks in water and realistic media considered in this study were energy dependent, and ranged between a few millimeters. For proton beams of arbitrary chosen initial energies, the maximum dose delivered to the realistic media varied between about -0.02-4.42% in comparison with that to water.
The effects observed (both in penetration and in the magnitude of the Bragg peaks) may be overshadowed by the different dose prescriptions depending on the quality of the treatment planning system, and dosimetry protocols used at the various therapy centers.
放射治疗的临床前测试和模拟研究通常使用水或简化材料进行。本研究的目的是探讨在质子传输研究中定义成分逼真的介质的影响。对布拉格曲线进行精确建模是此类研究的基本要求。
一个先前经实验验证的方程为靶区深度的质子剂量计算提供了一种合适的分析方法。由于依赖于质子射程和发生非弹性核相互作用（NNI）的概率，该公式包含三个参数，其值针对初始质子能量和靶材料指定。因此，使用此分析模型对深度剂量分布的了解仅限于核数据表中已提供数据的材料。在本研究中，我们使用通用公式来计算所需化合物和具有任意数量组成元素的混合物中的质子射程和发生NNI的概率。此外，通过使用数学上易于处理的关系确定所用模型中出现的参数，得出这些靶区深度的质子剂量分布。对于质子放射治疗研究中可能感兴趣但参考数据表中缺少的一些组织，计算了上述参数。此外，将质子射程和发生NNIs的概率的结果值与水中的值进行了比较。
结果表明，本研究中考虑的水和逼真介质中布拉格峰位置的差异与能量有关，范围在几毫米之间。对于任意选择的初始能量的质子束与水相比，传递到逼真介质的最大剂量在约-0.02-4.42%之间变化。
根据治疗计划系统的质量以及各个治疗中心使用的剂量测定方案，不同的剂量处方可能会掩盖观察到的效应（包括穿透和布拉格峰的大小）。
