Rijken James, Kairn Tanya, Crowe Scott, Muñoz Luis, Trapp Jamie
Genesis Care, Flinders Private Hospital, Bedford Park, SA, Australia.
Queensland University of Technology, Brisbane, QLD, Australia.
J Appl Clin Med Phys. 2018 Jul;19(4):239-245. doi: 10.1002/acm2.12394. Epub 2018 Jun 22.
The ability to accurately predict skin doses and thereby design radiotherapy treatments that balance the likelihood of skin reactions against other treatment objectives is especially important when hypofractionated prescription regimes are used. However, calculations of skin dose provided by many commercial radiotherapy treatment planning systems are known to be inaccurate, especially if the presence of immobilization equipment is not accurately taken into account. This study proposes a simple method by which the accuracy of skin dose calculations can be substantially improved, to allow informed evaluation of volumetric modulated arc therapy (VMAT) treatment plans.
A simple method was developed whereby dose calculation is split into grid regions, each with a correction factor which determines MU scaling for skin dose calculation. Correction factors were derived from film measurements made using a geometrically simple phantom in partial contact with a vacuum immobilization device. This method was applied to two different test treatments, planned for delivery to a humanoid phantom with a hypofractionated stereotactic body radiotherapy technique, and results were verified using film measurements of surface dose.
Compared to the measured values, calculations of skin dose volumes corresponding to different grade tissue reactions were greatly improved through use of the method employed in this study. In some cases, the accuracy of skin dose evaluation improved by 76% and brought values to within 3% of those measured.
The method of skin dose calculation in this study is simple, can be made as accurate as the user requires and is applicable for various immobilization systems. This concept has been verified through use on SBRT lung treatment plans and will aid clinicians in predicting skin response in patients.
当采用大分割处方方案时，准确预测皮肤剂量并据此设计能在皮肤反应可能性与其他治疗目标之间取得平衡的放射治疗方案的能力尤为重要。然而，许多商业放射治疗计划系统所提供的皮肤剂量计算已知是不准确的，尤其是在未准确考虑固定设备存在的情况下。本研究提出一种简单方法，通过该方法可大幅提高皮肤剂量计算的准确性，以便对容积调强弧形治疗（VMAT）治疗计划进行明智的评估。
开发了一种简单方法，即将剂量计算划分为网格区域，每个区域都有一个校正因子，该因子决定用于皮肤剂量计算的MU缩放。校正因子源自使用与真空固定装置部分接触的几何形状简单的体模进行的胶片测量。将此方法应用于两种不同的测试治疗，计划采用大分割立体定向体部放射治疗技术施用于人形体模，并使用表面剂量的胶片测量来验证结果。
与测量值相比，通过使用本研究中采用的方法，对应于不同等级组织反应的皮肤剂量体积计算有了很大改进。在某些情况下，皮肤剂量评估的准确性提高了76%，并使数值与测量值的偏差在3%以内。
本研究中的皮肤剂量计算方法简单，可根据用户需求达到所需的准确度，适用于各种固定系统。这一概念已通过在SBRT肺部治疗计划中的应用得到验证，将有助于临床医生预测患者的皮肤反应。
