Jurado-Bruggeman Diego, Muñoz-Montplet Carles
Medical Physics and Radiation Protection Department, Catalan Institute of Oncology Girona, Girona, Spain.
Department of Medical Sciences, University of Girona, Girona, Spain.
Phys Imaging Radiat Oncol. 2023 Apr 28;26:100443. doi: 10.1016/j.phro.2023.100443. eCollection 2023 Apr.
Radiotherapy planning considerations were developed for the previous calculation algorithms yielding dose to water-in-water (). Advanced algorithms improve accuracy, but their dose values in terms of dose to medium-in-medium () depend on the medium considered. This work aimed to show how mimicking planning with can introduce new issues.
A head and neck case involving bone and metal heterogeneities outside the CTV was considered. Two different commercial algorithms were used to obtain and distributions. First, a plan was optimised to irradiate the PTV uniformly and get a homogeneous distribution. Second, another plan was optimised to achieve homogeneous . Both plans were calculated with and , and the differences between their dose distributions, clinical impact, and robustness were evaluated.
Uniform irradiation produced cold spots in bone (-4%) and implants (-10%). Uniform compensated them by increasing fluence but, when recalculated in , the fluence compensations produced higher doses that affected homogeneity. Additionally, doses were 1% higher for the target, and + 4% for the mandible, thus increasing toxicity risk. Robustness was impaired when increased fluence regions and heterogeneities mismatched.
Planning with as with can impact clinical outcome and impair robustness. In optimisation, uniform irradiation instead of homogeneous distributions should be pursued when media with different responses are involved. However, this requires adapting evaluation criteria or avoiding medium effects. Regardless of the approach, there can be systematic differences in dose prescription and constraints.
先前针对水模体剂量计算算法制定了放射治疗计划考量因素。先进算法提高了准确性，但其在介质对介质剂量方面的剂量值取决于所考虑的介质。本研究旨在展示用一种算法模拟另一种算法进行计划制定会如何引发新问题。
考虑一个涉及CTV外骨骼和金属异质性的头颈部病例。使用两种不同的商业算法来获取剂量分布和剂量分布。首先，优化一个计划以均匀照射PTV并获得均匀的剂量分布。其次，优化另一个计划以实现均匀的剂量分布。两个计划均使用剂量计算和剂量计算进行计算，并评估它们的剂量分布差异、临床影响和稳健性。
均匀照射在骨骼中产生冷点（-4%）和植入物中产生冷点（-10%）。均匀的剂量分布通过增加注量来补偿它们，但在剂量计算中重新计算时，注量补偿产生了更高的剂量，影响了均匀性。此外，靶区剂量高1%，下颌骨剂量高4%，从而增加了毒性风险。当增加的注量区域与异质性不匹配时，稳健性会受损。
像用剂量计算一样用剂量计算进行计划制定会影响临床结果并损害稳健性。在优化过程中，当涉及具有不同剂量响应的介质时，应追求均匀照射而非均匀的剂量分布。然而，这需要调整评估标准或避免介质效应。无论采用何种方法，剂量处方和限制可能存在系统差异。
