Division of Clinical Radiology Service, Kyoto University Hospital, Kyoto, Japan.
Human Health Sciences, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
J Appl Clin Med Phys. 2020 Jan;21(1):110-116. doi: 10.1002/acm2.12805. Epub 2020 Jan 7.
To investigate the effects of interfractional variation, such as anatomical changes and setup errors, on dose delivery during treatment for prostate cancer (PC) and head and neck cancer (HNC) by courses of volumetric modulated arc therapy (VMAT) aided by on-treatment electronic portal imaging device (EPID) images.
Seven patients with PC and 20 patients with HNC who had received VMAT participated in this study. After obtaining photon fluence at the position of the EPID for each treatment arc from on-treatment integrated EPID images, we calculated the differences between the fluence for the first fraction and each subsequent fraction for each arc. The passing rates were investigated based on a tolerance level of 3% of the maximum fluence during the treatment courses and the correlations between the passing rates and anatomical changes.
In PC, the median and lowest passing rates were 99.8% and 95.2%, respectively. No correlations between passing rates and interfractional variation were found. In HNC, the median passing rate of all fractions was 93.0%, and the lowest passing rate was 79.6% during the 35th fraction. Spearman's correlation coefficients between the passing rates and changes in weight or neck volume were - 0.77 and - 0.74, respectively.
Analyses of the on-treatment EPID images facilitates estimates of the interfractional anatomical variation in HNC patients during VMAT and thus improves assessments of the need for re-planning or adaptive strategies and the timing thereof.
通过容积调强弧形治疗（VMAT）治疗过程中的电子射野影像装置（EPID）图像，研究分次内变化（如解剖结构变化和摆位误差）对前列腺癌（PC）和头颈部癌（HNC）治疗中剂量分布的影响。
本研究纳入了 7 例接受 VMAT 治疗的 PC 患者和 20 例 HNC 患者。从治疗期间的整合 EPID 图像中获取每个治疗弧在 EPID 位置的光子通量后，我们计算了每个弧的第一分次与后续分次之间的通量差异。根据治疗过程中最大通量的 3%的容限水平，调查了通过率，并研究了通过率与解剖结构变化之间的相关性。
在 PC 中，中位通过率和最低通过率分别为 99.8%和 95.2%。未发现通过率与分次间变化之间存在相关性。在 HNC 中，所有分次的中位通过率为 93.0%，第 35 分次的最低通过率为 79.6%。通过率与体重或颈部体积变化之间的 Spearman 相关系数分别为-0.77 和-0.74。
分析治疗期间的 EPID 图像有助于评估 HNC 患者在 VMAT 过程中的分次内解剖变化，从而更好地评估重新计划或自适应策略的必要性及其时机。
