Patrick H M, Poon E, Kildea J
Medical Physics Unit, McGill University, Montreal, Québec, Canada.
Department of Medical Physics, McGill University Health Centre, Montreal, Québec, Canada.
Acta Oncol. 2023 Aug;62(8):915-922. doi: 10.1080/0284186X.2023.2238556. Epub 2023 Jul 28.
Dose-surface maps (DSMs) are an increasingly popular tool to evaluate spatial dose-outcome relationships for the rectum. Recently, DSM addition has been proposed as an alternative method of dose accumulation from deformable registration-based techniques. In this study, we performed the first experimental investigation of the accuracy at which DSM accumulation can capture the total dose delivered to a rectum's surface in the presence of inter-fraction motion.
A custom PVC rectum phantom capable of representing typical rectum inter-fraction motion and filling variations was constructed for this project. The phantom allowed for the placement of EBT3 film sheets on the representative rectum surface to measure rectum surface dose. A multi-fraction prostate VMAT treatment was designed and delivered to the phantom in a water tank for a variety of inter-fraction motion scenarios. DSMs for each fraction were calculated in two ways using CBCT images acquired during delivery and summed to produce accumulated DSMs. Accumulated DSMs were then compared to film measurements using gamma analysis (3%/2 mm criteria). Similarity of isodose clusters between films and DSMs was also investigated.
Baseline agreement between film measurements and accumulated DSMs for a stationary rectum was 95.6%. Agreement between film and accumulated DSMs in the presence of different types of inter.-fraction motion was ≥92%, and isodose cluster mean distance to agreement was within 1.5 mm for most scenarios. Overall, DSM accumulation performed the best when using DSMs that accounted for changes in rectum path orientation.
Dose accumulation performed with DSMs was found to accurately replicate total delivered dose to a rectum phantom in the presence of inter-fraction motion.
剂量-表面图（DSM）是一种越来越流行的用于评估直肠空间剂量-结果关系的工具。最近，有人提出将DSM叠加作为基于可变形配准技术的剂量累积的替代方法。在本研究中，我们首次进行了实验研究，以评估在存在分次间运动的情况下，DSM累积能够捕获传递到直肠表面的总剂量的准确性。
为该项目构建了一个定制的PVC直肠模体，该模体能够模拟典型的直肠分次间运动和充盈变化。该模体允许在代表性的直肠表面放置EBT3胶片来测量直肠表面剂量。设计了一种多分次前列腺VMAT治疗方案，并在水箱中针对各种分次间运动场景将其施用于模体。使用在治疗过程中采集的CBCT图像以两种方式计算每个分次的DSM，并将其相加以生成累积DSM。然后使用伽马分析（3%/2毫米标准）将累积DSM与胶片测量结果进行比较。还研究了胶片和DSM之间等剂量簇的相似性。
静止直肠的胶片测量结果与累积DSM之间的基线一致性为95.6%。在存在不同类型的分次间运动时，胶片与累积DSM之间的一致性≥92%，并且在大多数情况下，等剂量簇到一致性的平均距离在1.5毫米以内。总体而言，当使用考虑直肠路径方向变化的DSM时，DSM累积表现最佳。
发现在存在分次间运动的情况下，用DSM进行的剂量累积能够准确复制传递到直肠模体的总剂量。
