Impacts of different registration ranges on the accuracy of multiple metastases treated with tomotherapy

Objective: To analyze the impacts of different registration ranges on the accuracy of multiple metastases treated with helical tomotherapy. Methods: According to the locations of target volumes, 28 patients with multiple metastases were divided into the head/chest group (n = 15) and the chest/pelvis group (n = 13). The CT and MVCT images acquired in first fraction were studied and compared in two groups, which were captured and matched with different registration ranges (all targets/the targets in proximity to the head/the targets in proximity to the foot). The CTV_MVCT volume coverage rate (CR) under the matched target volumes, the dice similarity coefficient (DSC) between the CTV_CT and CTV_MVCT, and the position deviation of the CTV geometric center were compared. Results: We observed similar results in the head/chest group and chest/pelvis group. Specifically, there was no significant difference in the CR, DSC and geometric center deviation between the two target regions when registered with all targets (P > 0.05). Regarding single target region registration, the DSC and geometric center deviation of this target were significantly superior to the other non-registered target (P < 0.05). To a single target, the CR, DSC, and geometric center deviation obtained with registration presented the best performance, which was significantly greater than these parameters obtained with all targets registration, while the other side target area obtained the worst results (P < 0.05). Conclusions: Registration of one target region may reduce the accuracy of other non-registered targets. We recommend that the image guidance ranges for multiple metastases treated with tomotherapy should include all target regions or independent registrations for different targets. (authors)