CBCT-Guided Online Adaptive Radiotherapy In the Treatment of Cervical Cancers
Abstract
Purpose
To quantify the efficacy of CBCT-guided external beam online adaptive radiotherapy (oART) compared to conventional cervical cancer treatment methods, and to determine the impact of intrafraction anatomical motion on dosimetry.
Methods
Ten retrospective cervical cancer patients treated with oART on Varian’s Ethos were analyzed. Of the 25 total treatment sessions, sessions 1, 5, 10, 15, 20, and 25 were evaluated to represent how patient anatomy evolves over the course of treatment. Basic and intermediate image-guided radiotherapy (IGRT) plans were optimized in the Eclipse treatment planning system following the specifications from the EMBRACE II protocol. Basic and intermediate IGRT dosimetry were compared to the delivered oART dosimetry using dose-volume histogram (DVH) metrics for both targets (primary and nodal clinical target volumes, and nodal gross tumour volumes) and nearby organs-at-risk (OARs; bladder, rectum, and bowel). Additionally, changes in dosimetry between the initial and verification CBCT scan taken post-adaptation prior to beam delivery were assessed to quantify the impact of intrafraction anatomical motion occurring during the 10-45 minutes required for oART treatment planning.
Results
Compared to conventional IGRT methods, oART improved target coverage, increasing the target volume receiving the prescribed dose by an average of 7.5%, while lowering the dose to the bowel and rectum. oART also increased the probability of meeting target and OAR clinical criteria by up to 76.6%. While intrafraction motion due to bladder filling and rectal changes was found to compromise target coverage and increase the dose received by OARs, these changes were not dosimetrically significant as they remained within the range of clinical acceptability.
Conclusion
This work indicates that oART is dosimetrically superior to conventional cervical cancer treatment techniques and should be integrated into clinical workflows when feasible. Additional work should be conducted to enhance the oART workflow and minimize the impact of intrafraction anatomical motion.