Optimizing Online Adaptation Timing in the Treatment of Locally Advanced Cervical Cancer

Abstract

Purpose/Objective: Online adaptive radiotherapy (ART) has emerged as a new treatment modality for cervical cancer. Daily online adapting improves target coverage and OAR sparing compared to traditional image-guided radiation therapy (IGRT); however, the required resources may not be feasible in a busy clinical setting. Less frequent adapting may still benefit cervical cancer patients due to large volume changes of the uterocervix of the treatment course. In this study, the dosimetry from different online adapt-on-demand schedules is compared.Materials/Methods: A retrospective cohort of 10 patients with cervical cancer treated with 260 fractions of definitive daily online adaptive radiotherapy was included. Plans with different adaptation schedules were simulated with adaptations weekly, every other week, once during treatment, and no adaptations (IGRT). These plans were applied to the synthetic CTs and contours generated during the patient's delivered daily adaptive workflow. The dosimetry of the weekly replan, every other week replan, once replan, and IGRT plans were compared using a paired t-test.Results: When compared to traditional IGRT plans, weekly and every other week ART plans had similar CTV coverage, but statistically significant improved sparing of OARs. Weekly and every other week ART had reduced bowel bag V40 by 1.57% and 1.41%, bladder V40 by 3.82% and 1.64%, rectum V40 by 8.49% and 7.50%, and bone marrow Dmean by 0.81% and 0.61%, respectively. Plans with a single adaptation had statistically significantly worse target coverage, and moderate improvements in OAR sparing. Of the 18 dose metrics evaluated, improvements were seen in 15 for weekly ART, 14 for every other week ART, and 10 for single ART plans when compared to IGRT. When every other week ART was compared to weekly ART, both plans had similar CTV coverage and OAR sparing with only small improvements in bone marrow dosimetry with weekly ART.Conclusions: This retrospective work compares different adapt on demand treatment schedules using data collected from patients treated with daily online adaptive radiotherapy. Results suggest weekly or every other week online ART is beneficial for reduced OAR dose compared to IGRT by exploiting the gradual changes in the uterocervix target volume.