Time toxicity in CBCT-guided radiation therapy: A retrospective analysis of unplanned imaging burden across disease sites.

Purpose: Adaptive radiotherapy (ART) enhances treatment precision by adjusting for anatomical changes identified during a course of treatment. While ART is resource-intensive, non-adaptive workflows may also incur significant time and resource burden due to reactive interventions. This study aims to quantify the time-related burden of unplanned activities in non-adaptive CBCT-guided radiation therapy and assess their impact on patients and departmental efficiency. Methods and Materials: A retrospective analysis was conducted on 300 patients treated with CBCT-guided radiation therapy across 20 treatment techniques, encompassing 6,887 treatment fractions. Unplanned activities-including repeated CBCT acquisitions, aborted treatment sessions, additional CT scans, and mid-course replanning-were identified through electronic medical records and imaging logs. Time burden was estimated using electronic medical record timestamps. Results: Repeated CBCTs occurred in 55% of patients, contributing to 201.9 h of additional imaging time. Pelvic disease sites, particularly bladder and gynecologic cancers, exhibited the highest frequency of repeat imaging. Six patients required rescheduling due to unresolved anatomical discrepancies, and 15 underwent treatment plan modifications, with nine requiring repeat planning CTs. The average additional time per affected fraction was 13 min (range: 2-219 min), with some sessions extending beyond 3 h. Conclusions: Non-adaptive CBCT-guided workflows can lead to substantial time toxicity, comparable to or exceeding the resource demands of ART. These findings underscore the need for improved documentation, selective ART implementation, and workflow optimization to enhance patient experience and institutional efficiency.