Patient-specific dosimetric impact of online adaptive radiotherapy for locally advanced cervical cancer

Background:When cervical cancer patients are treated with external beam radiation therapy, patient-specific anatomical changes, particularly bladder filling, alter the position and shape of the target volume throughout treatment. Online adaptive radiotherapy (oART) accounts for these interfractional changes by generating a treatment plan based on the patient's daily anatomy.Purpose:This study evaluated the dosimetric impact of oART and investigated the relationship between patient-specific anatomical changes and the dosimetric of benefit of adaptation using standard cone-beam CT (CBCT) images for locally advanced cervical cancer (LACC).Methods:Ten patients previously treated for LACC at our institution were identified. A reference treatment plan incorporating a 5 mm clinical target volume (CTV)-to-planning target volume (PTV) margin was generated within the planning system simulator. Three CBCT images (Fractions 1, 13, and 25) were used to retrospectively simulate an adaptive treatment session. For each CBCT, the reference plan was recalculated on the daily anatomy to generate a scheduled plan, and an adapted plan was generated for comparison based on target coverage and organ at risk (OAR) dose metrics. The relationship between interfraction anatomical variation and the dosimetric benefit of adaptation was evaluated.Results:Adapted plans improved target coverage while generally maintaining or reducing OAR dose relative to the scheduled plans. However, the magnitude of benefit from adaptation varied between patients. Moderate associations were observed between interfraction anatomical variation of the bladder volume change and improvements in target coverage.Conclusion:The dosimetric benefit of oART was patient-specific and was partially associated with interfraction anatomical variation. These findings support an individualized approach to identify patient-specific characteristics that may help determine what patients would benefit the most from adaptive radiotherapy.