CBCT-guided plan-of-the-day adaptive radiotherapy for locally advanced cervical cancer: Feasibility and dosimetric evaluation in a resource-limited setting.

Abstract

IntroductionInterfractional anatomical variations during pelvic radiotherapy for locally advanced cervical cancer may compromise target coverage and increase organ-at-risk (OAR) irradiation. This study evaluated the feasibility and dosimetric impact of a cone-beam CT (CBCT)-guided Plan-of-the-Day (PoD) adaptive radiotherapy where resources are limited.MethodsTwenty patients treated with definitive chemoradiotherapy were prospectively enrolled. Three volumetric modulated arc therapy (VMAT) plans were generated for each patient using planning target volume margins of 7, 10, and 15 mm around the cervical tumour clinical target volume. Daily CBCT imaging was used to select the most appropriate plan according to daily anatomy. The workflow was implemented using standard CBCT-guided IGRT resources without dedicated online adaptive radiotherapy software. Anatomical variations were assessed over 500 treatment fractions, and dose recalculation was performed on 410 fractions.ResultsSubstantial interfractional anatomical variations were observed. Bladder volume was lower than the planning value in 68.2% of fractions, whereas rectal distension exceeded planning values in 74.4%. The reduced-margin plan was selected in 58.8% of fractions, followed by the standard (27%) and large-margin plans (14.2%). Plan selection was significantly associated with bladder and rectal anatomical variations. Target coverage remained satisfactory across all plans (mean PTV V42.75Gy: 96.8-97.5%), with the predefined V95% criterion achieved in 85.7%, 79.8%, and 89.3% of recalculated fractions for the 7-, 10-, and 15 mm plans, respectively. Larger margins significantly increased bladder and rectal V30Gy and V40Gy values.ConclusionA CBCT-guided PoD strategy was feasible using standard IGRT resources and generally maintained high target coverage despite substantial interfractional anatomical variations. Larger margins increased OAR dose-volume parameters, supporting individualized daily plan selection where dedicated online ART infrastructure is unavailable.Implications for practiceCBCT-guided PoD offers a strategy where online adaptive radiotherapy is unavailable.