Moderately Hypofractionated Online Adaptive Radiotherapy for Cervical Cancer: A Prospective Study of Feasibility, Acute Toxicity and Dosimetric Benefits

Background/Objectives: Moderately hypofractionated radiotherapy (MHRT) may shorten treatment duration for cervical cancer but raises concerns regarding toxicity due to substantial interfractional pelvic organ motion. This prospective study evaluated the feasibility, workflow efficiency, dosimetric benefits, and acute toxicities of daily online adaptive radiotherapy (oART)-guided MHRT. Methods: Thirty patients with FIGO 2018 stage IB1–IIB or IIIC1 cervical squamous cell carcinoma receiving definitive chemoradiotherapy were prospectively included between September 2023 and April 2024 (NCT05994300). All patients underwent daily oART, receiving 43.35 Gy in 17 fractions to the pelvic target volume, with a simultaneous integrated boost to 54.40 Gy in 17 fractions for involved lymph nodes. The adaptive workflow consisted of iterative cone-beam computed tomography acquisition, artificial intelligence-assisted contouring, physician review, plan adaptation, and treatment verification. Workflow efficiency, plan selection, target coverage, organ-at-risk (OAR) sparing, treatment completion, early tumor response and acute toxicity were prospectively assessed. Results: A total of 510 adaptive fractions were delivered. The first-attempt adaptation success rate was 99.0%, and adapted plans were selected in 99.4% of fractions. The mean adaptive workflow and total treatment times were 17.3 and 23.3 min per fraction, respectively. Compared with scheduled plans, adapted plans significantly improved target coverage, with V100% increasing by 7.26% for the planning target volume of the uterus and 8.79% for planning target volume of the cervix (both p < 0.001), while significantly reducing doses to the bladder, rectum, small bowel, bone marrow, and femoral heads. All patients achieved complete clinical response at 3 months. Acute toxicity was generally manageable; Grade ≥ 3 gastrointestinal, genitourinary, and hematologic toxicities occurred in 10%, 0%, and 40% of patients, respectively, including one Grade 4 neutropenia event, and no treatment interruptions. Conclusions: Daily oART-guided MHRT was feasible and efficient, providing improved target coverage and reduced OAR doses compared with scheduled plans. Acute toxicity was acceptable. These findings provide early prospective evidence supporting the feasibility of this treatment strategy and warrant further validation in larger prospective studies with longer follow-up.