Daily Online Adaptive Radiotherapy for Locally Advanced Cervical Cancer: Feasibility and Two-Year Outcomes of a prospective Phase II Study

Background Interfraction uterine motion necessitates internal target volume expansion, increasing bowel irradiation. Daily online adaptive radiotherapy may reduce margins and organ-at-risk dose while preserving target coverage. Methods In this prospective single-center phase II study, patients with FIGO 2018 stage IB3-IIIC1 cervical cancer received definitive chemoradiotherapy with weekly cisplatin and daily online adaptive intensity-modulated radiotherapy guided by cone-beam computed tomography. The pelvis received 45 Gy in 25 fractions, with a simultaneous integrated boost to 55 Gy in 25 fractions for involved lymph nodes. Clinical target volume and organs at risk were adapted daily; internal target volume expansion was omitted, and a 5-mm planning target volume margin was used. MR-guided adaptive brachytherapy was administered. The primary endpoint was acute gastrointestinal toxicity within 90 days after radiotherapy. Secondary endpoints included genitourinary and hematologic toxicity, dosimetry, treatment efficiency, and oncologic outcomes. Results Twelve patients (1 IB3, 8 IIB, 3 IIIC1) received 300 fractions; an adapted plan was selected in 298 fractions (99.3%). Acute grade ≥2 gastrointestinal toxicity occurred in 1 patient (8.3%). No late grade 2 or higher gastrointestinal or genitourinary toxicity occurred. The prespecified target-coverage goal (PTV D95%≥98%) was met in 89.7% of adapted fractions versus 17.3% of scheduled fractions; using the acceptable variation threshold (D95%≥95%), rates were 100% versus 43.7%. Mean adaptive session time was 19.7 minutes. At a median follow-up of 32.4 months (range, 25.5–41.3), no deaths or local failures occurred. One patient developed distant metastasis at 29.4 months after enrollment. Conclusions Daily online adaptive radiotherapy during definitive chemoradiotherapy for locally advanced cervical cancer achieved adequate target coverage and was associated with a low observed rate of clinically significant acute gastrointestinal toxicity, with local control maintained at 2 years.