Relapse Patterns After Flap-Sparing Postoperative Radiotherapy in Oral Cavity Cancer.

BACKGROUND: This study evaluates relapse patterns and treatment outcomes in oral cavity carcinoma (OCC) patients treated with flap-sparing radiotherapy (RT). METHODS: Patients treated with surgery and immediate free-flap reconstruction followed by RT due to OCC between 2018 and 2024 were analyzed retrospectively. During target volume delineation, the high-risk clinical target volume (CTV) was the native tissue-flap interface with an additional isotropic margin of 10 mm. We estimated the cumulative incidence and geometric patterns of local failures. RESULTS: Thirty-four patients matched the inclusion criteria. Median follow-up was 44 months. Three patients experienced local recurrences. Two relapses occurred at the native tissue-flap junction, with no intraflap failure. Three cases of Grade 3 acute oral mucositis, two cases of late Grade 3 dysphagia, and two cases of osteoradionecrosis of the jaw were observed. Clinically significant flap-related complication was not reported. CONCLUSION: No intra-flap local recurrence was observed after flap-sparing RT. The entire flap does not need to be intentionally covered in the CTV. Further investigation of planning optimization for the reconstructed flap is needed.