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.