Flap Sparing in Postoperative Radiotherapy of Oral Cavity Cancers

Patients with oral cavity cancer treated by reconstructive surgery with a flap. Patients will be treated in the study for : * Experimental arm: Post-operative radiotherapy with flap sparing * Control arm: Standard post-operative radiotherapy without flap sparing (current practice) Radiotherapy by IMRT using photons or proton therapy (IMPT)

Inclusion Criteria: * Patient aged 18 years or older * Performance Status 0-2 * Patient with oral cavity cancer (soft tissue or soft tissue-bone flap), treated by reconstructive surgery with a flap. Oropharynx cancer whose flap extends significantly into the oral cavity may be included in the study * Quality of resection with margins \> 1 mm * Patient candidate to post-operative radiotherapy (Intensity-Modulated Radiation Therapy (IMRT) or proton therapy) * Concomitant chemotherapy is allowed (stratification parameter) * Perioperative immunotherapy is allowed (neoadjuvant and/or adjuvant setting) * Patient must have signed a written informed consent form prior to any trial specific procedures * Patient affiliated to the social security system Exclusion Criteria: * Local flap (small size limiting IMRT modulation potential) * History of radiotherapy of head and neck area * Metastatic disease * History of other malignancy within the previous 3 years (except for appropriately treated in-situ cervix carcinoma and non-melanoma skin carcinoma) * Simultaneous participation in another clinical study may compromise the conduct of this study. * Pregnant or lactating women * Patient assessed by the investigator to be unable or unwilling to comply with the requirements of the protocol * Patient deprived of freedom or under guardianship