Postoperative radiotherapy delineation after mandibular bone flap reconstruction in oral cavity and oropharyngeal cancers.

BACKGROUND

Postoperative radiotherapy is a cornerstone of management for locally advanced oral cavity and oropharyngeal cancers. Increasing use of vascularised mandibular bone flaps and patient-specific fixation systems has substantially modified postoperative anatomy, thereby complicating target volume delineation. While consensus guidelines exist for soft tissue flaps, no practical framework specifically addresses mandibular bone flap characterisation and delineation in poRT planning. We aimed to provide multidisciplinary, imaging-based recommendations for bone flap delineation on planning CT.

METHODS

Representative cases of segmental, marginal and mandibulotomy resections were identified from the multicentre XFLAP database. Practical recommendations were developed regarding CT windowing, identification of osteotomies and vascular pedicles, and separate contouring of native mandible, bone flap, osteotomies, fixation hardware and associated soft tissue components jointly by head-and neck-surgeons, radiation oncologists and radiologists.

RESULTS

Mandibular reconstruction generates heterogeneous anatomical scenarios, including multi-segment fibular reconstructions, load-bearing plates without osseous continuity, marginal resections, and mandibulotomies. We propose systematic use of adapted bone and metal windowing for accurate identification of cortical interfaces and hardware; independent delineation of the bone flap distinct from the native mandible; and separate contouring of osteotomy sites and fixation plates to enable regional dose-volume analysis.

CONCLUSION

Mandibular bone flap reconstruction introduces additional complexity in the poRT setting. Standardised, anatomy-driven delineation of bone flaps, osteotomies and metallic hardware on planning CT may represent a necessary step toward reproducible treatment planning and systematic evaluation of dose-volume effects in reconstructed mandibles. These recommendations provide a practical foundation for harmonisation across institutions and for future flap-sparing strategies.