Assessment of risk factors associated with development of oronasal fistula as a late complication after carbon-ion radiotherapy for head and neck cancer.

Background: Oronasal fistulae (ONF) are one of the rare but serious complications of conventional photon radiotherapy. This study aimed to identify the risk factors for the development of ONF after carbon-ion radiotherapy (C-ion RT).

Materials And Methods: The data of 62 cases of sinonasal and oral cavity cancers treated with C-ion RT and followed-up in excess of 5 years were retrospectively reviewed. The correlation between the clinical and dosimetric parameters and the development of ONF was analysed.

Results: A total of 80.6% cases had sinonasal malignancies, and most tumours had advanced T stages (96.8%). Maxillary invasion was observed in 16 cases (25.8%), and malignant melanoma was the most common histology (46.8 %). All the cases received a dose of between 57.6 Gy (RBE) and 64 Gy (RBE) in 16 fractions over 4 weeks. At a median follow up of 88.8 months, 23 cases (37.1%) developed small localised ONF; however, none were of grade III severity. On separate multivariate analyses of clinical parameters in the entire cohort and in cases without maxillary invasion, the number of teeth irradiated with more than 50 Gy (RBE) was found to be the common significant independent risk factor for development of ONF.

Conclusion: The number of teeth irradiated with more than 50 Gy (RBE) is a significant independent risk factor for the development of ONF, which is a late complication of C-ion RT delivered in 16 fractions.