Post-operative brachytherapy: a prognostic factor for local control in epidermoid carcinomas of the mouth floor

The aim of this study was to analyse the role of post-operative brachytherapy (BT) in a group of patients with a high risk of local relapse (positive or narrow surgical margins) for squamous cell carcinoma of the mouth floor (SCCFM). A comparison with post-operative external beam irradiation (EBI) in a group of patients with standard risk of local relapse for SCCFM with free margins is performed to estimate the benefit of BT. From 1979 to 1992, an initial group of 32 patients with SCCFM (12, T1-2; 20, T3-4x) received an Ir 192 low dose rate BT using plastic tubes (+EBI for 20 patients) after surgery with positive or close margins. BT was applied in one or two planes to the surgical scar. The mean dose of BT was 57 Gy (range: 50-60) for exclusive BT and 22 Gy (range: 15-30) when a boost was applied (mean EBI dose = 50 Gy). During the same period, 36 patients had post-operative external irradiation alone after satisfactory surgical resection. Excluding the post-operative margin, these two groups were comparable for other prognostic factors. The mean follow-up was 46 months (range: 5-145) with a minimum follow-up of 2 years. For BT and EBI groups, the 5-year results (Kaplan-Meier) were, respectively, overall survival 62% and 43%, local control 81% and 60% (P = 0.09) (log-rank) and severe complications 4/32 and 1/36. Post-operative BT achieves good local control for patients with narrow or positive margins by increasing the dose to the surgical scar, with good tolerance. Given these encouraging results, we confirm this treatment for these patients.