[Prognostic factors for oral tongue carcinoma treated with intra-oral cone electron beam irradiation].

Twenty-five patients with squamous cell carcinoma of the oral tongue were treated with intra-oral cone electron beam irradiation (IOC) during the period from 1985 to 1995. We analyzed the prognostic factors for local control and complications. IOC was applied for T1 (16 cases) and T2 (9 cases) tumors. Hypofractionation was used for IOC (20, 10, or 8 Gy/fr, 1f/wk). The total dose delivered ranged from 40 Gy to 78 Gy. Radiation dose homogenization was done through calculation of the normalized total dose (NTD) for alpha/beta = 10 (tumor) and alpha/beta = 3 (late normal tissue). The two-year local control rates for T1 and T2 were 80.4% and 77.8%, respectively. The two-year local control rates for patients whose overall treatment time (OTT) was < or = 28 days (n = 16) was 100% vs. 41.7% for patients whose OTT was > 28 days (n = 9) (p = 0.002). Multivariate analysis was applied to identify possible prognostic factors for local control. OTT (p = 0.02) was the only variable that significantly influenced local control. The incidence of radiation ulcer was 33.3% (7/21). Significant indicators of ulceration were fraction size (>> 10 Gy) and NTD (alpha/beta = 3) (>> 130 Gy) (p < 0.05). These results indicate that prolonged OTT was the major reason for the failure of IOC radiotherapy to control local disease and that the relatively high rate of ulceration was due to large fraction size and high NTD (alpha/beta = 3).