Effect of treatment time on outcome of radiotherapy for oral tongue carcinoma.

Purpose: To investigate the importance of total treatment time on the outcome of external beam radiotherapy (EBRT) followed by internal brachytherapy for the treatment of oral tongue carcinoma.

Methods And Materials: Ninety-four patients with T1-T2N0 squamous cell carcinoma of the oral tongue were treated using 35-40 Gy EBRT followed by 35-40 Gy interstitial (137)Cs brachytherapy between 1985 and 1995. The interval between the end of EBRT and the start of interstitial treatment varied for numerous unavoidable reasons, with a mean of 25.3 days and standard deviation of 3.5 days. The median follow-up period was 59.1 months (range 6-146).

Results: The actuarial survival rate of all cases was 78.4% at 5 years. The 5-year local control rate for those with T1 and T2 was 92.8% and 62.7%, respectively (p < 0.05). The local control rate of the primary tumor in patients with a total treatment time >43 days was statistically lower than that of patients with a total treatment time < or =43 days in all patients (p < 0.05) and in the subgroup of Stage T2 patients (p < 0.05). Multivariate analysis revealed that the local control rates in all cases were significantly related to the T stage (T2 or not), total treatment time (>43 days or not), and location of disease (posterior or not). Regression analysis for 5-year local control as a function of treatment duration showed a 2% loss of local control per day of treatment extension >30 days (r = 0.94, p < 0.01).

Conclusion: The total treatment time was associated with the local control rate in the RT of oral tongue carcinoma. The loss in local control was estimated to be 2.0% per additional day in our series for oral tongue carcinoma.