Radiotherapy with 6-megavolt photons for early glottic carcinoma: potential impact of extension to the posterior vocal cord.
PURPOSE: Radiation therapy has a high success rate in the treatment of early glottic carcinoma. Excellent outcomes have been reported from centers using cobalt-60 or relatively low-energy (< or = 4 MV) radiation therapy to achieve these results. Whether similar outcomes can be achieved with a 6 MV linear accelerator has been less rigorously evaluated. This study assesses the efficacy of 6 MV radiation therapy for early stage glottic cancer and identifies prognostic factors for local control and overall survival in this common disease. MATERIALS AND METHODS: One hundred twenty-eight consecutive cases of Tis, T1, and T2 squamous cell carcinomas of the glottis from 1982 to 1996 were retrospectively analyzed with regard to local control and survival. All patients were treated with definitive radiation therapy with a 6-MV linear accelerator. Potential prognostic factors for local control and survival were evaluated with univariate and multivariate models. Median follow-up of locally controlled patients was 65 months. RESULTS: The overall 3-year actuarial local control rates for T1 and T2 carcinomas were 86% and 68%, respectively. Patients with lesions involving the posterior third of the vocal cord had significantly worse 3-year local control (76% vs. 86%, P =.038). Radiation therapy technique and overall treatment time did not significantly affect local control. For patients with Tis and T1 lesions, factors associated with significantly worse local control included cordectomy-ineligible disease (P =.024), dose less than 6,600 cGy (P =.024), and lesions limited to the posterior third of the vocal cord (P =.004). Three-year local control was 76%, with doses less than 6,600 cGy and 90% with higher doses. High rates of second primary malignancies were observed and represented the major cause of death. Five-year overall survival was 84%. CONCLUSIONS: The use of 6-MV photons for treatment of early glottic cancer seems to achieve local control similar to that reported with lower-energy photons. However, patients with posterior third involvement had a poorer local control rate with standard radiation therapy, thereby suggesting that alternative approaches be considered.