Do overall treatment time, field size, and treatment energy influence local control of T1-T2 squamous cell carcinomas of the glottic larynx?

Purpose: To evaluate treatment and patient related prognostic factors that may influence local control in the treatment of T1-T2 squamous cell carcinoma of the glottic larynx. Methods and Materials: One hundred nine patients with invasive, previously untreated T1-T2 squamous cell carcinoma of the glottic larynx were treated with curative intent with radiotherapy at the Fox Chase Cancer Center between June 1980 and November 1991. Follow-up ranged from 26-165 months (mean 83 months). Results: The 2-year local control rates for patients with T1 and T2 lesions were 89% and 80%, respectively. The 2-year local control rate for patients whose overall treatment time was < 50 days was 92% vs, 82% for patients whose overall treatment time was > 50 days (p = 0.07). The 2-year local control rate for patients treated with an irradiated area < 36 cm(2) was 90% compared to 86% in patients who were treated to an area greater than or equal to 36 cm(2). The 2-year local control rate for patients treated with Co-60 was 83% vs. 92% for patients treated with 6 MV x-ray. Cox proportional hazards regression analysis was performed using the following variables: treatment energy, irradiated area, gender, tobacco pack years, tumor differentiation, overall treatment time, total dose, dose per fraction, and T stage. Overall treatment time (p = 0.05) was the only variable that significantly influenced local control, Conclusion: Extending the overall treatment time was found to adversely influence local control, Neither the irradiated area nor treatment energy was found to influence local control in early stage vocal cord carcinoma.