Influence of fraction size, total dose, and overall time on local control of T1-T2 glottic carcinoma

Abstract

Purpose: To evaluate the influence of fraction size, overall time, total dose, and other prognostic factors on local control of T1 and T2 glottic carcinomas.

Methods and materials: Between 1956 and 1995, 398 consecutive patients with early glottic carcinoma (315 T1 and 83 T2) were treated with once-a-day definitive radiotherapy at the University of California, San Francisco, and associated institutions. Treatment was delivered 5 days per week. Minimum tumor dose ranged from 46.6 to 77.6 Gy (median: 63 Gy). The fraction size was < 1.8 Gy in 146; 1.8-1.99 Gy in 128; 2.0-2.24 Gy in 62, and > or = 2.25 Gy in 62 patients. Overall time ranged from 34 to 75 days (median: 50 days). The majority of patients treated with a fraction size of 2.25 Gy completed therapy within 43 days. Median follow-up of all alive patients was 116 months (range 3-436 months).

Results: Five-year local control was 85% for T1 and 70% for T2 glottic carcinomas (p = 0.0004). For T1 lesions, within the dose and time range evaluated, there was no apparent relationship between fraction size, overall time, total dose, and local control on multivariate analysis. Treatment era was the only significant prognostic factor (p = 0.02), and anterior commissure (AC) involvement was of borderline significance (p = 0.056). Five-year local control was 77% for patients treated between 1956-1970, 89% for between 1971-1980, and 91% for between 1981-1995; 80% for patients with AC involvement and 88% for those without. For T2 lesions, prognostic factors for local control on multivariate analysis were: overall time (p = 0.003), fraction size (p = 0.003), total dose (p = 0.01), impaired vocal cord mobility (p = 0.02), and subglottic extension (p = 0.04). Five-year local control was 100% for T2 lesions treated with overall time < or = 43 days vs. 84% for overall time > 43 days; 100% for fraction size > or = 2.25 Gy vs. 44% for fraction size < 1.8 Gy; 78% for total dose > 65 Gy vs. 60% for total dose < or = 65 Gy; 79% for normal cord mobility vs. 45% for impaired cord mobility, and 58% for lesions with subglottic extension vs. 77% for those without. The severe complication rate for the entire group was low: 1.8%.

Conclusions: Total dose, fraction size, and overall time were significant factors for local control of T2 but not T1 glottic carcinomas. Anterior commissure involvement was associated with decreased local control for T1 but not T2 lesions. For T1 lesions, local control improved over the treatment era. For T2 lesions, local control decreased with impaired cord mobility and subglottic extension.