DOSE, FRACTIONATION AND OVERALL TREATMENT TIME IN RADIATION-THERAPY -THE EFFECTS ON LOCAL-CONTROL FOR CANCER OF THE LARYNX

The effect of total tumor dose, split course treatment and overall tre atment time on local control was analysed in a retrospective series of 997 patients with carcinoma of the larynx, treated with megavoltage r adiotherapy only. Primary tumors were classified by site (glottis and supraglottis) and T-stage. Continuous course (CC, n = 594) treatment w as given primarily to small tumors. Split course radiation (SC, n = 40 3) was generally given to patients with larger field sizes. Total dose s of irradiation ranged from 50 to 79 Gy, with a mean of 64 Gy in CC a nd 66 Gy in SC. Most of the treatments were given with fraction sizes between 2.0 and 2.1 Gy (91%). Overall treatment times ranged between 2 5 and 60 days in the CC group (mean, 45 days) and between 45 and 120 i n the SC group (mean, 76 days). A local recurrence was observed in 256 patients. T-stage was the only tumor characteristic strongly related to local failure. Corrected for T-stage, no difference in local relaps e rate was observed between glottic and supraglottic tumors, or betwee n node-negative (n = 886) and node-positive patients (n = 111). After correction for T-stage the local failure rate of SC-treated tumors was 2.1 (95% confidence limits: 1.4-3.1) times higher than of CC-treated tumors. However, this effect could not be explained as an effect of th e overall treatment time (OTT) itself, as no effect of OTT was found w ithin the SC and the CC group, even though the variation in OTT's was considerable in the SC group. A higher tumor dose was associated with a lower local failure rate in the CC group (p = 0.005), but not in the SC group (p = 0.56).