SIMILAR DECREASES IN LOCAL TUMOR-CONTROL ARE CALCULATED FOR TREATMENTPROTRACTION AND FOR INTERRUPTIONS IN THE RADIOTHERAPY OF CARCINOMA OFTHE LARYNX IN 4 CENTERS

Purpose: Data on patients with cancer of the larynx are analyzed using statistical models to estimate the effect of gaps in the treatment ti me on the local control of the tumor, Methods and Materials: Patients from four centers, Edinburgh, Glasgow, Manchester, and Toronto, with c arcinoma of the larynx and treated by radiotherapy were followed up an d the disease-free period recorded, In all centers the end point was c ontrol of the primary tumor after irradiation alone, The local control rates at greater than or equal to 2 years, P-c, were analyzed by log linear models, and Cox proportional hazard models were used to model t he disease-free period, Results: T stage, nodal involvement, and site of the tumor were important determinants of the disease-free interval, as was the radiation schedule used, Elongation of the treatment time by 1 day, or a gap of 1 day, was associated with a decrease in P-c of 0.68 % per day for P-c = 0.80, with a 95 % confidence interval of (0.2 8, 1.08)%. An increase of 5 days was associated with a 3.5% reduction in P-c from 0.80 to 0.77, At P-c = 0.60 an increase of 5 days was asso ciated with an 7.9% decrease in P-c. The time factor in the Linear Qua dratic model, gamma/alpha, was estimated as 0.89 Gy/day, 95% confidenc e interval (0.35, 1.43) Gy/day, Conclusions: Any gaps (public holidays are the majority) in the treatment schedule have the same deleterious effect on the disease free period as an increase in the prescribed tr eatment time, For a schedule, where dose and fraction number are speci fied, any gap in treatment is potentially damaging, (C) 1998 Elsevier Science Inc.