Sensitivity of human squamous cell carcinoma of the larynx to fractionated radiotherapy.

Data obtained for the response of tumours from two multicentre clinical trials of the British Institute of Radiology have been combined and studied. Both trials involved patients with laryngopharyngeal carcinoma. There were 734 patients in the first trial, recruited between 1965 and 1975, and 611 patients in the second trial, recruited between 1975 and 1985. Observed survival and tumour-free rates for all patients are calculated. T-class and the nodal status of the patient at the start of the treatment were important factors in the determination of both observed survival and tumour-free rates. Overall treatment time was an important factor in determining the recurrence of tumour. The longer the overall treatment time the greater was the chance of tumour recurrence. The linear-quadratic (LQ) model was used in the analysis of the tumour recurrence data for a large group of patients with laryngeal tumours without nodal involvement. A small alpha/beta ratio of 0.94 Gy was obtained for T3 tumours while that of T2 tumours was negative, -10.5 Gy. The value for T1 tumours was higher at 23 Gy. However, use of the LQ model with a time component increased the alpha/beta ratios to 26.0 +/- 27.20 Gy, 18.0 +/- 12.33 Gy and 13.38 +/- 5.40 Gy for T1, T2 and T3 tumours, respectively. The time component, the gamma/alpha ratios, for these tumours were 0.15 +/- 0.27 Gy/day, 0.81 +/- 0.18 Gy/day and 0.76 +/- 0.15 Gy/day, respectively.