EFFECT OF TIME, DOSE AND FRACTIONATION ON LOCAL-CONTROL OF NASOPHARYNGEAL CARCINOMA

To study the effect of radiation factors on local control of nasophary ngeal carcinoma, 1008 patients with similarly staged T1N0-3M0 disease (He's classification) were retrospectively analyzed. All patients were treated by megavoltage irradiation alone using the same technique. Fo ur different fractionation schedules had been used sequentially during 1976-1985: with total dose ranging from 45.6 to 60 Gy and fractional dose from 2.5 to 4.2 Gy. The median overall time was 39 days (range = 38-75 days). Both for the whole series and 763 patients with nodal con trol, total dose was the most important radiation factor. The hazard o f local failure decreased by 9% per additional Gy (p < 0.01). Biologic al equivalents expressed in terms of Biologically Effective Dose or No minal Standard Dose also showed strong correlation. Fractional dose ha d no significant impact. The effect of overall treatment time was insi gnificant for the whole series, but almost reached statistical signifi cance for those with nodal control (p = 0.06). Further study is requir ed for elucidation, as 85% of patients completed treatment within a ve ry narrow range (38-42 days), and the possible hazard is clinically to o significant to be ignored.