Early skin reactions in head and neck malignancy treated by twice-daily fractionated radiotherapy--estimation of alpha/beta of LQ model.

Conventional radiotherapy, the five times a week regime, fails to achieve locoregional control in a large proportion of advanced carcinomas of head and neck and cervix. Different non-conventional fractionation schedules are being investigated to improve the tumour control rate but, during treatment of advanced malignancy with curative intent, it is seldom possible to deliver a radical dose to the tumour because of the constraint of inducing irreparable normal tissue complications. To compare the probability of occurrence of normal tissue damage and gain in therapeutic ratio various empirical models such as NSD, TDF, CRE and TSD have been suggested, and recently the linear quadratic (LQ) model has been gaining popularity and is claimed to be superior to earlier empirical models. We have studied twice-daily fractionated schedules in head and neck malignancy with the aim of estimating the alpha/beta value of the LQ model for early acute skin effects, and found it to be 9.16 Gy, 7.66 Gy and 8.59 Gy for mild erythema, intensive erythema and dry desquamation respectively.