Application of LQ model to multifractionated radiotherapy

The radiotherapeutic ratio can be improved by rationalisation of fractionation regimes. Conventional fractionation in radiotherapy may not be the most optimal with respect to the cellular kinetics and radiosensitivity of proliferating tumour cells. We have tried hyperfractionated radiotherapy in cancer cervix and head and neck cases. In conventional fractionation (group I) 200 cGy per fraction to a total dose of 6000-7000 cGy was delivered. In multifractionated group, 2 fractions per day of 120 cGy per fraction (group II), 140 cGy per fraction (group III) and 160 cGy per fraction (group IV) with 4-6 hours interfraction interval were delivered. For assessment of dose required to produce tolerable normal tissue reactions, semiempirical formulae such as NSD, PT, TDF and CRE are being used but they have some limitations and hence the linear quadratic (LQ) model is being tried to describe the biological effects. We have estimated the α/β values for tumour regression by Boer's method (D Vs. dD plot) and they are 12.0 Gy for squamous cell carcinoma of head and neck and 11.2 Gy for cancer cervix. The results thus obtained have been compared with Boer's computer programme. (author). 13 refs., 1 fig., 6 tabs