Importance of dose per fraction and estimation of an alpha/beta value for the late complications of the vocal cord.

The incidence of late complications for different sizes of dose per fraction is analysed in 208 cases with squamous cell carcinoma of the vocal cord. The series comprised 156 cases with T1N0M0 and 52 cases with T2N0M0 lesions. Radical radiotherapy was given with three different regimens having dose per fraction of 3.33 Gy, 2.5 Gy and 2.25 Gy. There were 46 cases of late radiation induced laryngeal oedema. Using this clinical data an alpha/beta value of 2.35 +/- 0.13 Gy was estimated for late complications of the vocal cord. It was found that there is strong correlation between size of dose per fraction and the risk of late complication in the vocal cord.