[Radiotherapy of tonsillar cancer. II. Tumor repopulation and normal tissue tolerance]

Clinical data of the 72 cases of squamous cell carcinoma of the tonsil irradiated with 60Co (results of treatment presented in the I part of this paper) have been used to analyse the importance of physical and biological factors influencing local control probability and risk of late effects in normal tissues. It was noted, that overall treatment time strongly influences tumour control but is less important for late effect of pharyngeal mucosa. With extension treatment time over 50 days, local control rate decreases dramatically almost to zero. Tumour response is less sensitive to change in dose per fraction than late responding pharyngeal mucosa. This suggestion is supported by high alpha/beta value of 25.0 Gy, calculated for cancer of the tonsil and relatively low alpha/beta value of 1.0 Gy for pharyngeal mucosa. Results suggest that improvement of local control of cancer of the tonsil with no increase in late complication rate might be expected using altered fractionation scheme, eg. accelerated hiperfractionation. This radiation treatment is based on dose per fraction less than 2.0 Gy, given in two fraction per day, in overall treatment time as short as possible.