Treatment at low dose rate, by low-LET radiation: present status and prospects

Patients with carcinoma of the oropharynx and buccal cavity received telecobalt gamma radiation therapy at low dose rate. Initially patients were treated by a single course of 65 Gy at the rate of 8 Gy per day. A spectacular tumour reduction both locally and in lymph nodes was observed but to minimise the side effects a split course therapy was introduced, i.e. 2 series of 32.5 Gy separated by an interval of 3 weeks. This resulted in markedly diminished mucosal reactions, virtually non-existent skin reactions and less frequent necroses which were only seen at the site of the primary tumour. The results of low dose rate therapy of a few cases of soft tissue sarcomas, tumours of the pelvis, oesophagus and pancreas are also given. Randomized trials between conventional fractionated irradiation and low dose rate irradiation of head and neck tumours are currently in progress. In addition a study of the upper limit of low dose rate to be applied has commenced. It is suggested that a comparison with other unorthodox techniques (neutrons and multi-fractionation) would be desirable. (U.K.)