An investigation into the clinical effects of fast neutrons

Abstract

The early observations on 35 patients treated since November, 1969 with fast neutrons from the M.R.C.'s cyclotron at Hammersmith Hospital are described, together with the methods used to select a practical therapeutic regime, investigate the effects of bolus, skin sparing and determine the RBE for skin. Eighteen patients required radiation to more than one area and these treatments were given by both high and low LET radiations. The skin reactions produced were compared by a system of skin scoring and the tumour responses by measurements made as objectively as possible. The dose-rate of 40 rads per minute resulted in treatment times of less than four minutes per field and enabled patients to be treated in the kneeling and sitting as well as the lying position. This flexibility overcame the disadvantages of the fixed horizontal beam. Collimation of the beam was good and wedged filters could be used as in conventional radiotherapy. Doses received by the eyes were approximately 1 rad per 1,000 rads to the treatment area. The RBE for skin for neutrons at 120 rads per fraction appears to be 2·9. There was a clinically significant skin sparing effect. 1,440 rads of neutrons in 12 fractions over 26 days to a 90 cm2 area was a practical therapeutic regime and caused a skin reaction which healed in all cases and also caused satisfactory tumour regression.