Measurements on the radiation protection of patients irradiated with an 18-MeV electron linear accelerator.

In order to quantify the influence of some physical and geometrical treatment parameters on the stray radiation dose absorbed by patients undergoing radiotherapy on an 18-MeV linear accelerator, dose distributions were measured in a polystyrene phantom by means of LiF-dosimeters. For 10-MV X-rays, 6-MeV and 18-MeV electron radiation dose profiles, depth dose and isodose curves were obtained at various field sizes and treatment couch positions. By covering the phantom with 1 or 2 mm thick lead sheets a remarkable dose reduction was found. A two-exponential expression was derived to estimate stray radiation dosage in routine radiotherapy. The validity of the calculation method was demonstrated by comparing the gonadal load measured in an Alderson phantom with the calculated data.