Depth-dose measurements of d-T neutrons for radiotherapy applications.

In connection with clinical applications of fast neutrons, depth-dose measurements have been carried out for collimated 15 MeV neutron beams at various source-to-skin distances, using different phantoms of the upper part of the human body. The distribution of fast, thermal and intermediate neutron dose or kerma and gamma dose over the phantoms was determined with tissue-equivalent ionization chambers, gold foils with and without cadmium covers and a shielded Geiger-Müller counter, respectively. In order to determine the tumour dose and the exit dose for the irradiation of patients with pulmonary metastases, depth-dose measurements have been performed for an inhomogeneous phantom containing lung-equivalent material. The measurements indicate a considerable difference in depth dose with respect to the dose distribution in a homogeneous phantom. Measurements with sulphur activation detectors to monitor the exit dose are discussed and compared with the results obtained in the actual patient irradiations.