A neutron-photon treatment planning intercomparison.

In order to assess different treatment philosophies in different neutron therapy centres as well as to gauge the quality of neutron dose distributions relative to corresponding photon plans, a neutron-photon treatment planning intercomparison has been organized amongst the neutron therapy centres in Europe and the U.S.A. Treatment plans were compared for patients with a tumour in the floor of the mouth, a carcinoma of the base of the tongue and a large bladder carcinoma. A wide variety in treatment plans was received. This was mainly caused by the different assumptions on the treatment margin around the tumour and whether or not the lymph nodes should be irradiated electively. Within the same institute, however, similar types of plans were used for both the neutron and the photon irradiations. The homogeneity of the adsorbed dose over the target volume can be made almost the same for photon and neutron irradiations, although this may require a more complicated technique for neutron treatment. The relative absorbed dose to normal tissues was somewhat higher for the neutron treatment. There is an increased chance of the occurrence of a hot spot with the relatively low energy neutron beams compared to the photon beams.