Dosimetric investigations in the dose buildup using bolus techniques for fast neutron therapy

A moulded bolus is commonly used to compensate for contour irregularities of patients treated with fast neutrons. The bolus material should have the same attenuation characteristics as tissue, should be easily mouldable and sufficiently solid for multiple applications. For fast neutron beams, the mixture of equal parts of beeswax and paraffin is a suitable bolus material. As in photon beams the bolus, when placed directly on the patient skin, removes completely the skin sparing effect. However, in neutron beams the dose buildup can mostly be recovered by lining the bolus surface in contact with the patient with a thin layer of lead. This paper presents dosimetric investigations in the dose buildup of a collimated 14-MeV DT-neutron beam underneath the surface of a solid phantom behind a 1.0-cm layer of bolus material lined with 0.03 cm of lead. It is shown that most of the dose buildup of the bolus-free neutron beam can be recovered.