title: Build-up and depth-dose characteristics of different fast neutron beams relevant for radiotherapy.
abstract: Build-up and central axis depth-dose curves have been obtained for d(50) + Be and d + T neutron beams. Measurements carried out with the collimator opening covered with a layer of lead showed that for all three neutron beams the entrance dose is approximately 60% of the dose at the maximum. Consequently the skin-sparing properties of these neutron beams will be approximately equal and comparable to those for electron beam therapy. Central axis depth-dose curves have been established for d(50) + Be neutrons at 129 cm SSD, for p(42) + Be neutrons at 125 cm SSD and d + T neurtons and 60Co gamma rays at 80 cm SSD. The 50% dose values in a water phantom are at depths of 12.7 cm, 12.0 cm, 9.7 cm and 12.7 cm respectively, for field sizes of approximately 15 cm x 20 cm. Insertion of a 6 cm thick nylon filter in the p(42)+Be beam increases this value from 12.0 cm to 13.5 cm. The gamma component for the d+T neutron beam is higher than for the cyclotron beams.
mesh_terms: D005214:Fast Neutrons / Q000627:therapeutic use*; D009502:Neutrons / Q000627:therapeutic use*; D011832:Radiation Injuries; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy; D012062:Relative Biological Effectiveness; D012867:Skin / Q000528:radiation effects