Dosimetry measurements at the fast neutron therapy facility in Seattle

The fast neutron therapy facility at the University of Washington has been in routine clinical use for 25 years. 50.5 MeV protons produce neutrons in a beryllium target mounted on an isocentric gantry. Beam shaping is accomplished with a 40-leaf collimator. Dosimetry measurements for treatment planning and calibration are performed with tissue equivalent ion chambers. A layered phantom of alternating Solid Water^® and Plastic Water^® slabs has been developed for rapid dose verification measurements. The neutron field in the room has been used for radiation testing of electronic components.