A Low Cost/Low Intensity 50 MeV Proton Irradiation Facility

Protons have been proposed as one of the most useful particles for radiation therapy, but have found limited use due to the cost and scarcity of medium energy proton accelerators. However the highly successful program on the Harvard Cyclotron has increased interest in expanding the number of treatment Facilities. In order to demonstrate that high intensity proton accelerators are not required and to gain experience with treating patients using protons, a low cost and low intensity source of of 50 MeV protons was developed at Argonne. Although the beam penetration is limited to 22 mm, the beam is capable of treating a major fraction of the ocular melanoma tumors treated at the Harvard Cyclotron. This beam operates parasitically with the Rapid Cycling Synchrotron at Argonne using a source of 50 MeV H° atoms which are produced by stripping in the gas of the 50 MeV H- linear accelerator. A stripping fraction of about 3-5 × 10-5 is observed and yields a 0.4 namp beam of protons. Results on the properties and operation of this parasitic beam are presented.