ACTIVATION OF A 250 MEV SC-CYCLOTRON FOR PROTON THERAPY

Abstract

Beam losses in dedicated 230-250 MeV cyclotrons for<br />proton therapy cause radioactivity in machine parts. A<br />systematic study has been performed of the activation of<br />PSI&rsquo;s 250 MeV SC-cyclotron for proton therapy. Since<br />the start of the cyclotron operation dose rate<br />measurements have been made as a function of time at<br />several locations in and around the cyclotron. Gamma ray<br />spectra have been measured of selected iron inserts in the<br />pole and of copper disks in the liner of the RF system.<br />The isotopic composition of the activation has been<br />derived and compared with activations calculated with<br />Monte Carlo calculations (MCNPX). The data and beam<br />history of the cyclotron allow predictions of the dose rate<br />during service activities shortly after beam interruption as<br />well as after a specified period of operation