Secondary exposure for 73 and 200 MeV proton therapy

Following modifications on the beam line at the Orsay Proton-therapy Center, dose measurements were performed in order to make a dose map in the treatment rooms and in the delimited radiation-controlled area around beam line. Measurements were performed using tissue-equivalent proportional counters and rem-counters. Analysis of TEPC single event measurements showed that high LET components (<10 keV.μm-1) represent 90 to 99% of total dose equivalent in the treatment rooms and 50 to 90% in the controlled area and quality factors range, respectively between 2 and 15. A fast neutron component was identified in the treatment rooms, where dose equivalent rate varied between few μSv.h-1 to some dozen of mSv.h-1. In high-energy radiation field rem-counters underestimated TEPC values for neutron component. The variation between instruments response according to the location is linked to energetic spectrum variations and instrument characteristics. (authors)