Verification of dose contribution due to short range secondary particles produced by high energy charged particles measured with CR-39
小平, 聡 ,
小西, 輝昭 ,
北村, 尚 ,
内堀, 幸夫Benton, Eric
In addition to energy loss bay ionization process, protons of energy >~50 MeV, such as those used in proton radiotherapy, can undergo nuclear interactions with nuclei of Z >1, resulting in the production of short range (<10 μm), high-LET (liner energy transfer) target fragment particles. One of the few methods to detect these short-range particles is by means of CR-39 plastic nuclear track detector analyzed with an atomic force microscope. However, doe to the LET-dependent angular sensitivity of CR-39, multiple detectors exposed at a range of incident angles to the primary proton beam, must be analyzed in order accurately detemine the LET spectrum, absorbed dose and dose equivalent. The LET spectrum of 160MeV proton induced secondary particles was exprrimentally measured with CE-39, which were exposed at six different incident angles to take into account the intrinsic sensitivity of the critical angle for track registration. The irradiated detectors were chemically processed to remove a 1 μm thick volume of CR-39, The measured LET range of short range tracks was from 15keV/μm up to 1.5MeV/μm. The absorbed dose contribution (Ds/Dp) from secondary particles to primary proton dose was ~1%, while the dose equivalent contribution (Hs/Dp) was found to be ~20%.