TL Dosimetry in High LET Radiotherapeutic Fields

Abstract

A typical therapeutic high LET particle field is generated from overlapping beams of different ranges and directions. The LET contributions vary across the field, which leads to different biological effectiveness and therefore has to be accounted for in the treatment planning. The dosemeters employed have to generate the dose information independent of LET and give some information on the LET composition. They also should be very small in order not to change the range of the particles considerably. TL dosemeters have been considered for use in such fields because of their small size, high sensitivity and their possible use as in vivo dosemeters. The sensitivity of most materials, however, decreases with increasing LET. But in some materials with two well separated glow peaks like CaF 2 :Tm or LiF the efficiency of one of the peaks either increases with increasing LET or remains constant up to a certain LET value. Such materials can be used to determine dose and average LET simultaneously. In fast neutron fields they allow neutron and gamma dose to be measured separately. A review is given of the dosimetric properties of different TL materials in therapeutic negative pion, proton, helium, neon and fast neutron fields.