RESPONSE ANALYSIS OF TLD-300 DOSIMETERS IN HEAVY-PARTICLE BEAMS

In vivo dosimetry is recommended as part of the quality control proced ure for treatment verification in radiation therapy. Using thermolumin escence, such controls are planned in the p(65)+Be neutron and 85 MeV proton beams produced at the cyclotron at Louvain-La-Neuve and dedicat ed to therapy applications. A preliminary study of the peak 3 (150 deg rees C) and peak 5 (250 degrees C) response of CaF2:Tm (TLD-300) to ne utron and proton beams aimed to analyse the effect of different radiat ion qualities on the dosimetric behaviour of the detector irradiated i n phantom. To broaden the range of investigation, the study was extend ed to an experimental C-12 heavy ion beam (95 MeV/nucleon). The peak 3 and 5 sensitivities in the neutron beam, compared to Co-60, varied li ttle with depth. A major change of peak 5 sensitivity was observed for samples positioned under five leaves of the multi-leaf collimator. Wh ile peak 3 sensitivity was constant with depth in the unmodulated prot on beam, peak 5 sensitivity increased by 15%. Near the Bragg peak, pea k 3 showed the highest decrease of sensitivity. In the modulated proto n beam, the sensitivity values were not significantly smaller than tho se measured in the unmodulated beam far from the Bragg peak region. Th e ratio of the heights of peak 3 and peak 5 decreased by 70% from the Co-60 reference radiation to the C-12 heavy-ion beam. This parameter w as strongly correlated with the change of radiation quality.