Optimization of bromine-based radical initiators using leucomalachite green and solvents in PRESAGE® dosimeter

Abstract

This study has two main objectives. The first objective is to create an ideal dosimeter with improved sensitivity and tissue-like equivalent characteristics. Formulas F1 and F2 were fabricated for this specific purpose. The second objective is to investigate the effect of two bromine-based radical initiators and the effect of adding two types of solvents to PRESAGE® formula on the radiological properties and dose sensitivity of PRESAGE® dosimeter. Formulas F3, F4, F5, F6, and F7 were fabricated for this investigation. In total, seven different PRESAGE® dosimeters containing up to 2 wt% of tetrabromomethane (CBr4) and 1,1,1,2-tetrabromoethane (C2H2Br4) radical initiators were fabricated. They were irradiated with either 250 or 100-kVp X-rays ranging from 0 to 40 Gy. Their optical density changes pre and post irradiation were measured using a spectrophotometer. Besides, radiological properties and sensitivity of PRESAGE® dosimeters were investigated for different percentages of radical initiators and varying amounts of cyclohexanone with a fixed amount of dimethyl sulfoxide (DMSO; 2 wt%). Using Monte Carlo methods, the relative depth doses in water of F2, F3, and F5 were calculated for 50, 100, and 300- kVp X-ray beams and 1.25 MeV from cobalt-60. For all PRESAGE® formulas, an excellent linear correlation between dose response and applied radiation dose was observed. CBr4 showed much higher sensitivity than C2H2Br4 even when using the same weight percentage. The formula F2 exhibited improved sensitivity to radiation than the presented PRESAGE® dosimeter formula named as MOD3, along with radiological properties close to water. The PRESAGE® formula F5 showed a sensitivity increase of 46.1% with addition of DMSO; however, it showed an increase in effective atomic number by ∼1%. The PRESAGE® formula F2 is equivalent to water than formulas F3 and F5 in terms of depth-dose response and can be used in both kilo- and megavoltage beams without correction factors. The PRESAGE® dosimeters with CBr4 as a radical initiator can be used if high sensitivity is required. However, an effective atomic number is not water-equivalent when using a considerable amount of radical initiator (>0.50 wt%).