Beta and electron dose imaging using a microspectrophotometer system and radiochromic film

Abstract

<p>A dose imaging technique of measuring the distribution of beta particles and high energy electrons, using a microspectrophotometer system and radiochromic film, has been investigated. The investigation entailed the commissioning of the microspectrophotometer and the development of a newly proposed method in film calibration. It was tested successfully by comparing the measured dose, determined using the calibration method, of films irradiated by a 32 P source, and the expected dose, determined by beta counting based on the equilibrium geometry with dose loss correction to the film substrate (20%). This method was also demonstrated to extend the usable dose range of the film. The dose imaging technique was applied to two experiments. The first experiment examines the beta depth dose distribution in Lucite, irradiated by a 32 P volume source. The experimental results were compared to Monte Carlo simulation, performed using the ITS code. The experimental distributions were found to agree closely with the Monte Carlo values up to a depth of 3 mm, but were significantly higher beyond. The second experiment examines the electron dose distribution in Lucite, irradiated by a narrow 10 MeV electron beam. The lateral experimental dose distributions were found to agree well, except at the tail end, with Monte Carlo values up to about 20 mm depth. Elsewhere, the experimental dose was found to be higher. The disagreement with Monte Carlo simulations at low doses in both experiments perhaps indicates a real discrepancy; further experimental investigations are required. The lateral spread of the beam was also investigated by determining the linear scattering power. The experimental values of the linear scattering power were found to be smaller than those quoted in the ICRU report 35 by a factor of 1.8 or less.</p>