A study on properties of water substitute solid phantom using EGS code

Abstract

To reduce the uncertainty in the calibration of radiation beams, absorbed dose to water for high energy electrons is recommended as the standards and reference absorbed dose by AAPM Report no. 51, IAEA Technical Reports no. 398 and JSMP Standard dosimetry for radiotherapy 2001. In these recommendations, water is defined as the reference medium, however, the water substitute solid phantoms are discouraged. Nevertheless, when accurate chamber positioning in water is not possible, or when no waterproof chamber is available, their use is permitted at beam qualities R(sub 50) less than 4 g/cm(exp 2) (E(sub 0) less than 10 MeV). For the electron dosimetry using solid phantom, a depth-scaling factor is used for the conversion of depth in solid phantoms to depth in water, and a fluence-scaling factor is used for the conversion of ionization chamber reading in plastic phantom to reading in water. In this work, the properties, especially depth-scaling factors c(sub pl) and fluence-scaling factors h(sub pl) of several commercially available water substitute solid phantoms were determined using EGS Monte Carlo simulation. Furthermore, the electron dosimetry using these scaling method was evaluated. As a result, it is obviously that dose-distribution in solid phantom can be converted to appropriate dose-distribution in water by means of IAEA depth-scaling.