Three-dimensional dose distribution around air and bone in tissue measured by mri-based polymer gel dosimeter

Abstract

Heterogeneity correction in dose calculation is necessary for radiation therapy treatment plans. Dosimetric measurements of the effects are hampered if the detectors are large and their radiological characteristics are not equivalent to water. Gel dosimetry can solve these problems. Furthermore, it provides detailed three-dimensional (3D) dose distributions. We used a cylindrical phantom filled with BANG-3 polymer gel to measure 3D dose distributions in inhomogeneous media. The phantom has a cavity, in which water-equivalent or bone-equivalent solid blocks can be inserted. The irradiated phantom was scanned with an MRI scanner. Dose distributions were obtained by calibrating the gel for a relationship between the absorbed dose and the spin-spin relaxation rate. We observed 3D dosimetric structures around the heterogeneity. The dose distributions were unique to the photon energy (6MV or 18MV), the field size and the type of heterogeneity material (air or bone).