BANG™ polymer gels applied to the verification of conformal heavy ion radiotherapy

Abstract

Magnetic Resonance Imaging (MRI) can be used to measure the dose distribution produced by sparsely ionizing radiation absorbed in tissue-equivalent BANG™ polymer gels [1, 2]. In contrast to conventional dosimetry techniques using ionization chambers or thermoluminescence detectors (TLD) MR imaging of BANG™ gels allows the verification of complete three-dimensional dose distributions with one single measurement. It is not obvious, that this technique can immediately be extended to densely ionizing radiation like the ¹²C⁶⁺ beam used in the radiotherapy project started at the Gesellschaft für Schwerionenforschung mbH (GSI), Darmstadt, Germany. For such high-LET radiation saturation effects can be expected, just like for any other condensed phase detector. Another difficulty arises from the fact that a ¹²C beam in matter undergoes fragmentation and generates a mixed radiation field of various particles with different energies. Contributions of different particles with a spectrum of energies generate the signal in the detector and this is not necessarily identical to the physical dose .