Proton response of alanine based pellets and films

The performance of two different alanine-ESR systems (1 mm ISS pellets and NRI films) in therapy proton beams was checked against reference dosimetry provided by a Markus parallel plate ionization chamber. Irradiations were performed at the OPTIS facility of the PSI with a 62 MeV proton beam. The energy dependence of the response was derived from the analysis of film stacks irradiated with pristine beams. In fact, 250 μm films allowed for a high resolution sampling of the proton slowing down mechanisms. Moreover pellets were irradiated in unmodulated and modulated beams. Alanine dose distributions were always in good agreement with the PSI Markus chamber results. Simple density scaling allowed for the conversion of the results to the dose distributions in water, consistently with the good tissue equivalence properties of these detectors. (Author)