[BANG-polymer dosimetry in the proton therapy of eye neoplasms]

The use of polymer gel makes it possible to measure three-dimensional dose distributions of ionizing radiation. Phantoms with BANG-1 and BANG-3 gel were irradiated using a 68 MeV proton beam at the eye tumour therapy beam line of the Hahn Meitner Institute in Berlin. Up to twelve treatment fields could be applied to one gel phantom. The investigations consisted of mono-energetic Bragg curves, spread-out Bragg curves of circular fields (diameter 20 mm), and spread-out Bragg curves of patient fields. Magnetic resonance imaging was used to obtain the gel dose distributions. The results were compared to measurements of a water-phantom ionization chamber. The BANG polymer gels showed a significant quenching of Bragg peaks compared to ionization chamber measurements. The BANG-3 gel was found to be unsuitable for further investigations with 68 MeV protons. The use of BANG-1 allowed the verification of wedge slopes and irregular field forms. On the basis of our experience, polymer gels are well suited for quality assurance in proton therapy in principle.