Fricke-infused agarose gel phantoms for NMR dosimetry in boron neutron capturetherapy and proton therapy.

In recent radiotherapy techniques, such as boron neutron capture therapy (BNCT) and proton therapy, the high non-uniformity of the spatial distribution of absorbed dose makes mandatory 3-D dose determinations in order to carry out good treatment planning. The investigated dosimetric technique is based on a chemical dosemeter (ferrous sulphate solution) incorporated in a gel (agarose). Ionising radiation causes a variation in certain parameters of the system such as the relaxation rates of hydrogen nuclei, measurable by nuclear magnetic resonance imaging (NMR) or the gel optical absorption in the visible spectum, measurable by spectrophotometry. Gel containing 10B in the amount typically accumulated in tumours for BNCT was analysed. The isodose curves were obtained from NMR analysis of a phantom of borated gel after irradiation in the thermal column of a nuclear reactor. The results show that the gel is a promising dosimetric system. A method for depth-dose profiling in tissue irradiated by a proton beam is also suggested. In the profile the Bragg peak position has been determined within 0.1 mm and the widening in the peak ramp proves to be about 1 mm.