FRICKE-INFUSED AGAROSE-GEL PHANTOMS FOR NMR DOSIMETRY IN BORON NEUTRON-CAPTURE THERAPY AND PROTON THERAPY

In recent radiotherapy techniques, such as boron neutron capture thera py (BNCT) and proton therapy, the high nonuniformity of the spatial di stribution of absorbed dose makes mandatory 3-D dose determinations in order to carry out good treatment planning. The investigated dosimetr ic technique is based on a chemical dosemeter (ferrous sulphate soluti on) incorporated in a gel (agarose). Ionising radiation causes a varia tion 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 spectrum, measurable by spectrophotometry. Gel containing B-10 in the amount typically acc umulated in tumours for BNCT was analysed. The isodose curves were obt ained from NMR analysis of a phantom of berated 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 profilin g in tissue irradiated by a proton beam is also suggested. In the prof ile the Bragg peak position has been determined within 0.1 mm and the widening in the peak ramp proves to be about 1 mm.