RADIATION-THERAPY DOSIMETRY USING MAGNETIC-RESONANCE-IMAGING OF POLYMER GELS

Further progress in the development of polymer gel dosimetry using MRI is reported, together with examples of its application to verify trea tment plans for stereotactic radiosurgery and high dose rate brachythe rapy. The dose distribution image produced in the tissue-equivalent ge l by radiation-induced polymerization, and encoded in the spatial dist ribution of the NMR transverse relaxation rates (R(2)) of the water pr otons in the gel, is permanent. Maps of R(2) are constructed from magn etic resonance imaging data and serve as a template for dose maps, whi ch can be used to verify complex dose distributions from external sour ces or brachytherapy applicators. The integrating, three-dimensional, tissue-equivalent characteristics of polymer gels make it possible to obtain dose distributions not readily measured by conventional methods . An improved gel formulation (BANG-2) has a linear dose response that is independent of energy and dose rate for the situations studied to date. There is excellent agreement between the dose distributions pred icted using treatment planning calculations and those measured using t he gel method, and the clinical practical utility of MRI-based polymer gel dosimetry is thereby demonstrated. (C) 1996 American Association of Physicists in Medicine.