Dosimetry close to an Ir-192 HDR source using N-vinylpyrrolidone based polymer gels and magnetic resonance imaging

In this work, the utilization of polymer gel-MRI dosimetry for measurements at distances relevant to clinical brachytherapy and intravascular applicat ions [i.e., in the mm range, where steep three-dimensional (3-D) dose gradi ents exist] is investigated using N-vinylpyrrolidone-based gels. Transverse axis radial dose distributions, dose distributions parallel to the source axis, and 2-D dose distributions around the commonly used microSelectron Ir -192 HDR source are measured for single source dwell position irradiations. Experimental results are found in good agreement with verified Monte Carlo calculations, even for distances less than 3 mm from the source. The effec t of various MRI parameters, such as slice thickness, slice mispositioning, and in-plane resolution, on the accuracy of the method is also investigate d. Possible limitations of the method are discussed, and its' overall poten tial in brachytherapy dosimetry is evaluated. Experimental 2-D dose distrib utions for an intravascular application following the Paris irradiation pro tocol are compared to corresponding commercial treatment planning system ca lculations. Results suggest that polymer gel-MRI dosimetry is capable of ex perimentally verifying dose distributions in relevant clinical intravascula r applications. (C) 2001 American Association of Physicists in Medicine.