Brachytherapy dosimetry with fricke-gelatin and MRI

Magnetic Resonance Imaging (MRI) and Fricke-gelatin dosimetry are used to measure absorbed dose distributions from high dose rate (HDR) brachytherapy treatments. The high activity of the HDR brachytherapy source is suitable for the prompt delivery of the high doses required to give changes in the Fricke-gelatin Nuclear Magnetic Resonance (NMR) characteristics which are readily detected by MRI. The MR images can map 3D dose distributions deposited in the Fricke-gelatin matrix. Spin-lattice relaxation times (T1) and rates (R1) are computed from MR images of irradiated Fricke gelatin phantoms in order to study the dose response relationship for the Fricke gelatin system. It was confirmed that the Fricke gelatin system's R1 varies linearly with absorbed dose to a saturation limit. A fast approach for determining radiation dose from MR image intensity using a calibration curve is described. Dose distributions generated from MR images via the calibration curve show good agreement with expected distributions generated from a computerized treatment plan. As well, dose data generated using R1 maps agreed well with those generated by calibration curve. The use of MRI with Fricke-gel dosimetry is shown to be a viable means of verifying the dose distributions from high activity brachytherapy sources