Magnetic-Resonance-Imaging based Polymer Gel Dosimetry: Methodology, Spatial Resolution, Applications

Modern radiation techniques aim on improved 3-dimensional (3D) spatial selectivity of the dose application sparing dose from organs-at-risk (e.g. IMRT with micro-multileaf collimation, γ-knife-, Brachyand heavy-ion therapy). The corresponding 3D-dose distributions exhibit high dose gradients above 4 Gy/mm, which are difficult to be investigated using standard single-point dosimetric detectors as ionization chambers, which cover a minimum size of few mm. Parameter selective Magnetic Resonance (MR) based dosimetry (MRPD) represents a 3D detection method, capable of high spatial resolution. Moreover tissue equivalence of the detector material (a polymer-gel) is offered. This review is focused on polymer-gels using the polymerization of monomers during ionizing radiation. The change in the mobility of the detected molecules is detected via parameter-selective (T2) MR-imaging. A manufacturing recipe for the actually used “normoxic” polymer gels, which allow simple processing at normal oxygen pressure in atmosphere, is listed. Data on sensitivity, precision, accuracy, spatial resolution and sensitivity to different radiation quality (i.e. energy, particle type) is presented. Dosimetric images for two highly-spatially selective radiation applications (i.e. a 2 mm electron-beam and a mixed 11 mm γ-knife collimation) from our lab demonstrate the capabilities of high-resolution MRPD at voxel size of 0,2 x 0,2 x 1 mm. Finally limitations of MRPD for actual clinical applications are discussed. Keywords— Dosimetry, MRI, Polymer, Gel, Review