Preliminary investigation of iodine-doped MR-based polymer gel dosimeter for fiducial-free tumour-tracking radiotherapy.

Abstract

PurposeThis study aims to utilise an iodine-doped magnetic resonance (MR)-based polymer gel dosimeter to achieve three-dimensional (3D) dose-distribution measurement combined with accurate target visualisation under kilovoltage (kV) X-ray imaging and fiducial-free tumour-tracking radiotherapy.MethodsThe structural information required for dynamic tracking was incorporated by embedding a 2 wt% iodine-containing contrast agent into designated target regions of a normoxic N-vinylpyrrolidone-based polymer gel dosimeter. The gel dosimeter was irradiated using the Synchrony® motion tracking system on a Radixact® system (Accuray, Inc., USA) under three experimental conditions: (1) tracking during motion, (2) no tracking during motion, and (3) no tracking under stationary (no-motion) conditions. The resulting dose distributions were compared with treatment planning system (TPS) calculations.ResultsThe iodine-doped gel dosimeter exhibited a linear dose response, confirming that iodine addition did not significantly alter dose sensitivity. The target region enhanced with the 2 wt% iodine-containing contrast agent was clearly visualised in kV X-ray images, enabling accurate tracking without gold or other fiducial markers. The 3D dose distribution under the tracked condition showed high agreement with the TPS calculations (gamma pass rate: 94.7%).ConclusionsThe iodine-doped region within the polymer gel dosimeter functions as a tracking marker while simultaneously enabling 3D dose measurement. These results demonstrate the feasibility of using iodine-doped polymer gel dosimeters to evaluate dynamic tumour tracking and dose distribution in fiducial-free radiotherapy.