Polyvinyl alcohol (PVA)-based gel dosimeters for radiotherapy: A review

Polyvinyl alcohol (PVA)-based gel dosimeters have attracted sustained interest as three-dimensional (3D) dosimetric materials for external beam radiotherapy because of their water-rich composition, optical readability, and tunable formulation chemistry. However, despite repeated formulation advances, PVA gels remain outside mainstream clinical dosimetry, largely due to persistent challenges related to ferric-ion diffusion, auto-oxidation, formulation-dependent sensitivity, temporal stability, and limited translational standardization. This review critically examines the development of PVA-based gel dosimeters with emphasis on the relationships between formulation chemistry and dosimetric performance. Relevant studies were identified through targeted Google Scholar searches using combinations of keywords related to PVA, gel dosimetry, Fricke dosimeters, iodide-based dosimeters, hydrogel matrices, and radiotherapy dosimetry, followed by reference checking of selected papers. The review focuses primarily on two main PVA-based systems which are Fricke-type formulations and iodide-based formulations. Key formulation variables including polymer concentration, crosslinking strategy, chelating agents, and stabilizing additives are discussed in relation to sensitivity, diffusion control, linearity, dose-rate response, energy dependence and reusability. Rather than treating the performance metrics in isolation, this review highlights the underlying trade-offs that govern practical design, particularly between sensitivity and spatial stability, diffusion control and tissue equivalent water content, and reusability and long-term reproducibility. The review also identifies major limitations of current PVA-based systems, including incomplete suppression of ferric-ion diffusion, residual auto-oxidation, formulation-dependent sensitivity loss, restricted linear dose windows in some chemistries, and trade-offs between spatial stability, optical response, and reusability. Overall, PVA-based gel dosimeters remain a promising but still translationally immature platform for volumetric radiotherapy dosimetry. Future progress will depend on overcoming these intrinsic material and formulation constraints through more effective diffusion control, improved chemical stability, and better preservation of dosimetric performance under clinically relevant irradiation and readout conditions.