Gel dosimeters have the potential to measure radiation dose in 3D, allowing for improved treatment planning in radiotherapy. Despite extensive research over the last three decades, gel dosimeters have yet to achieve widespread clinical acceptance. The major limitation is the spatial instability of dose information, caused by diffusion of the small molecule radiographic components within the gel matrix. To overcome the issue of diffusion we propose a new approach to designing Fricke gel dosimeters, where the radiographic component, xylenol orange (XO), is chemically conjugated to the polymer matrix prior to gel formulation. We introduce the synthesis of a novel alkyne-functionalised xylenol orange chelate and the chemical conjugation to azide modified poly(vinyl alcohol) through copper catalysed azide-alkyne click chemistry. Dosimeters composed of the novel PVA-bound XO, even with a low concentration of XO (0.1 mM), show good contrast between irradiated and non-irradiated voxels. Critically, they show no loss of dose information and limited blurring in optical CT imaging, even 18 h post-irradiation, as the diffusion of the Fe(III)-XO chelates is prevented.