We have produced an optically clear, close to water-equivalent gel that is radio-fluorogenic, i.e. fluoresces in UV light after exposure to high-energy radiation. Its potential as a 2D and 3D dosimetric medium is demonstrated by fixed fluorescent images of the cross-section, track and intersection of collimated (10 × 10 or 5 × 5 mm(2)) 205 kVp x-ray beams. The images, produced by doses on the order of 10 Gy, are formed instantaneously and can be digitally recorded and scanned with a spatial resolution on the order of 0.1 mm. No loss of spatial resolution occurs on standing under ambient conditions for at least 3 days.