Three-dimensional optical tomography of dose distribution using radiation sensitive transparent gels

The ability to determine the absorbed dose distribution in tissue is essential for radiotherapy planning. A three-dimensional optical tomography system used to map dose distribution and the radiation sensitive transparent gel (Ferrous sulphate Xylenol orange in Gelatin gel) used are described. The system is capable of collecting two-dimensional projections and hence able to reconstruct three-dimensional dose maps. The equipment used is inexpensive and readily available offering an alternative to the magnetic resonance imaging of three-dimensional dose distributions. The FXG gel used undergoes the greatest change in optical density at 590nm (the wavelength produced by a sodium lamp) when exposed to an ionising radiation. We have shown the change in optical density is directly proportional to the absorbed dose up to 20Gy. A three-dimensional dose map imaged by the system shows the expected cone-beam of dose produced by a 50kVp silver anode X-ray tube.