Measurement of Radial Dose Distributions Around Small Beta Particle Emitters Using High Resolution Radiochromic Foil Dosimetry

A method is described for the direct measurement of the radial dose distributions around small (from several mm down to tens of µm in diameter) beta particle emitters. The method employs the high resolution readout of radiochromic dye foils. These foils form a blue image upon irradiation and require no processing to stabilise the image. The colour change (in units of absorbance) is nearly linear with absorbed dose over a range of 10Gy to 1000 Gy and the response to electrons is nearly identical to 60Co gamma radiation which makes the system easy to calibrate. Readout is performed with a laser scanning densitometer with a 100 µm spot size which can be stepped in increments of 40 µm in two dimensions. Examples of the results of measurements of 90Sr/90Y eye applicators as well as particle sources of 90Sr/90Y, 60Co, and 170Tm are given.