A simplified approach to beta dosimetry for small spheres labelled on the surface

The authors studied source spheres of radii 5 μm-5mm surface labelled with beta emitters to simulate conditions of radioimmunotherapy for small tumours. They calculated, for different source sizes, the absorbed fraction of emitted energy and mean dose rate in smaller concentric spherical targets simulating cell nuclei. A different approach allowed for calculation of dose rate as a function of distance from the centre of the radiolabelled source sphere. Calculations were performed for monoenergetic emissions, which were then integrated over the beta spectra of various emitters (177Lu, 67Cu, 186Re, 111Ag, 131I, 153Sm, 90Y and 188Re). For spheres with dimensions that are small compared to the mean particle range, the mean dose rate could be a misleading parameter since there is a large variation in dose rate with the distance to the source. Results agree well with different analytic approaches reported but differ from those obtained using a Monte Carlo code. (author)