Dosimetry of beta sources in radiotherapy I. The beta point source dose function

The dose distribution around a point source of a beta-emitting radionuclide in an homogeneous medium is considered. The beta point dose function proposed by Loevinger in 1956 is discussed with respect to the most recent experimental and theoretical available data of Cross and Berger. The Loevinger function provides a reasonable evaluation of the dose distribution at distances of clinical interest. A re-evaluation of the parameters can still improve the situation. A slightly modified formula provides a description of the dose distribution around 32P and 90Y point sources, which is in close agreement, at all relevant distances, with the data of Cross and Berger. This formula can be integrated to provide the dose distribution around beta sources of other shapes.