THE SOURCE-DENSITY FUNCTION - DETERMINATION FROM MEASURED LATERAL DOSE DISTRIBUTIONS AND USE FOR CONVOLUTION DOSIMETRY

A method for determination of the spatial intensity distribution (sour ce-density function) of the photon source of a teletherapy unit is pre sented. It is designed to be consistent with convolution methods for p hoton dose calculations and consists of the deconvolution of measured lateral dose distributions using Monte Carlo-generated pencil-beam ker nels and obtaining the inverse Abel transform of the first derivative of the properly scaled primary fluence profiles. The method has been a pplied for two linear accelerators, a Co-60 source and a neutron gener ator. The use of the source-density function for convolution dosimetry is demonstrated and calculated dose profiles and output factors of st ereotactic collimators are compared with measurements. The accuracy fo und in dose profiles is better than 0.25 mm and in output factor it is better than 2%.