Calculation and application of point spread functions for treatment planning with high energy photon beams

A general dose calculation method for treatment planning with high energy photon beams, based on folding of the total energy released by primary photons per unit mass, the terma, with a fractional mean energy imparted point spread function is described. A set of point spread functions has been calculated with Monte Carlo technique for energies of primary photons between 100 keV and 20 MeV. Dose distributions have been calculated for a 6 MV bean using the method. The results clearly point out the considerably increased precision and flexibility achieved when calculating photon beam dose distributions from first principles using Monte Carlo generated point spread functions. The point spread functions calculated in this work are available on magnetic tape from the authors.