Proposal for a practical dose calculation scheme for neutron irradiations

Dose calculations for neutron therapy irradiations should be based on the dosimetrically best accessible parameters "total absorbed Dose Dt" and "gamma ray absorbed dose Dgamma". By adequate standardization it should be possible, that only one single reference parameter contains all deviations of calibration, while a table of relative factors, only once to be determined, gives all long-term constant dependencies for all field sizes and phantom depths. A standardization is proposed for the irradiation technique with fixed fields at a constant focus-skin distance, giving rise to especially simple equations for the absorbed doses Dt and Dgamma. It is as well easy to get by these doses and mean relative biological effectivenesses rn for neutrons and rgamma for gamma rays the "total effective absorbed dose De", being an opportune quantity for the biologically weighted absorbed dose. The practical application of equations and tables is demonstrated for an opposing field irradiation as example. Adequately standardized "reference tissue air ratios" and corresponding equations are given for isocentric fixed or rotating beam irradiations and used for the example of a dose calculation within a phantom at the isocentre.