The selection of stopping power and mass energy absorption coefficient data for the HPA Code of Practice for dosimetry

All the recent protocols for high-energy X-ray dosimetry, introduced by the AAPM (1983), NACP (1980) and the HPA (1983), result in absorbed dose conversion factors significantly different from those that have been in use since 1969 when ICRU Report 14 was published. Clearly for all protocols, general or specific, it is necessary to select appropriate stopping power and mass absorption coefficient ratios for a range of X-ray beam qualities. Cunningham and Shultz (1984) have recently described a method of selecting these ratios, taking into account differences in spectral properties of radiation beams rather than the peak accelerating voltage which is not an adequate index of radiation quality. A table is given showing quality of X-ray or gamma -ray radiation versus narrow beam attenuation coefficient in water.