Dosimetry of the Varian Clinac-4 linear accelerator. I. Basic radiation parameters.

Four-megavolt x rays were measured to determine central axis depth-dose data for 100 cm TSD; TMR at 80 and 100 cm target-axis distance; depth of maximum dose; field-size dependence; and half-value thicknesses of water, Lucite, and Alderson tissue-equivalent material. Sable's 80 cm depth dose data were verified. Maximum dose in water varies from 1.1 to 1.3 cm; integrated dose at 1.2 cm varied from 0.94-1.09, relative to a 10 X 10 cm field. TMR and per cent depth dose were tabulated for brass and lead flatness filters, providing basic data for fixed-field and rotational dosimetry.