Improvement of linear accelerator depth-dose curves.

A semiempirical analytic description of the accelerator depth-dose curve is described along with its physical explanation. The results of Monte Carlo calculations are presented and compared with experimental data to test this model. Calculations were made for different atomic number (Z) materials used as x-ray targets and flatteners, with the results showing that medium-Z materials are the logical choice. It is demonstrated empirically that Dmax is a simple function of the average energy (E) of the x-ray spectrum. The variation of E with Z of the target and flattener is demonstrated. As a practical example, Monte Carlo calculations and experimental data for old and new Clinac 35 accelerators are presented.