The effect of stopping power ratios of different protocols on %DD curve

OBJECTIVES: The effects of the stopping power ratios of different protocols on %DD curve were investigated in this study. METHODS: Percentage ionization curve was measured at SSD=95 cm using 10x10 standard cone and 6, 8, 10, 12, 15 and 18 MeV electron energies. Stopping power ratios at each depth were determined as recommended by the three protocols. %DD curves were then found and compared. The stopping power ratios of the different protocols were determined and plotted against R50. RESULTS: The stopping power ratios of the different protocols did have an effect on %DD curves. The clearest difference was seen at the surface. The maximum difference was 1.45% at 10 MeV, while the minimum difference was 0.09% at 6 MeV. CONCLUSION: Stopping power ratios as found using realistic electron beams provide more accurate surface doses, as reported in the literature.