An expression for backscatter factors for orthovoltage x-rays

Backscatter factors for orthovoltage x-ray beams are fitted with the expression BSF = 1 + ms/(s + n), where s is field size and m and n are adjustable parameters. The accuracy is better than 0.5%. Good results were also obtained for Cs-137 gamma rays at depth 0.12 cm and Co-60 gamma rays at depth 0.5 cm using the same expression, which failed, however, for peak scatter factors at high x-ray energies.