Room: Exhibit Hall | Forum 4
Purpose: Under most cell and small animal irradiations, the backscatter material present is often insufficient for full backscatter condition. TG61 and other dosimetry protocols lack guidance in dosimetry under those conditions. The purpose of this study is to characterize and measure this effect.
Methods: MC models for Precision X-RAD irradiators were built with PENELOPE based on the X-ray spectra provided by the manufacturer. Depth doses under different thickness water phantom were simulated. Absolute film dosimetry was established. Both ion chamber and EBT3 films were used to measure the dose under insufficient backscatter conditions. The MC model was applied to an actual cell irradiation experiment. MC simulated dose was compared with film measurements.
Results: Monte Carlo simulation showed that as much as 50% dose difference exists for different backscatter conditions at the orthovoltage energy studied. Ion chamber and film measurement in solid water blocks agreed with simulation to within 2%. On more complex geometry, film measured cell experiment dose agrees with the simulation to within 5%.
Conclusion: Backscatter conditions at orthovoltage energy greatly influence the dosimetry. Care must be taken to either ensure the full backscatter condition, or to account the effects accurately.