Dosimetric Effects of Intrafractional Target Motion Using the Xiphiod Process as a Surrogate During Deep Inspiration Breath Hold for Left-Sided Breast Cancer

Abstract

above the chamber for adjusting the mean electron energy incident on the lead solid-water interface. Such measurements were repeated with the removal of lead sheet. By comparing the measured dose with and without the lead sheet, the backscatter effect of electrons from the lead interface could be derived experimentally at different depths away from the lead interface. To investigate the impact of lead heterogeneity in the eMC calculation, metallic artefact-free MVCTs were done on all setups used in previous dose measurements. and imported into the planning system for eMC dose calculations. Finally, the impact on the accuracy of the eMC algorithm due to backscatter effect from lead heterogeneity can be found by comparing the measured and calculated dose in different setups. Results: At the lead-solid water interface (depth Z 0 cm), the eMC calculation underestimated the dose in the range between 61.5 AE 4.4% to 47.5 AE 3.3% for the mean energy of the electron incident on the interface ranging from 2 to 11 MeV. Such underestimation was reduced to between 12 AE 0.8% and 14.5 AE 0.9% at the depth 1 cm away from the interface. It was further reduced to between 5.6 AE 0.4% and 8.5AE 0.6 % at the depth 1.5 cm away from the interface. Conclusion: When there is a presence of lead heterogeneity in an electron beam, eMC dose calculation underestimates the dose depending on treatment depth. Special attention must be paid in the eMC plan when lead is used as an inner shield.