Many High Dose Rate treatment planning systems that are in use fail to correct for heterogeneities. If the treatment planning system does not correct for heterogeneities, it would assume that the patient is receiving full scatter when in reality, the patient will possibly be underdosed. A 1cm diameter planning target volume for a lumpectomy cavity could extend beyond the skin or chest wall for the patient and could be a great problem when it comes to treatment with the MammoSite® single lumen breast applicator. A previous Monte Carlo study tested 3 MammoSite® balloon sizes at various depths beyond the planning target volume to see how much tissue would be needed to achieve full scatter. The results showed that on average, if there was no tissue beyond the prescription line of 1cm there would be a 10% dose reduction for the breast – skin interface.
The purpose of this study is to use the Strut Adjusted Volume Implant (SAVI) multi-lumen breast applicator to re-create the measurements done with the MammoSite® balloon and expand these measurements to include tissue thicknesses less than the PTV. Previous simulations with the MammoSite® were done using Monte Carlo, with tissue thicknesses beyond the planning target volume of 0 – 10cm. This study will re-create these measurements using Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) and also take measurements below the prescription line of 1cm due to the ability of the SAVI applicator to adjust dose to the skin.