Room: Exhibit Hall | Forum 7
Purpose: The AeroForm breast implant is a silicone enclosed gas filled expander containing a carbon dioxide reservoir made of metal. The tissue-gas-metal interface poses challenges for radiotherapy planning and dosimetry as compared to traditional saline filled expanders. This work evaluated the accuracy of dose calculations and tested the feasibility of a planning technique with the AeroForm expander.
Methods: To evaluate the dosimetric accuracy, an in-house phantom was created and three plans were delivered to the phantom: 6MV VMAT with partial arcs, 6MV tangents, and 10MV tangents. All components of the expander and metal artifacts were contoured and overwritten to true densities. TLDs were placed at six locations on the surface of the expander. The measured doses were compared with the Adaptive Convolve calculated doses. To test the planning technique with the existence of high heterogeneity, plans were created for a patient with the AeroForm expanders using photon four fields and VMAT with the PTV including the left reconstructed chest wall, supraclavicular nodes, axilla, and internal mammary nodes.
Results: TLD measured doses are higher than planned by 9.8%, 14.6%, and 15.0% at the metal reservoir, and in average by 4.4%, 7.1% and 3.5% for the remaining five locations for the VMAT, 6MV tangential, and 10MV tangential phantom plans, respectively. Among the test plans, only the VMAT plan was clinically acceptable, with 90.71% of the PTV receiving the prescription dose, maximum dose of 53.80Gy, mean heart dose of 4.16Gy, and whole lung V20Gy of 13.17%.
Conclusion: With the AeroForm breast implant, measured doses are higher at the phantom-gas-metal interface possibly due to decreased attenuation by the gas and increased scatter by the metal. VMAT is a feasible planning technique to compensate for heterogeneity inside the target volume, though this does represent a change from our standard 3D-CRT technique with saline filled expanders.
Funding Support, Disclosures, and Conflict of Interest: M Svatos is a consulting medical physicist to AirXpanders, the manufacturer of the AeroForm tissue expander.