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  4. Comparison of Measured and Calculated Doses in the Tissue Surrounding a CO2-Filled Breast Expander

Comparison of Measured and Calculated Doses in the Tissue Surrounding a CO2-Filled Breast Expander

C Geraghty*, B Hasson , T Li , Anne Arundel Medical Center, Annapolis, MD

Presentations

(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: This study focused on the dose inhomogeneity in target tissues surrounding a CO2 containing breast expander. To address these concerns, the dose distribution near the tissue expander for different thicknesses of surface material was measured and compared to treatment planning results.

Methods: An 800cc expander from Aeroform was inflated to maximum capacity per manufacturer’s recommendations. The expander was positioned on a 10cm thick plastic water base. CT scans were acquired, and the images networked to the Eclipse TPS. Plans were generated with bolus thicknesses of 0.6cm and 1.5cm overlaying the expander and with AAA and Acuros XB algorithms v13.7. The Bolus was added to simulate overlying breast tissue. Tangential 6MV beams were created, and an isocentric plan developed. Plans were calculated with AAA and Acuros and delivered with gafchromic EBT3 film and OSLDs positioned on and off-axis of the field. The measuring devices were placed at the air/tissue surface and at depths of 3mm and 6mm. Gafchromic films were scanned with an Epson 12000 scanner, and analyzed with RIT software.

Results: OSLD and gafchromic film measurements with 0.6cm bolus were within 10-15% of the Eclipse treatment planning calculations at 3mm and 6mm depth anterior of the CO2 cartridge. AAA and Acuros doses differed by up to 22% at the bolus surface. Acuros showed larger dose heterogeneity within the CO2 cavity of the Aeroform device compared to AAA.

Conclusion: Measurements confirmed the relative dose homogeneity within the tissue rind surrounding the Aeroform cavity. The Aeroform expander does perturb the dose distribution when compared to a homogenous material. However, the Eclipse TPS calculated the dose distribution accurately when compared to measured doses. The very complex dose geometry, and the low and high density interfaces of the device are well accounted for with the Eclipse treatment planning system.

Keywords

Breast, Treatment Planning

Taxonomy

TH- External beam- photons: treatment planning/virtual clinical studies

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