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Dose Distribution in the Near Zone of a CO2 Filled Breast Expander for 6MV and 10MV Photon Beams

B Hasson1*, T Li2 , C Geraghty3 , J Carroll4 , M Young4 ,(1) Anne Arundel Medical Center, Annapolis, MD, (2) ,Annapolis, MD, (3) Anne Arundel Medical Center, Annapolis, MD, (4) Versant Medical Physics & Radiation Safety, Tewksbury, MA, (5) Anne Arundel Medical Center, Annapolis, MD,


(Monday, 7/15/2019) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 3

Purpose: This study focused on the dose in-homogeneity in target tissues surrounding a CO2 filled breast expander. The dose at varying depths of tissue were measured for 6MV and 10MV photon beams.

Methods: An 800cc expander from Aeroform was inflated to maximum capacity as 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 planning. Plans were generated with a bolus thickness of 1.6cm overlaying the expander. Dose was calculated Acuros XB algorithms v13.7. Bolus was added during the planning stage to simulate overlying breast tissue. Tangential beams were created, and an isocentric plan developed. Plans were calculated and delivered with 6MV, and 10MV photon beams. During plan delivery measurements were done with gafchromic EBT3 film, and OSLDs positioned on and off-axis of the field. The measuring devices were placed at the interface of the expander and bolus, 3mm, and 6mm from the interface. Gafchromic films were scanned with an Epson 12000 scanner, and analyzed with RIT software.

Results: OSLD and gafchromic film measurements were within 5% of the Eclipse treatment planning calculations at 3mm, and 6mm depth. Acuros calculated doses and measured results were within 10% at the bolus surface for both 6MV and 10MV beams. The overall dose uniformity throughout the bolus surrounding the expander was approximately 10%.

Conclusion: Measurements confirmed the relative dose homogeneity within the tissue rind surrounding the Aeroform cavity for both energies. The Aeroform expander does perturb the dose distribution when compared to a homogenous material. However, the Eclipse Acuros XB algorithm 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 Acuros XB algorithm.


Dose Uniformity, Breast, Inhomogeneity Corrections


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

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