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Dose Perturbation of the Metallic Reservoir From a Novel Tissue Expander Used for Post Mastectomy Radiation Therapy

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


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: The Aeroform tissue expander has a gas filled metallic reservoir assembly inside. Due to its high density, the current dose calculation algorithms may not model all photon interactions (such as, pair production) accurately. As a first step, in this study, we measured and evaluated the dose perturbation by the metallic reservoir using EBT3 Gafchromic film.

Methods: The metallic reservoir was removed from a small (400 cc) Aeroform tissue expander device. Sheets of EBT3 film were placed directly under and immediate to the right side of the metallic reservoir. The metallic reservoir along with the films were irradiated to 900 monitor units with a 10 cm × 10 cm field at gantry angle of 90 degree using 6-MV photons. Other films were again placed under the metallic reservoir, 900 MU was delivered using 6 MV photon beam, 10 × 10 field size with gantry at 0 degree. The films were scanned with flatbed scanner (Epson Expression 12000 XL) and imported into RIT software for analysis.

Results: Dose enhancement over 20% was observed surrounding the metallic reservoir. This dose enhancement extended to a distance of approximately 4 mm in EBT3 film (density 1.4 g/cm3). The estimated maximum electron energy is below 600 keV. The range of electron with this energy is approximately 5 mm to 6 mm in Silicone (density 1.02 to 1.07 g/ cm3), and 5.3 mm to 6.3 mm in water. Also on irradiated films, well-defined, cone-shaped under dose region (approximately 15%) was observed at the distal end of the metallic reservoir when the beam was parallel.

Conclusion: Due to increased probability of secondary electron generation, the metallic reservoir will have significant perturbation on the dose distribution throughout the Aeroform tissue expander. The clinical impact of these perturbations on radiation treatment planning and delivery warrant further evaluation.


Dose, Film, Radiation Dosimetry


TH- External beam- photons: Standard field experimental dosimetry

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