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Bolusing Effect of Fiberglass Casting Material for 6MV Photon Beam Treatments Measured with Parallel Plate and Gafchhomic Film

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


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Patients are arriving in the department with other co-morbidities including fractured bones, heart issues, and stents. This study was designed to measure the bolusing effect of standard casting material for setting fractured appendages

Fiberglass casting material in thicknesses of 1mm were cast, and allowed to cure overnight. CT scans were obtained for different thicknesses of material positioned on a solid water phantom. Using the Varian Eclipse planning system, and the ACUROS dose algorithm, plans for the different thicknesses of cast were developed.
A Parallel-Plate chamber was positioned in a solid water phantom on a Varian Truebeam accelerator table. All Measurements were made with a 10x10 field size, 6MV beam, and different thicknesses of material on the solid water phantom. The same setup was used with solid water.
Using the same setup geometry gaf-chromic film was used in place of the Parallel Plate chamber. The results were then compared to the Parallel Plate results.
A second setup was conducted with the casting material and the cotton padding used with the cast. The same measurements were repeated with the cotton and casting material in place.

The measured surface dose for the 6MV beam was 48.4%. The addition of the cotton padding increased the surface dose to 63%. One layer of casting material increases the dose by 15%. Four layers of casting material increases the measured dose to 73%, which is equivalent to 2mm of solid water. Ten layers increased the dose to 90%, and is equivalent to 5mm of solid water. The addition of the cotton padding increased the bolusing effect by 3%.

The fiberglass casting material does cause a significant blousing effect of the delivered dose. Two layers of fiberglass casting is equivalent to 1mm of solid water throughout the buildup region for a 6MV photon beam.


Radiochromic Film, Surface Dose, Treatment Techniques


TH- External Beam- Photons: General (most aspects)

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