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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

Presentations

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

Room: AAPM ePoster Library

Purpose:
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

Methods:
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.


Results:
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%.

Conclusion:
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.

Download ePoster [PDF]

Keywords

Radiochromic Film, Surface Dose, Treatment Techniques

Taxonomy

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

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