Author: Jordan B Lunsford, Sagar Pokhrel, Ashkan Shafiee, Curtis S. Whiddon 👨🔬
Affiliation: Atrium Health Wake Forest Baptist, University of North Carolina, Atrium Health Wake Forest Baptist High Point Medical Center 🌍
Purpose: To investigate the dosimetric characteristics of a platinum cured silicone rubber material (Platsil) for use as custom bolus in radiotherapy
Methods: Sheets of 2, 4, 6, and 8 mm Platsil were fabricated. Stacking allowed for additional thicknesses of 10, 16, and 20 mm. 6 and 10 MV photons percent depth dose (PDD) in the buildup region was measured using a PTW Markus parallel-plate detector in a solid water phantom, 10x10cm2 field size, 100 cm SSD, and varying thicknesses of Platsil, Superflab, and solid water. Transmission measurements at dmax for solid water and Platsil were used to calculate the solid water equivalent thickness of Platsil. Uniformity was measured for the Platsil sheets at one central and four peripheral locations at the surface and dmax using 6 MV photons and 3x3 cm2 field size.
Results: Platsil provides similar dose increases in the buildup region as solid water and superflab. For 6 MV photons, surface dose increased from 13.6% with no buildup to 96.6%, 98.3%, and 100.2% for 1 cm of Platsil, Superflab, and solid water respectfully. For 10 MV photons, surface dose increased from 11.2% with no buildup to 93.1%, 91.4%, and 91.7% respectively. 1 cm of solid water is equivalent to 0.91 cm of platsil. Uniformity was within 1.5% for all Platsil thicknesses except 2 mm where the maximum difference was 4.7%.
Conclusion: Platsil is a commercially available silicone rubber material that can be mixed and poured into various shapes and has potential as custom bolus material in radiation therapy. Our results indicate that although Platsil is slightly more attenuating than solid water, the effect on PDD in the buildup region is similar for Platsil, solid water, and Superflab. Uniformity measurements show that the fabrication process results in consistent density which is desirable for custom bolus material.