J Cui*, J Cui, J Cui, Z Xu, C Cheng, I Mustaphalli, F Momin, W Yang, H Gallogly, S Bian, O Ragab, L Ma, University of Southern California, Los Angeles, CA

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  J Cui

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TU-D930-IePD-F4-3 (Tuesday, 7/12/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 4

Purpose: To quantify the attenuation and bolusing effects of brass mesh and its application for postmastectomy chest wall (CW) and groin area irradiation where conventional bolus is air-gap prone.

Methods: Brass mesh is 1.5-mm thick brass with high temperature enamel. The attenuation of brass mesh was quantified. To mimic CW tangential fields, two lateral beams of 100 MU each (6MV and 6FFF) were delivered on an ArcCHECK phantom. MOSFETs were used to measure surface dose at four locations, 0°(medial), 15°, 30°, and 45° and underneath thermoplastic breast support, thermoplastic sheet, brass mesh, and with 1-cm air gap. In vivo dosimetry was done for two clinical cases using brass mesh.

Results: The phantom measurements revealed that the attenuation of the brass mesh bolus was 0.8% at 5 cm depth and 0.5% at 2 cm depth for 6MV. The brass mesh can thus be modeled as 3-mm tissue-equivalent-bolus in TPS. On ArcCHECK, the measurements showed that the brass mesh and the thermoplastic sheets produced similar surface doses, when no air gap present. With 1-cm air gap, surface dose decreased rapidly from medial to lateral. For the thermoplastic sheet, at 30°, the dose dropped by 3% and 10% compared to without air gap, for 6MV and 6FFF respectively; at the 45°, by 9% and 19% respectively. For the brass mesh, at 30°, there was almost no change in dose; at 45°, the dose dropped by only 5%. Brass mesh was used for two clinical cases. For a 3D CW, in vivo doses agree with Rx dose within 12%. For IMRT sarcoma, dose in groin area agreed with Rx dose within 4%.

Conclusion: We characterized dosimetry for brass mesh and its successful implementation for two challenging clinical cases. Additional results of VMAT CW and groin area applications for a Halcyon system will be presented.

Keywords

Not Applicable / None Entered.

Taxonomy

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

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