(Monday, 7/15/2019) 9:30 AM - 10:00 AM
Room: Exhibit Hall | Forum 3
Purpose: In standard standup technique for total skin irradiation, a pair of overlapping beams is required to cover the whole length of patient. This study aims to investigate the effect of scattering filter on the standard stand-up technique with a single beam.
Methods: The materials (Cu, Fe, Au, Zn, Ag) were chosen because of their stability and availability. The thickness ranges from 0.05 mm to 0.55 mm, depending on characteristics of materials. The extended source to skin distance (SSD) from 250 cm to 350 cm were studied. For each material, we vary the thickness and SSD, to evaluate following quantities: percent depth dose (PDD), profiles and output at dmax, and compared them with the standard dual beams at treatment SSD.
Results: No material shows acceptable profile flatness (±10% within the central 160 cm) at 250 cm SSD. At 300 cm SSD, Au (0.1 mm), Ag (0.25 mm), and Cu (0.45 mm) are acceptable. Zn (0.45 mm) requires 325 cm SSD to meet the requirement. For these 4 configurations, the dmax is 0.87-0.99 cm, similar to dual beam (0.97 cm); R₅₀ is 1.85-1.91 cm, compared with dual beam of 2.06 cm; the output ranges from 0.025-0.029, slightly lower than the dual beam (0.040). The composite fields for 4 configurations, the dmax is 0.1 cm, compared with dual beam (0.16 cm). The surface dose is 97%, similar to dual beam (96%). B-factor is 3.3-3.4, compared with dual beam (3.1). The maximum x-ray contamination is 3%, slightly higher than dual beam (2%).
Conclusion: The result of MC simulations suggests the stand-up TSI technique can be implemented using a single beam if the customized filter is used. Actual measurements will be performed to validate simulation results. MC simulation can be used to investigate the effect of filters and provide valuable guidance in future optimizations.
Keywords
Monte Carlo, Total Skin Irradiation, Electron Therapy
Taxonomy
TH- External beam- electrons: Monte Carlo dosimetry
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