(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: To evaluate the accuracy of a Monte Carlo (MC) based treatment planning system (TPS) designed for treatment of superficial lesions with 50 kVp X-rays.
Methods: The RADIANCE TPS (GMV, Spain) uses a hybrid ray-tracing MC dose algorithm that accounts for photoelectric and Compton interactions. For a 50 kV INTRABEAM (Zeiss, Germany) source, 3D dose distributions were calculated for flat (F=1-6 cm) and surface (F=1-4 cm) applicators in water medium. Depth-dose rates for both flat and surface applicators were measured in water with a calibrated parallel plate ion chamber (IC). 2D dose distributions were obtained with radiochromic films in solid water for each applicator at various depths (d = 0, 5 & 10mm), and along the beam central axis (CAX). RADIANCE calculations were compared to IC and film measurements within MATLAB in order to investigate clinically relevant parameters: depth dose variations, surface dose, depth of maximum dose homogeneity dHMAX over central 80% of beam for flat applicators, and penumbra (80%-20% width).
Results: CAX percent depth doses agreed within 2% between MC calculations, IC measurements and film measurements. For 1Gy dose prescribed at 5 mm, the calculated surface dose varies with applicator type and size: up to 1.2 Gy for surface and 14 Gy for flat over 80% applicators diameter. Maximum dose homogeneity between RADIANCE and film measurements agree within 2%; dHMAX values agree within 1mm, ranging 5mm to 8mm depending on flat applicators size. The flat applicators penumbra is < 1 mm for depths shallower than dHMAX then increases up to 2cm for deeper depths. Surface applicators have larger penumbra widths which increase sharply up to 2~3 cm beyond 1cm depth.
Conclusion: RADIANCE TPS can accurately model dose distributions generated from INTRABEAM applicators. Dosimetric parameters relevant to clinical use were investigated to facilitate the design of superficial treatments.
Keywords
Monte Carlo, Low Energy X-rays, IORT
Taxonomy
TH- External Beam- Photons: Kilovoltage therapy
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