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.