SU-FF-T-342: Peripheral Brachytherapy, Dosimetry, and Image Guidance Using the AccuBoost System

Abstract

Purpose: The Advance Radiation Therapy AccuBoost® system applies peripheral breast brachytherapy using combinations of stereotactic, parallel‐opposed HDR 192 Ir beams under mammographicimage guidance. Dosimetric characterization and commissioning for clinical use are presented. Materials and Methods: The AccuBoost system delivers a conformal boost with the breast compressed to 3–7 cm thickness between two mammography paddles using 5, 6, or 7 cm diameter applicators. This compressed breast geometry was simulated using experimental techniques and Monte Carlo methods. Measurements were performed in a 30×30 cm2 polystyrene phantom using a calibrated parallel‐plate ionization chamber positioned at depths of 0–7 cm along the central axis, and with either radiochromic film (GafChromic EBT) or computed radiography phosphor plate (Kodak Hres) placed parallel and normal to the phantom:applicator plane. The MCNP5 radiation transport code was used to simulate the HDR 192 Ir source, AccuBoost applicator, and compressed breast, assuming cylindrical symmetry. Dose was calculated with 1 mm resolution versus depth and radius for all breast thickness and applicator diameter combinations. Dosimetric results were reduced to a spreadsheet‐based lookup table for clinical implementation. Additional experiments were performed using a mammography system (GE Senographe 800T) and a CIRS breast phantom (model 051) containing radio‐opaque markers for image evaluation and marker localization. Results:Ionization chamber measurements and MC‐derived dose falloff agreed within 2%. Film measurements and MC‐derived relative dose profiles agreed within 6%. Skin/target dose ratio, for a dual axis exposure, varied from 0.5–1.1 over the wide range of applicator sizes and breast separations. Marker localization within 1 mm was achievable. Conclusions: The AccuBoost system can apply a conformal boost dose to the breast in a stereotactic configuration. The clinical environment may be readily simulated and treatment plans may be verified as evidenced by good agreement amongst the three dose measurement techniques. Disclosure: Research sponsored by Advanced Radiation Therapy.