ASTRO 07 Abstract

Purpose: The AccuBoost system (Advanced Radiation Therapy, Billerica, MA) applies breast brachytherapy without invasive catheters, and with mammographic image guidance using stereotactic localization of markers implanted during lumpectomy. This high-resolution imaging permits accurate localization of the region to be treated and assists with radiotherapy beam positioning. A combination of parallel-opposed HDR 192Ir beams are directed into the breast towards maximizing target dose uniformity and minimizing dose to skin and other healthy tissues. Pre-clinical studies examining dosimetric characterization and system commissioning for clinical use are presented.
Materials and Methods: The AccuBoost system is FDA-approved, and includes a fully-functional mammography system (model Senographe 800T by GE Healthcare, Piscataway, NJ), a computed radiography (CR) image analysis system (model CR 825 by Kodak, New Haven, CT) using a phosphor plate, three applicators with inner diameter ranging from 5-7 cm, and custom mammography paddles for precision applicator positioning on a compressed breast. The applicators have a single 6F catheter lead which is compatible with Nucletron and Varian HDR 192Ir remote afterloading systems. Patients treatments entail slight compression (3-7cm) of the breast, paddle positioning, mammographic imaging and CR plate exposure, image analysis and possible paddle repositioning, treatment delivery calculations with the appropriately sized applicator, and parallel-opposed irradiation. Towards benchmarking this novel treatment modality, localization accuracy based on image-guidance of the paddle/applicator assembly was assessed with a breast phantom (model 051 by CIRS, Norfolk, VA) containing radio-opaque markers under a variety of clinically-relevant conditions. Measurements (ionization chambers and GafChromic EBT film) were performed and compared to Monte Carlo (MCNP5) simulations of dose distributions as a function of depth, position, and for various breast compression thicknesses.
Results: Under all conditions, agreement of MC simulations with ion chamber results were within 2% for dose falloff and within 6% for dose profiles measured using film. For 4 orthogonal beams, calculated skin:target dose ratio varied between 0.5-1.1; more favorable results were observed for thinner compressed breast thicknesses. Marker localization within 1 mm was readily achievable, and imaging with 192Ir was examined.
Conclusions: Under image-guidance, the AccuBoost system can apply a conformal and uniform breast boost dose. MC simulations readily characterized the clinical environment as shown through agreement with measured results.