WE‐G‐BRE‐09: Targeted Radiotherapy Enhancement During Accelerated Partial Breast Irradiation (ABPI) Using Controlled Release of Gold Nanoparticles (GNPs)

Purpose: Several studies have demonstrated low rates of local recurrence with brachytherapy-based accelerated partial breast irradiation (APBI). However, long-term outcomes on toxicity (e.g. telangiectasia), and cosmesis remain a major concern. The purpose of this study is to investigate the dosimetric feasibility of using targeted non-toxic radiosensitizing gold nanoparticles (GNPs) for localized dose enhancement to the planning target volume (PTV) during APBI while reducing dose to normal tissue. Methods: Two approaches for administering the GNPs were considered. In one approach, GNPs are assumed to be incorporated in a micrometer-thick polymer film on the surface of routinely used mammosite balloon applicators, for sustained controlled in-situ release, and subsequent treatment using 50-kVp Xoft devices. In case two, GNPs are administered directly into the lumpectomy cavity e.g. via injection or using fiducials coated with the GNP-loaded polymer film. Recent studies have validated the use of fiducials for reducing the PTV margin during APBI with 6 MV beams. An experimentally determined diffusion coefficient was used to determine space-time customizable distribution of GNPs for feasible in-vivo concentrations of 43 mg/g. An analytic calculational approach from previously published work was employed to estimate the dose enhancement due to GNPs (2 and 10 nm) as a function of distance up to 1 cm from lumpectomy cavity. Results: Dose enhancement due to GNP was found to be about 130% for 50-kVp x-rays, and 110% for 6-MV external beam radiotherapy, 1 cm away from the lumpectomy cavity wall. Higher customizable dose enhancement could be achieved at other distances as a function of nanoparticle size. Conclusion: Our preliminary results suggest that significant dose enhancement can be achieved to residual tumor cells targeted with GNPs during APBI with electronic brachytherapy or external beam therapy. The findings provide a useful basis for developing nanoparticle-aided APBI, with potential to significantly reduce normal tissue/skin toxicity.