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.