PHSOR03 Presentation Time: 12:40 PM: Radiation Dosimetry of a Dual-Modality Balloon Implant for Simultaneous HDR Brachytherapy and Magnetic Nanoparticle Hyperthermia to Treat Brain Tumor Resection Cavities

Abstract

<h3>Purpose</h3> Glioblastoma multiforme (GBM) is an aggressive brain tumor that generally recurs locally and has a dismal median survival of less than 18 months<i>. In vivo</i> studies have shown that simultaneous hyperthermia and radiation can enhance the radiation response by a factor of up to 5. Our group developed a novel dual-modality thermobrachytherapy (TBT) balloon device to accomplish this goal. The balloon will combine magnetic fluid hyperthermia and HDR brachytherapy, which will be delivered right after brain tumor resection, so that the at-risk tissue adjacent to the tumor resection cavity will conform to the balloon shape and receive uniform radiation and thermal dose. This abstract focuses on the possible effects of hyperthermia on radiation dosimetry as well as the effects of balloon shape. <h3>Methods</h3> The current version of our TBT balloon device consists of a balloon filled with magnetic nanoparticle solution (nanofluid) and a flexible sheath with three ports to insert the HDR catheter and fiber-optic thermal probe and inject the nanofluid. We tested the balloon in air and activated the nanofluid using an external magnetic field induced by a 133 kHz induction coil. Two balloon designs were tested: a spherical one with 4 cm diameter, and a teardrop-shaped balloon with an axial diameter of 3 cm and measuring 3.7 cm along the shaft. We used Gafchromic film and RIT imaging software to analyze the in-air dose distribution of an HDR source dwell in both types of balloons, filled with distilled water and then nanofluid, as well as without and with simultaneous hyperthermia, where the coil power was escalated until reaching intra-balloon temperatures greater than 55°C. Experimental setup and radiation dose profiles can be found in Figure 1. <h3>Results</h3> The presence of the nanofluid, magnetic field and heat up to 66°C did not affect radiation dose distribution significantly in the spherical balloon (less than 10% difference). However, the teardrop-shaped balloon dose profiles showed a notable difference (about 20%) in dose magnitude with the presence of nanofluid and/or heat. Nonetheless dose distributions looked symmetrical in all cases. <h3>Conclusions</h3> The current device design is still in progress, but this study illustrated that a spherical balloon shape may be preferential for simultaneous hyperthermia and HDR brachytherapy. Furthermore, this radiation dosimetry study demonstrated compatibility and robustness of the prototype balloon components and desirable symmetrical dose distribution.