Dual Modality Implant for Simultaneous Magnetic Nanoparticle Heating and Brachytherapy Treatment of Tumor Resection Cavities in Brain

Hyperthermia (HT) has been shown to improve the clinical response of radiation therapy (RT) for cancer. The synergism is dramatically enhanced if HT and RT are combined simultaneously, but few technologies exist to apply treatments together. This study investigates feasibility of combining HT with RT using a thermobrachytherapy (TBT) balloon implant for treating a 5mm annular rim of at-risk tissue around a tumor resection cavity. For this approach, a balloon catheter was designed to deliver radiation from High Dose Rate brachytherapy simultaneously with HT delivered by filling a balloon with magnetic nanoparticles (MNP) and immersing the region in a radio frequency magnetic field. Temperature distributions in brain around the TBT balloon were simulated for typical brain blood perfusion using numerical modeling. A magnetic induction system was constructed and used to couple energy into MNP to heat tissue around balloon implants. Thermal dosimetry plans demonstrate our ability to heat a 5 mm annular rim of at-risk tissue around a brain tumor resection cavity between 40-48°C for 2-5 cm diameter balloon implants. The magnetic induction system produced rapid heating (>0.2°C/s) of MNP-filled balloons by depositing 0.6 W/ ml into the balloons with a magnetic field strength of 5.7 kA/m at 168 kHz, a level that has proven safe in previous clinical studies. These results demonstrate feasibility of using a thermobrachytherapy balloon implant for simultaneous heat and radiation treatment of tumor bed with both preclinical planning and experimental dosimetry.