WE‐A‐108‐09: Interstitial Rotating Shield Brachytherapy for Prostate Cancer

Purpose: To introduce a feasible interstitial rotating shield brachytherapy (I‐RSBT) system for treating prostate cancer. With I‐RSBT, the radiation sources are surrounded by catheters that contain shields to enable conformal avoidance of healthy tissues, potentially reducing complications relative to conventional high‐dose‐rate brachytherapy (HDR‐BT) techniques. Methods: The I‐RSBT system is based around ten control cartridges with 9.5 mm × 9.5 mm cross sections. Each control cartridge contains a rotational stepper motor, connected to a lead screw, which drives a platinum‐shielded nitinol catheter containing a 37 GBq Gd‐153 source. Gadolinium‐153 is generated by neutron irradiation of europium‐151 or Gd‐152 and is mass‐producible at reasonable cost. For I‐RSBT delivery, the cartridges are arranged in a box‐shaped magazine in a desired delivery pattern and aligned with a template containing implanted 16 gauge interstitial nitinol needles. Each source/catheter travels down a needle in a helical pattern during the dose delivery process. An I‐RSBT delivery using more than ten needles can be accomplished by dividing the treatment into multiple parts, each with a different cartridge arrangement in the magazine. Results: Treatment plans based on Monte Carlo dose calculations and optimized using the linear least squares technique demonstrated I‐RSBT reduced D1% (minimum dose to hottest 1%) for the urethra and rectum by 20% and 10% respectively, relative to conventional HDR‐BT. The prostate D97% was the same for I‐RSBT as for HDR‐BT. The I‐RSBT treatment time for a 20 Gy delivery would be 3 hours with fresh Gd‐153 sources. Since Gd‐153 has substantially lower gamma ray energies than iridium‐192, I‐RSBT treatments can occur in procedure rooms rather than conventional brachytherapy suites, reducing the disadvantage of the longer I‐RSBT delivery times. Conclusions: Treating prostate cancer with I‐RSBT is technically feasible in reasonable treatment times using platinum‐shielded Gd‐153 sources and the proposed delivery system. University of Iowa Research Foundation