Scatter Radiation from Palladium-103 Prostate Seed Implants on Bone Scan

A 65-year-old man with prostate cancer underwent a bone scan for evaluation of metastatic disease and left second and third metatarsal fractures using 15.89 mCi Tc-99m MDP. He was status post insertion of one hundred thirteen 0.97-mCi prostatic TheraSeed palladium-103 implants (110 mCi). Although 20 to 23 keV characteristic radiographs are the most significant in terms of treatment dose, higher-energy gamma emissions of low abundance (297 keV = 0.011%, 362 keV = 0.060%, 498 keV = 0.011%) are responsible for scatter seen in the pelvis on a Tc-99m MDP bone scan. Because the palladium-103 half-life is 16.97 days, this interference will persist for weeks after seed implantation.