(A–C) The three anterior whole-body images are low count and are further degraded over time. Liver and blood pool activity is seen throughout the entire exam (arrows).

Differential Diagnosis

•  Bexxar therapy: Given the low-count and low-resolution images (I131 label) and given the prolonged imaging delay, this is consistent with Bexxar therapy. There is no evidence of altered biodistribution.

•  Zevalin therapy: Zevalin therapy has superior image quality, given the larger In111 dose (and better photon energies) used for pretreatment imaging (but with a similar biodistribution; see image at the bottom).

•  ProstaScint scan: Like Bexxar and Zevalin, ProstaScint is a radiolabeled antibody and hence has a similar normal biodistribution (largely blood pool and liver). However, it is not a therapeutic agent.

Essential Facts