The recent development of new prostate tracers has motivated us to build a low cost PET camera optimized to image the prostate. Coincidence imaging of positron emitters is achieved using a pair of curved detector banks. In this paper, we optimize the design of septa in the prostate camera for detecting prostate tumors. The performance of the system is measured using a prewhitening observer with a background-known-statistically task. The results show that the septa design has a large impact on lesion detection. At the background activity level of 0.1 /spl mu/Ci/cc, a novel septa design with 8-crystal spacing outperforms the traditional two-dimension (interplane septa) and three-dimension (septa-less) designs.