A comparison of prostate iodine-125 seed dose planning using computed tomography and ultrasound imaging

Practitioners have used computed tomography (CT) or transrectal ultrasound (TRUS) imaging for planning the spatial distribution of radioactive seeds for patients with prostate cancer who are treated with transperineal implantation of iodine-125 seeds. It is known that the prostate volumes determined from CT and TRUS differ. These differences may affect the number of seeds implanted and total activity of the implant. We have planned 20 consecutive patients using both CT and TRUS imaging. The results of our study show that pre-implant prostate volumes are about 28% greater when determined from CT imaging compared with TRUS imaging. We also found that, for the patients selected in this study, 24% more seeds (and 25% more total activity) were required to encompass the CT target volume with the same dose contour as the TRUS target volume. Thus, the choice of imaging modality affects prostate brachytherapy planning and should be carefully considered when clinical protocols are designed.