Value of computed tomography in interstitial 125I brachytherapy of prostatic carcinoma

Computed tomography (CT) was performed in 20 patients with localized prostatic carcinoma before and after interstitial implantation of 125I seeds. Scans were analyzed to determine prostate volume, seed location, tumor response, and periprostatic tumor spread. CT volumes were an average of 25-30% greater than clinical estimates. In addition, CT demonstrated errors in implantation, including inhomogeneous distribution and extraprostatic seeds, in 17 patients (85%). Serial post-implantation scans showed no change in prostate volume in 12 patients (60%), a decrease in 7 (35%), and an increase in 1 (5%), concurring with clinical assessment of response to therapy. In 2 patients, clinically unsuspected tumor spread was identified on the CT scan.