Use of pelvic CT scanning to evaluate pubic arch interference of transperineal prostate brachytherapy

Purpose: To determine the necessity of preoperative evaluation of pubic arc h interference in patients with small prostate volumes. Methods and Materials: CT scans from 97 consecutive, unselected patients wi th stage T1 or T2 prostatic carcinoma who had transperineal I-125 or Pd-103 implants at the University of Washington in 1997 were analyzed for pubic a rch interference, Transrectal ultrasound (TRUS) was performed with 6.0-MHz transducer with the patient in the lithotomy position and the patient's thi ghs vertical, similar to that used during the implant procedure, CT scans w ere obtained with the patient in the supine position, with 0.5-cm images ta ken at every 0.5 cm, To check for potential arch interference, the largest prostate cross-section was overlaid on the narrowest portion of the pubic a rch, The overlap of the pubic arch and the prostate margin is measured at r ight angles to the inner pubic surface. The prostate volume obtained from t he TRUS images was compared with the degree of pubic arch interference in o rder to determine whether TRUS volume predicted for interference. Results: There was considerable variability in pubic arch interference betw een patients. The mm of pubic arch overlap with the prostatic margin varied from -11 mm to 20 mm, Patients with larger prostate volumes generally had more pubic arch interference, but the degree of interference was only loose ly related to the prostate volume (r = 0.46). Conclusions: The degree of pubic arch interference is highly variable from one patient to the next and the TRUS volume cannot reliably predict patient s who do or do not need a pelvic CT to detect potential arch interference. (C) 1999 Elsevier Science Inc.