Abstract
The purpose of this study was to examine the relationship between extraprostatic seed placement and seed loss in a cohort of patients who had underwent both computed tomographic (CT) and magnetic resonance (MR) scans at day 0 and day 30 following brachytherapy. Twenty-two patients with 1997 AJC clinical stage T1-T2 prostatic carcinoma were implanted with nonstranded I 125. Patients were selected solely by having a prostate volume between 15 and 60 cc and a willingness to return for 30-day follow-up CT and MR scans. The total number of I-125 sources implanted on day 0 ranged from 50 to 104 (median: 70). Preplan treatment planning methods have been previously described in detail: a modified peripheral loading pattern and treatment margins of 5-10 mm were used. Noncontrast postimplantation CT and MR scans were obtained 1-4 hours after implantation on day 0. The total seed count on days 0 and 30 was verified by plain radiograph. Pelvic MR (T1) images were registered with the CT images in the Varian planning system, using bony landmarks. The number of extracapsular seeds in each quadrant of the circumference was then totaled for each patient. A second set of plain radiographs (for seed counting), as well as CT and MR scans, were obtained 30 days after implantation (day 30) and were similarly analyzed. The number of extraprostatic seeds at day 0 ranged from 13 to 35, making up 17%-48% (median: 34%) of the total number implanted. Of the 22 patients, 10 lost one or more seeds between the implantation day and the 1-month follow-up. The mean number of seeds lost was 1.1 (+/- 1.7). There was no apparent relationship between the percent of extraprostatic seeds and the number of seeds lost. There was no apparent relationship between seed loss and number of seeds less than 3 mm or greater than 3 mm from the prostatic capsule. We have shown here that with CT and MR seed localization, extraprostatic seed placement does not appear to substantially increase the likelihood of seed loss after the procedure.
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