Department of Radiation Oncology, Princess Margaret Hospital, University Health Network, Toronto, Ontario, Canada.

To compare the critical organ dosimetry and toxicity of loose seeds (LS) with stranded seeds (SS) in (125)I permanent implant for low-risk prostate cancer.

Two cohorts of 20 patients each were treated in Institutional Review Board-approved protocols designed to assess prostate edema and seed stability using MR-CT fusion on Days 0, 7, and 30 after permanent implant. (125)I LS were used for one cohort and (125)I SS for the other. Rectal wall dosimetry was compared for the two cohorts using RV100 and RD1cc and urethral dosimetry using UD5, UD30, and UV150. Statistical comparisons were performed using unpaired Student's t test.

At each time point (Days 0, 7, and 30), both the mean RD1cc (SS: 123.1, 139.7, and 156.1Gy vs. LS: 90.2, 104, and 129.4Gy, respectively) and the mean RV100 (SS: 0.63, 1.0, and 1.4cc vs. LS: 0.2, 0.4, and 0.73cc, respectively) were significantly higher for strands (all p-values<0.01). Only 1 patient developed radiotherapy oncology group (RTOG) Grade 1 acute rectal toxicity in the loose seed cohort, whereas 3 patients had Grade 1 and 1 patient had Grade 2 toxicity with strands. The mean percentage increase of UD5 (7.7% LS vs. 24.6% SS; p=0.004) and UD30 (5% LS vs. 15.9% SS; p=0.02) from preplan to Day 30 was higher for strands. The increase in UV150 from baseline to Day 30 was significantly higher for strands (0.2 vs. 0.06cc; p=0.01). Urinary toxicity was similar in both cohorts.

SS resulted in higher dose to urethra and rectal wall compared with LS on postimplant dosimetry. A trend toward higher acute rectal toxicity rate was observed for SS.

Written by
Saibishkumar EP, Borg J, Yeung I, Cummins-Holder C, Landon A, Crook J.

Reference
Brachytherapy. 2008 Mar 22. Epub ahead of print.
doi:10.1016/j.brachy.2007.12.005

PubMed Abstract
PMID:18362087

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