Loose seeds vs. stranded seeds: a comparison of critical organ dosimetry and acute toxicity in (125)I permanent implant for low-risk prostate cancer.
OBJECTIVE
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.


METHODS
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.


RESULTS
At each time point (Days 0, 7, and 30), both the mean RD1 cc (SS: 123.1, 139.7, and 156.1 Gy vs. LS: 90.2, 104, and 129.4 Gy, respectively) and the mean RV100 (SS: 0.63, 1.0, and 1.4 cc vs. LS: 0.2, 0.4, and 0.73 cc, 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. 0.06 cc; p=0.01). Urinary toxicity was similar in both cohorts.


CONCLUSIONS
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.
Saibishkumar
Elantholi P
EP
Department of Radiation Oncology, Princess Margaret Hospital, University Health Network, Toronto, ON, Canada.
Borg
Jette
J
Yeung
Ivan
I
Cummins-Holder
Cheryl
C
Landon
Angela
A
Crook
Juanita M
JM
D000328:Adult; D000368:Aged; D001918:Brachytherapy / Q000379:methods*; D004487:Edema / Q000175:diagnosis; D005548:Foreign-Body Migration / Q000175:diagnosis; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D012007:Rectum / Q000528:radiation effects; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D014521:Urethra / Q000528:radiation effects
D007457:Iodine Radioisotopes