Comparison between high and low source activity seeds for I-125 permanent seed prostate brachytherapy.
OBJECTIVE
To compare low (mean 0.44, SD ± 0.0163 mCi) with high source activity (0.61 ± 0.0178 mCi) in I(125) permanent seed brachytherapy regarding seed loss, dosimetric outcome, and toxicity.


METHODS
The study included 199 patients with prostate cancer treated by permanent seed brachytherapy alone: the first 105 with seeds of lower activity (first cohort), the following 94 with higher seed activity (second cohort). The V100, V150, V200, and D90 were analyzed on the CT scan 30 days after implantation (CTD30). The V100, V150, and D2 of the rectum were also calculated on CTD30. Seed loss was determined 30 days after implantation. Urinary toxicity was measured with the International Prostate Symptom Score (IPSS) questionnaire.


RESULTS
Lower seed activity was associated with lower V150 and V200 (p = 0.01 and p ≤ 0.001, respectively) on CTD30. More patients had a V100 <90% and D90 <140 Gy in the lower activity cohort (p = 0.098 for D90 and p = 0.029 for V100) on CTD30. There was no difference between cohorts in dose to the rectum (p = 0.325-0.516) or difference in patients' IPSS score from baseline (p = 0.0.117-0.618), although there was a trend toward more urinary toxicity at 4 and 8 months for high activity seeds. Seed loss as a percentage of implanted seeds was not different (p = 0.324).


CONCLUSIONS
Higher seed activity (I(125) ≥ 0.6 mCi) results in at least equal V100 and D90 on CTD30. However, dose inhomogeneity and a trend toward more urinary toxicity at 4 and 8 months after treatment may lead to a higher long-term urinary complications.
Masucci
Giuseppina Laura
GL
Department of Radiation Oncology, Centre Hospitalier de l'Université de Montréal, Montreal, Canada.
Donath
David
D
Tétreault-Laflamme
Audrey
A
Carrier
Jean-François
JF
Hervieux
Yannick
Y
Larouche
Renée Xavière
RX
Bahary
Jean-Paul
JP
Taussky
Daniel
D
D000368:Aged; D001918:Brachytherapy / Q000009:adverse effects / Q000379:methods*; D015331:Cohort Studies; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects; D011795:Surveys and Questionnaires; D014057:Tomography, X-Ray Computed; D014555:Urination Disorders / Q000209:etiology
D007457:Iodine Radioisotopes