Postimplant rectal dosimetry is not dependent on 103Pd or 125I seed activity•
Received 24 September 2009; received in revised form 3 December 2009; accepted 8 December 2009. published online 12 February 2010. Corrected Proof
Abstract
Purpose
In this study, the effect of prostate brachytherapy seed activity on postimplant rectal dosimetry was evaluated in Pro-Qura (Prostate Brachytherapy Quality Assurance; Seattle, WA) proctored, community-based programs.
Methods and Materials
Twenty-three hundred patients (1563 iodine-125 [125I] and 737 palladium-103 [103Pd]) from 78 brachytherapists with postimplant rectal dosimetry were identified. Seed activity was stratified into three tertiles for each isotope (≤0.300, 0.301–0.326, and >0.326mCi/seed for 125I and ≤1.330, 1.331–1.547, and >1.547mCi/seed for 103Pd). Postimplant dosimetry was performed in a standardized fashion. The rectum was contoured by outlining the outer rectal wall. The volume of the rectum receiving 100% of the prescription dose (R100) was calculated in cubic centimeters. The prostate V100 and D90 volumes were also calculated.
Results
The mean prostate volume was 35.8 and 32.3cm3 for 125I and 103Pd. The median time to postimplant CT was 30 days. For 125I, the V100 increased from 91.0% to 93.7% (p=0.012) and the D90 increased from 105.9% to 108.7% (p<0.001) for the lowest to the highest 125I seed activities. In contrast, no significant changes in V100 (p=0.751) or D90 (p=0.200) were discerned when stratified by seed activity. For both isotopes, there was no correlation between seed activity and R100, and R100 was highest for the intermediate seed activities. Overall, the R100 was lower for 103Pd vs. 125I (0.63 vs. 0.82cm3, p<0.001).
Conclusions
Within the confines of seed activities used in this study, higher activity seeds did not result in a deleterious effect on rectal dose. Higher activity seeds were associated with improved prostate dosimetry for 125I, whereas 103Pd dosimetry was not dependent on seed activity.
Corresponding author. Schiffler Cancer Center, 1 Medical Park, Wheeling, WV 26003. Tel.: +1-304-243-3490; fax: +1-304-243-5047.
• Conflicts of interest: John Sylvester and Peter Grimm are owners of Pro-Qura. Jonathan Khanjian is employed by Pro-Qura. No other conflicts of interest exist.
ABSTRACT
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