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Brachytherapy. 2012 Nov-Dec;11(6):489-94. doi: 10.1016/j.brachy.2011.07.004. Epub 2011 Aug 24.

Timing of postseed imaging influences rectal dose-volume parameters for cesium-131 prostate seed implants.

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Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, NY 10467, USA.



To study the influence of timing of postseed implant imaging on rectal dose-volume parameters for cesium-131 ((131)Cs) seed prostate implants.


Fifteen patients were treated in our institution with combination (131)Cs brachytherapy followed by pelvic external beam radiation therapy for intermediate to high-risk prostate cancers. For all patients, CT scans were scheduled at 7 days (CT(7)) and again at 2 months for external beam radiation therapy simulation purpose (CT(60)) postseed implantation. Comprehensive postseed implant dosimetry was performed for both CT(7) and CT(60) scans. In each case, dose-volume histogram parameters, rectal separation (the distance between the center of posterior most seed and most anterior rectal wall), and posterior row activity (the total activity implanted within 2-4mm anterior to the posterior wall of the prostate) data were collected. The absolute rectal volumes receiving 100% and 110% prescription dose were also collected.


Rectal dose correlated strongly with rectal separation (p<0.001). The mean change in rectal separation between CT(7) and CT(60) scans was 1.1 (±1.7) mm, and the corresponding change in 0.1-cc rectal dose was 18 (±26.5) Gy. Posterior row activity did not correlate with rectal dose (p=0.51). The mean volume of rectum that receives between 100% and 110% of the prescription dose (RV(100) and RV(110)) increased twofold, between CT(7) and CT(60) evaluations (0.03 [±0.06] cc vs. 0.07 (±0.05) cc, respectively, p=0.06).


Our study has demonstrated that rectal doses after (131)Cs seed implants are influenced by the timing of postseed imaging. This may be a consequence of prostatic and periprostatic edema resolution.

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