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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.

Author information

1
Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, NY 10467, USA. ryaparpa@montefiore.org

Abstract

PURPOSE:

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

METHODS AND MATERIALS:

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.

RESULTS:

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).

CONCLUSIONS:

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.

PMID:
21868289
DOI:
10.1016/j.brachy.2011.07.004
[Indexed for MEDLINE]
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