Prostate Postbrachytherapy Seed Distribution: Comparison of High-Resolution, Contrast-Enhanced, T1- and T2-Weighted Endorectal Magnetic Resonance Imaging Versus Computed Tomography: Initial Experience
To compare contrast-enhanced, T1-weighted, three-dimensional magnetic resonance imaging (CEMR) and T2-weighted magnetic resonance imaging (T2MR) with computed tomography (CT) for prostate brachytherapy seed location for dosimetric calculations.
Postbrachytherapy prostate MRI was performed on a 1.5 Tesla unit with combined surface and endorectal coils in 13 patients. Both CEMR and T2MR used a section thickness of 3 mm. Spiral CT used a section thickness of 5 mm with a pitch factor of 1.5. All images were obtained in the transverse plane. Two readers using CT and MR imaging assessed brachytherapy seed distribution independently. The dependency of data read by both readers for a specific subject was assessed with a linear mixed effects model.
The mean percentage (+/- standard deviation) values of the readers for seed detection and location are presented. Of 1205 implanted seeds, CEMR, T2MR, and CT detected 91.5% +/- 4.8%, 78.5% +/- 8.5%, and 96.1% +/- 2.3%, respectively, with 11.8% +/- 4.5%, 8.5% +/- 3.5%, 1.9% +/- 1.0% extracapsular, respectively. Assignment to periprostatic structures was not possible with CT. Periprostatic seed assignments for CEMR and T2MR, respectively, were as follows: neurovascular bundle, 3.5% +/- 1.6% and 2.1% +/- 0.9%; seminal vesicles, 0.9% +/- 1.8% and 0.3% +/- 0.7%; periurethral, 7.1% +/- 3.3% and 5.8% +/- 2.9%; penile bulb, 0.6% +/- 0.8% and 0.3% +/- 0.6%; Denonvillier's Fascia/rectal wall, 0.5% +/- 0.6% and 0%; and urinary bladder, 0.1% +/- 0.3% and 0%. Data dependency analysis showed statistical significance for the type of imaging but not for reader identification.
Both enumeration and localization of implanted seeds are readily accomplished with CEMR. Calculations with MRI dosimetry do not require CT data. Dose determinations to specific extracapsular sites can be obtained with MRI but not with CT.
Available from: PubMed Central
- "For this purpose, a number of automated identification methods for locating radioactive iodine-125 seeds and ascertaining the number of seeds for prostate brachytherapy have been developed based on three-dimensional (3D) reconstructed images by use of fluoroscopy images or digitized radiographs [19–21], computed tomography (CT) [22–24], magnetic resonance imaging (MRI) [25, 26] and tomosynthesis [27, 28]. However, it is difficult to employ imaging modalities such as CT or MRI in the operating room. "
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ABSTRACT: Digital pelvic radiographs are used to identify the locations of implanted iodine-125 seeds and their numbers after insertion. However, it is difficult and laborious to visually identify and count all implanted seeds on the pelvic radiographs within a short time. Therefore, our purpose in this research was to develop an automated method for estimation of the number of implanted seeds based on two-view analysis of pelvic radiographs. First, the images of the seed candidates on the pelvic image were enhanced using a difference of Gaussian filter, and were identified by binarizing the enhanced image with a threshold value determined by multiple-gray level thresholding. Second, a simple rule-base method using ten image features was applied for false positive removal. Third, the candidates for the likely number of a multiply overlapping seed region, which may include one or more seeds, were estimated by a seed area histogram analysis and calculation of the probability of the likely number of overlapping seeds. As a result, the proposed method detected 99.9% of implanted seeds with 0.71 false positives per image on average in a test for training cases, and 99.2% with 0.32 false positives in a validation test. Moreover, the number of implanted seeds was estimated correctly at an overall recognition rate of 100% in the validation test using the proposed method. Therefore, the verification time for the number of implanted seeds could be reduced by the provision of several candidates for the likely number of seeds.
Available from: Robert W Laing
- "Post-implant dosimetry at our centre is routinely acquired on day 1, and with the use of CT imaging. We acknowledge that T2-weighted magnetic resonance imaging is superior over 5 mm CT slices particularly when defining the prostatic apex and extracapsular sites such as the penile bulb and neurovascular bundles . We have reported results derived from standard practice at our centre, which as yet does not involve the use of MRI; however, we anticipate the future use of this technology, which will hopefully enhance the accuracy of reported apical and bulb dosimetry. "
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ABSTRACT: Erectile dysfunction following prostate brachytherapy is reported to be related to dose received by the penile bulb. To minimise this, whilst preserving prostate dosimetry, we have developed a technique for I-125 seed brachytherapy using both stranded seeds and loose seeds delivered with a Mick applicator, and implanted via the sagittal plane on trans-rectal ultrasound.
Post-implant dosimetry and potency rates were compared in 120 potent patients. In Group 1, 60 patients were treated using a conventional technique of seeds implanted in a modified-uniform distribution. From January 2005, a novel technique was developed using stranded seeds peripherally and centrally distributed loose seeds implanted via a Mick applicator (Group 2). The latter technique allows greater flexibility when implanting the seeds at the apex. Each patient was prescribed a minimum peripheral dose of 145 Gy. No patients received external beam radiotherapy or hormone treatment. There was no significant difference in age or pre-implant potency score (mean IIEF-5 score 22.4 vs. 22.6, p=0.074) between the two groups.
The new technique delivers lower penile bulb doses (D(25) as %mPD - Group 1: 61.2+/-35.7, Group 2: 29.7+/-16.0, p<0.0001; D(50) as %mPD - Group 1: 45.8+/-26.9, Group 2: 21.4+/-11.7, p<0.0001) whilst improving prostate dosimetry (D(90) - Group 1: 147 Gy+/-21.1, Group 2: 155 Gy+/-16.7, p=0.03). At 2 years, the potency rate was also improved: Group 1: 61.7%; Group 2: 83.3% (p=0.008).
In this study, the novel brachytherapy technique using both peripheral stranded seeds and central loose seeds delivered via a Mick applicator results in a lower penile bulb dose whilst improving prostate dosimetry, and may achieve higher potency rates.
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ABSTRACT: Klinisches/methodisches Problem
Für Patienten mit Prostatakarzinom stellt die Radiatio eine potenziell kurative lokale Therapieoption dar. Im Rahmen der Nachsorge nach lokal kurativ intendierter Therapie wird aktuell der Verlauf des PSA-Werts (PSA prostataspezifisches Antigen) kontrolliert, der Einsatz bildgebender Verfahren wird lediglich bei symptomatischen Patienten und/oder zur Planung einer Salvagetherapie empfohlen.
Die MRT der Prostata stellt derzeit die Methode der Wahl zur lokalen Rezidivdiagnostik dar.
Insbesondere in Verbindung mit funktionellen Untersuchungstechniken zeigen Studien gute Ergebnisse in der Primärdiagnostik. Zum Einsatz der MRT der Prostata in der Rezidivsituation wurden bisher nur wenige Studien mit heterogenem Studiendesign publiziert. Auch die in der MRT nach Bestrahlung sichtbaren Veränderungen in den unterschiedlichen Modalitäten sind noch wenig evaluiert.
Empfehlung für die Praxis
Da die ersten Studienergebnisse auch bei Patienten nach Radiatio viel versprechend sind, sollte bei unklarem PSA-Anstieg und vorhandener Therapieoption eine MRT der Prostata zur Klärung der lokalen Situation in Betracht gezogen werden.
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