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Magnetic resonance imaging (MRI) provides superior visualization of the prostate and surrounding anatomy, making it the modality of choice for imaging the prostate gland. This pilot study was performed to determine the feasibility and dosimetric quality achieved when placing high-dose-rate prostate brachytherapy catheters under MRI guidance in a standard “closed-bore” 1.5T scanner.
Methods and Materials:
Patients with intermediate-risk and high-risk localized prostate cancer received MRI-guided high-dose-rate brachytherapy boosts before and after a course of external beam radiotherapy. Using a custom visualization and targeting program, the brachytherapy catheters were placed and adjusted under MRI guidance until satisfactory implant geometry was achieved. Inverse treatment planning was performed using high-resolution T2-weighted MRI.
Ten brachytherapy procedures were performed on 5 patients. The median percentage of volume receiving 100% of prescribed minimal peripheral dose (V100) achieved was 94% (mean, 92%; 95% confidence interval, 89–95%). The urethral V125 ranged from 0% to 18% (median, 5%), and the rectal V75 ranged from 0% to 3.1% (median, 0.3%). In all cases, lesions highly suspicious for malignancy could be visualized on the procedural MRI, and extracapsular disease was identified in 2 patients.
High-dose-rate prostate brachytherapy in a standard 1.5T MRI scanner is feasible and achieves favorable dosimetry within a reasonable period with high-quality image guidance. Although the procedure was well tolerated in the acute setting, additional follow-up is required to determine the long-term safety and efficacy of this approach.
PMCID: PMC2396328  PMID: 15275727
Prostate cancer; Brachytherapy; MRI; Image guidance
2.  Intra- and inter-radiation therapist reproducibility of daily isocenter verification using prostatic fiducial markers 
We sought to determine the intra- and inter-radiation therapist reproducibility of a previously established matching technique for daily verification and correction of isocenter position relative to intraprostatic fiducial markers (FM).
Materials and methods
With the patient in the treatment position, anterior-posterior and left lateral electronic images are acquired on an amorphous silicon flat panel electronic portal imaging device. After each portal image is acquired, the therapist manually translates and aligns the fiducial markers in the image to the marker contours on the digitally reconstructed radiograph. The distances between the planned and actual isocenter location is displayed. In order to determine the reproducibility of this technique, four therapists repeated and recorded this operation two separate times on 20 previously acquired portal image datasets from two patients. The data were analyzed to obtain the mean variability in the distances measured between and within observers.
The mean and median intra-observer variability ranged from 0.4 to 0.7 mm and 0.3 to 0.6 mm respectively with a standard deviation of 0.4 to 1.0 mm. Inter-observer results were similar with a mean variability of 0.9 mm, a median of 0.6 mm, and a standard deviation of 0.7 mm. When using a 5 mm threshold, only 0.5% of treatments will undergo a table shift due to intra or inter-observer error, increasing to an error rate of 2.4% if this threshold were reduced to 3 mm.
We have found high reproducibility with a previously established method for daily verification and correction of isocenter position relative to prostatic fiducial markers using electronic portal imaging.
PMCID: PMC1436003  PMID: 16722575

Results 1-2 (2)