Comparison of combined x-ray radiography and magnetic resonance (XMR) imaging-versus computed tomography-based dosimetry for the evaluation of permanent prostate brachytherapy implants.
OBJECTIVE
To present a method for the dosimetric analysis of permanent prostate brachytherapy implants using a combination of stereoscopic X-ray radiography and magnetic resonance (MR) imaging (XMR) in an XMR facility, and to compare the clinical results between XMR- and computed tomography (CT)-based dosimetry.


METHODS
Patients who had received nonstranded iodine-125 permanent prostate brachytherapy implants underwent XMR and CT imaging 4 weeks later. Four observers outlined the prostate gland on both sets of images. Dose-volume histograms (DVHs) were derived, and agreement was compared among the observers and between the modalities.


RESULTS
A total of 30 patients were evaluated. Inherent XMR registration based on prior calibration and optical tracking required a further automatic seed registration step that revealed a median root mean square registration error of 4.2 mm (range, 1.6-11.4). The observers agreed significantly more closely on prostate base and apex positions as well as outlining contours on the MR images than on those from CT. Coefficients of variation were significantly higher for observed prostate volumes, D90, and V100 parameters on CT-based dosimetry as opposed to XMR. The XMR-based dosimetry showed little agreement with that from CT for all observers, with D90 95% limits of agreement ranges of 65, 118, 79, and 73 Gy for Observers 1, 2, 3, and 4, respectively.


CONCLUSIONS
The study results showed that XMR-based dosimetry offers an alternative to other imaging modalities and registration methods with the advantages of MR-based prostate delineation and confident three-dimensional reconstruction of the implant. The XMR-derived dose-volume histograms differ from the CT-derived values and demonstrate less interobserver variability.
Acher
Peter
P
Division of Imaging Sciences, King's College London School of Medicine, London, UK. pete_acher@hotmail.com
Rhode
Kawal
K
Morris
Stephen
S
Gaya
Andrew
A
Miquel
Marc
M
Popert
Rick
R
Tham
Ivan
I
Nichol
Janette
J
McLeish
Kate
K
Deehan
Charles
C
Dasgupta
Prokar
P
Beaney
Ronald
R
Keevil
Stephen F
SF
D001918:Brachytherapy / Q000295:instrumentation*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D015588:Observer Variation; D011467:Prostate / Q000000981:diagnostic imaging / Q000473:pathology; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000532:radiotherapy*; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome
D007457:Iodine Radioisotopes