MR and CT image fusion for postimplant analysis in permanent prostate seed implants.
OBJECTIVE
To compare the outcome of two different image-based postimplant dosimetry methods in permanent seed implantation.


METHODS
Between October 1999 and October 2002, 150 patients with low-risk prostate carcinoma were treated with (125)I and (103)Pd in our institution. A CT-MRI image fusion protocol was used in 21 consecutive patients treated with exclusive brachytherapy. The accuracy and reproducibility of the method was calculated, and then the CT-based dosimetry was compared with the CT-MRI-based dosimetry using the dose-volume histogram (DVH) related parameters recommended by the American Brachytherapy Society and the American Association of Physicists in Medicine.


RESULTS
Our method for CT-MRI image fusion was accurate and reproducible (median shift <1 mm). Differences in prostate volume were found, depending on the image modality used. Quality assurance DVH-related parameters strongly depended on the image modality (CT vs. CT-MRI): V(100) = 82% vs. 88%, p < 0.05. D(90) = 96% vs. 115%, p < 0.05. Those results depend on the institutional implant technique and reflect the importance of lowering inter- and intraobserver discrepancies when outlining prostate and organs at risk for postimplant dosimetry.


CONCLUSIONS
Computed tomography-MRI fused images allow accurate determination of prostate size, significantly improving the dosimetric evaluation based on DVH analysis. This provides a consistent method to judge a prostate seed implant's quality.
Polo
Alfredo
A
Division of Radiation Oncology, European Institute of Oncology, Milan, Italy. apolo@csub.scs.es
Cattani
Federica
F
Vavassori
Andrea
A
Origgi
Daniela
D
Villa
Gaetano
G
Marsiglia
Hugo
H
Bellomi
Massimo
M
Tosi
Giampiero
G
De Cobelli
Ottavio
O
Orecchia
Roberto
R
D000368:Aged; D000465:Algorithms; D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010165:Palladium / Q000627:therapeutic use; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011868:Radioisotopes / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods*
D007457:Iodine Radioisotopes; D011868:Radioisotopes; D010165:Palladium