Ultrasound-CT fusion compared with MR-CT fusion for postimplant dosimetry in permanent prostate brachytherapy.
OBJECTIVE
Postplan evaluation is essential for quality assurance in prostate brachytherapy. MRI has demonstrated greater interobserver consistency in prostate contouring compared with CT. Although a valuable tool in postimplant assessment, MRI is costly and not always available. Our purpose is to compare dosimetry obtained using fusion of postimplant CT with preimplant transrectal ultrasound (TRUS) vs. CT-MR fusion.


METHODS
Twenty patients receiving permanent (125)I seed prostate brachytherapy underwent preimplant TRUS with urethrography, 1-month CT with a Foley catheter, and 1-month MRI. No patient received androgen deprivation therapy or external beam radiotherapy. The prescription dose of (125)I implant monotherapy was 144Gy. The preimplant TRUS and postimplant CT images were fused based on urethral position, and the CT-TRUS images were subsequently fused to the MRI using a seed-to-seed match. Dosimetric parameters for the ultrasound- and MR-derived prostate were compared.


RESULTS
The mean absolute difference between dosimetry from MRI or CT-TRUS fusion for D(90) was 3.2% and in V(100) was 1.2%. Only 1 patient had a difference in MR- and ultrasound-derived D(90) of more than 10% (11.4%) and only 1 had a difference in V(100) of more than 5%.


CONCLUSIONS
Fusion of preimplant TRUS with 1-month postimplant CT appears to lead to acceptable agreement with MR-based dosimetric parameters in postplan evaluation. TRUS-based volumes may be a reasonable alternative to MRI in settings where MRI is not available.
Department of Radiation Oncology, Nova Scotia Cancer Center, Halifax, Nova Scotia, Canada.
David
D
Bowes
Juanita M
JM
Crook
Cynthia
C
Araujo
Deidre
D
Batchelar
D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome; D014463:Ultrasonography / Q000379:methods*