By using MR in conjunction with MR spectroscopy, radiologists can improve the accuracy of prostate cancer diagnosis, researchers reported Thursday.Prostate cancer incidence and mortality are declining, but 160,000 diagnoses of the disease and 31,000 deaths were seen in the U.S. in 2001, according to Dr. Christopher Coogan of Rush-Presbyterian-St. Luke's Medical Center in Chicago. MRS shows great promise in locating tumors in patients considered high risk and in delineating the aggressiveness of tumor growth, he said.
Researchers from Memorial Sloan-Kettering Cancer Center in New York City performed a review of step section histopathologic tumor maps after radical prostatectomy was used to identify 18 patients with transition zone prostate cancer. Preoperative endorectal MRI was performed in all patients, and 3D spectroscopic imaging was performed in nine patients.
Seven of 18 tumors in the transition zone were identified as nonencapsulated soft-tissue masses of uniform intermediate T2-weighted signal intensity, and five of seven had ill-defined margins. Six of seven tumors 1.5 cm in diameter or greater were visible, compared with one of 11 less than 1.5 cm in diameter. MRS imaging was performed in four of these seven cases and showed a significant elevation of the choline peakin three patients.
The smaller transition zone tumors remained difficult to detect and tumor size was an important factor in visualization, according to Dr. Steven Eberhardt of Sloan-Kettering. Large transition zone tumors were frequently visible on endorectal MRI and MRS as ill-defined nonencapsulated soft-tissue masses of uniform intermediate T2-weighted signal intensity and a significant elevation of the choline peak.
Corroborating the effect of using MRS along with MR, researchers led by Dr. Fergus Coakley of the University of California, San Francisco performed endorectal MR imaging and 3D-MRSI in 37 patients prior to radical prostatectomy.
The mean volume of 51 peripheral zone tumor nodules was 0.79 cm3. Readers detected 20 and 23 of the 31 peripheral zone tumor nodules greater than 0.5 cm3. Tumor volume measurements of these nodules by MR imaging, 3D-MRSI, and combined MR imaging and 3D-MRSI were all positively correlated with histopathologic volume. But the only measurements to reach statistical significance were done by 3D-MRSI or combined MR imaging and 3D-MRSI.
All three methods of tumor volume estimation were more accurate at higher tumor volumes, according to Coakley. Adding 3D-MRSI to MRI increases the overall accuracy of prostate cancer tumor volume measurement, but measurement variability still limits tumor volume estimation, particularly for small tumors, he said.
