SEATTLE-Improvements in standard imaging techniques may lead to enhanced prostate cancer detection and local staging accuracy in the near future, Gary Sudakoff, MD, said at the Pacific Northwest Cancer Foundation Meeting on Transperi-neal Brachytherapy for Early Stage Prostate Cancer. Such methods may include combining color Doppler imaging with endorectal ultrasound (see image ) and using new types of coils with magnetic resonance imaging (MRI), said Dr. Sudakoff, of the University of Chicago.
Traditionally, the digital rectal examination (DRE) has been the cornerstone of the preoperative diagnosis, he said. However, this technique has significant limitations. For example, many benign entities, such as benign prostatic hypertrophy (BPH), calculi, fibrosis, atrophy, infarc-tion, or cysts, are also palpable on DRE and may mimic cancer. On the other hand, malignant tumors, some significantly advanced, may not be palpable.
Dr. Sudakoff stressed that DRE should always be performed during the routine physical examination and that it still plays a major role in the diagnosis of early prostate pathology. But the combination of DRE and PSA levels provides a more accurate initial screening. If either is abnormal, then further evaluation with endorectal ultrasound (ERUS) and needle biopsy is warranted.
Although ERUS can detect masses that are not palpable on DRE, Dr. Sudakoff noted that it, too, has limitations. ERUS can detect abnormalities in the prostate but cannot accurately discriminate benign from malignant lesions.
Furthermore, he said, ERUS is limited in local staging of prostate cancers with accuracies approaching only about 60%. Another drawback: ERUS is a highly subjective and operator-dependent technique, and it may be less accurate in the hands of a less experienced examiner.
Thus, ERUS can be an excellent modality for use in detecting potential cancers and directing biopsy of these lesions, but because of its expense and limited accuracy, it should not be used alone for prostate cancer screening, he said.
Color Doppler Imaging
The lack of specificity of "gray scale" ERUS has recently been addressed with the development of color Doppler imaging. This technique allows the detection of both normal and abnormal vascular flow within tissue seen real-time during an ultrasound examination.
Cancers generally have abnormal vascular flow patterns and appear hyper-vascular compared to surrounding, normal tissue during color Doppler imaging. While most prostate cancers are typically hypoechoic, some may appear isoechoic and are not identifiable with gray scale ultrasound. These patients may be correctly identified with color Doppler during ERUS (see images ). Color Doppler imaging may then be used to further direct biopsy in these patients.
In addition, color Doppler can be used to improve discrimination between postsurgical scarring and recurrent or residual cancer in patients who are status post-prostatectomy, he said (see figure).
In an ongoing clinical study at the University of Chicago, ERUS alone correctly identified recurrent cancer with an accuracy of approximately 60%. Color Doppler alone had an accuracy of approximately 70%. Using a combined approach of ERUS with color Doppler yielded an accuracy of approximately 80%.
While preliminary, these data suggest that color Doppler imaging may play an important role in patients with a rising PSA who are status post-radical prosta-tectomy in detecting recurrent or residual carcinoma in the prostate fossa.
Recent improvements in computer software and receiver coils are greatly enhancing the accuracy of MRI in the diagnosis of prostate cancer, Dr. Sudakoff said. Because of its high soft-tissue contrast and multiplanar capability, MRI can be used to obtain a clear visual image of the prostate.
With the use of endorectal and phase array pelvic surface receiver coils, combined with an imaging technique known as fat suppression, MRI can often detect the site and extent of a prostate cancer. In particular, the ability to identify the prostatic capsule and capsular invasion into periprostatic fat or the seminal vesicle is now possible with accuracy rates reported between 70% and 85%.
In Dr. Sudakoff's opinion, MRI using these enhancement techniques is currently the best technique for noninvasive staging of prostate cancer.