MR imaging for prostate cancer staging: beauty or beast?

It has long been expected that magnetic resonance (MR) imaging would be helpful in pretherapy evaluation of earlystage prostate cancer, primarily to detect extraprostatic cancer extension beyond the reach of the knife or the prescription isodose. But despite the striking beauty of good quality MR images, it has yet to live up to expectations. Sensitivity to detect pathologically proven subclinical extraprostatic cancer extension (EPE) is 50% at best (1–3). And when MR demonstrates EPE, the chance that it really exists (positive predictive value) is only approximately 50%. When correlated with pathologic findings, MR has consistently fallen short of sufficient accuracy to warrant routine clinical use. Just when imaging specialists have tried and failed to show that MR is ready for routine clinical use, Clarke and colleagues come along and claim that their patient series supports its use (4). Hmmm . . . Drs. Clarke, Banks, and colleagues present clinical outcomes of 327 patients staged with MR and treated with brachytherapy supplemental beam radiation, guided by their MR findings They conclude that the excellent biochemical outcomes were due, in part, to the MR staging. I doubt it. While the results appear very, very good, I am completely unconvinced that MR staging had a significant role in the outcomes. The authors’ principal argument for the utility of MR is that most of their patients did well. Nonsense. The reason the patients did well was more likely that the authors did good implants, not because they ordered MR scans. In fact, more and more brachytherapists are reporting very high rates of biochemical control with brachytherapy alone, without routine MR staging (4–6). The 94% cure rate that Clarke points to as circumstantial evidence supporting routine MR imaging fails to convince me that he is achieving results any better than what other brachytherapy enthusiasts can routinely achieve without it. Dr. Clarke’s second argument for MR staging is that it can reliably identify extracapsular disease, directing the use of extra sources or supplemental beam radiation. In fact, studies now cast substantial doubt on such rationale for supplemental beam radiation, providing that a good quality implant is done to cover the maximal 3.0 mm extraprostatic cancer extension that typically exists at the prostatic capsule or base of the seminal vesicles (7–9). The authors’ third argument for the utility of preimplant MR staging is that patients without it did poorly. I don’t buy it—if this were true, how could other investigators routinely achieve such high biochemical cure rates without using MR? (5, 10) Surely there are explanations other than lack of MR staging for the inferior outcomes in the cohort of nonimaged patients. MR—is it beauty or beast? I think it’s both. The images are beautiful, striking in their delineation of tissue planes. But alas, I suspect that with current technology its beauty is only film deep. And it is a beast—expensive technology without a legitimate role in routine clinical staging. Working in the confines of the Veterans Affairs budget, I bristle at unfounded claims of another expensive technology being a valuable addition to what is currently an efficient, remarkably effective therapy for early-stage prostate cancer (11). To Drs. Clarke and Banks I say congratulations on your brachytherapy technique. Don’t misdirect the credit toward MR imaging.