If your PSA is unusually high or your digital rectal exam finds an abnormality, how do you know if it’s prostate cancer? Magnetic resonance imaging (MRI) is now the universally preferred noninvasive method for identifying prostate cancer (PCa) prior to having a biopsy.
In the years leading up to this, researchers worked toward agreement over which imaging sequences or parameters to use during the scan, and how to score them using the PI-RADS scale. Why was it so important to reach agreement? Well, I’m reminded of the folk tale about the six blind men trying to describe an elephant. It’s a great lesson on how unproductive it is to cling to your own perceptions. The man who feels the tail thinks the animal is like a rope. Another who feels the trunk says the beast is like a snake. A third who touches the tip of a tusk says it’s like spear, and so on. They end up arguing, each insisting he is right. Finally, a wise person suggests that they can arrive at the correct answer by cooperatively sharing their views.
Assembling diverse assumptions and viewpoints to arrive at a cooperative conclusion is called a consensus process. In the early days of using MRI for PCa detection, radiologists relied on keeping abreast of published studies and attending conferences where they could listen to presentations and dialogue with each other. Exchanging theories, techniques and results in this way was in the best interests of patients everywhere, and. However, it was inefficient, so eventually consensus models were used in order to focus on creating standards for MRI applied to men newly suspected of having PCa.
Agreeing on MRI for suspected recurrence
What about those men whose initial PCa was correctly diagnosed, and who subsequently had radical prostatectomy or radiation? As many as 25% of them eventually have a rising PSA sometime after treatment, almost always a sign that their PCa has returned. This is called biochemical recurrence since it’s based on the PSA biomarker. The task is to determine the its level of aggression, location and extent of recurrence. MRI is the preferred initial scan to detect if the lesion is localized and qualifies for a potentially curative salvage treatment, and to rule out metastasis (spread) that would require a systemic therapy to manage the disease and lengthen survival time. The problem, however, is that recurrent lesions may appear differently on MRI than the original tumor. Treatment artifacts like scarring, etc. may confound the results and lead to misinterpretation.
Because of this, there has been international variability in how each imaging center has conducted and interpreted the MRI scans. Therefore, like the six men who had different limited experiences of elephant parts, it was essential to compare notes and come to agreed-upon standards.
Thus, a panel of international experts was formed to synthesize all available evidence and create a structured system for image acquisition, interpretation and reporting on cases of biochemical recurrence. Through face-to-face and online discussions, they created a method similar to PI-RADS, and named it Prostate Imaging for Recurrence Reporting (PI-RR). They successfully determined “…acceptable MRI parameters for detection of recurrence after radiation therapy and radical prostatectomy… Also, a simplified standardized terminology and content of the reports that use five assessment categories to summarise the suspicion of local recurrence…”[i] Their scoring categories are:
- PI-RR scores 1 and 2 – very low and low likelihood of recurrence
- PI-RR score of 3 – the presence of recurrence is uncertain
- PI-RR scores of 4 and 5 – high and very high likelihood of recurrence
They note that PI-RR is “intended to be used in routine clinical practice and to facilitate data collection and outcome monitoring for research.” PI-RR will thus not only be advantageous for patients and their doctors, but will also form the basis for apples-to-apples clinical studies.
It’s reassuring to know that top authorities have determined criteria that serve all patients equally, especially when there’s so much at stake with identifying recurrence as early as possible. In this way, we all gain the very best that MRI is capable of.
NOTE: This content is solely for purposes of information and does not substitute for diagnostic or medical advice. Talk to your doctor if you are experiencing pelvic pain, or have any other health concerns or questions of a personal medical nature.
[i] Panebianco V, Villeirs G, Weinreb JC, Turkbey BI et al. Prostate Magnetic Resonance Imaging for Local Recurrence Reporting (PI-RR): International Consensus -based Guidelines on Multiparametric Magnetic Resonance Imaging for Prostate Cancer Recurrence after Radiation Therapy and Radical Prostatectomy. Eur Urol Oncol. 2021 Dec;4(6):868-876.