A guidance system is a virtual or physical device, or a group of devices implementing a controlling the movement of a ship, aircraft, missile, rocket, satellite, or any other moving object. (Wikipedia)
When you read the above quote, what comes to mind? For some, “guidance system” suggests their GPS navigation system to get them where they’re driving. For others, it suggests military use in warfare. On December 23, 1971 President Nixon signed into law what became known as the War Against Cancer. This metaphor is embedded in our national psyche. It’s common to hear people talk about their “battle with cancer” or their “fight to survive.” Cancer is indeed viewed as an enemy to be defeated.
If we keep that image, detecting and diagnosing prostate cancer (PCa) involves three key military steps:
- Intelligence (identify the precise location and size of enemy forces)
- Capture (penetrate the enemy to strategically take high-ranking prisoners for questioning)
- Interrogation (gain precise information about the nature and strategy of enemy troops)
Timing and accuracy are essential for victory. The precision and efficiency of these three steps is crucial.
In the world of prostate cancer, the guidance system used to provide intelligence about the location and size of suspected PCa, and to navigate the most precise and efficient capture for questioning will determine the appropriate battle plan, or treatment strategy, against the disease.
Comparing guidance systems
The three current guidance systems for knowledge about the enemy are multiparametric MRI (mpMRI), transrectal ultrasound (TRUS) and MRI/TRUS fusion.
The first, mpMRI, provides the most comprehensive image-based analysis of the prostate gland and nearby structures. It accomplishes both intelligence and capture. Each imaging sequence, or parameter, distinguishes specific characteristics of prostate tissue, so it excels at identifying the location and size of significant PCa—that is, potentially aggressive cells that require treatment to remove or destroy them. Once identified, this same technology is harnessed for real-time, in-bore MRI targeted biopsy using a minimal number of needles to capture “high-ranking” PCa cells, those at the core of the suspected tumor most likely to be the oldest and most aggressive. When sent to the pathology lab, these cells are interrogated at the microscopic and even genomic level to evaluate how dangerous they are. Treatment must be matched to these cells to avoid under-treatment and risk of recurrence.
The second guidance system, TRUS, is inadequate to visually identify suspected tumors because ultrasound does not differentiate cancer from normal tissue (researchers are working on “multiparametric ultrasound” because they recognize this deficiency, compared with MRI). Since today’s TRUS can’t define the size and location of the enemy, capturing PCa cells can’t be strategically targeted. Therefore, a TRUS biopsy uses a large number of needles to cast a wide net. Generally, 12 or more needle punctures are done, increasing the chance of pain, infection, bleeding and other side effects. What’s worse, however, is that such a scattershot approach fails to give a true portrait of the enemy. It tends to miss significant PCa while over-detecting insignificant PCa.
To compensate for the shortcoming of TRUS biopsy, imaging engineers have developed fusion, the third guidance system. This hybrid involves integrating previously captured mpMRI scans with real-time TRUS. In keeping with the principle of “what you see is what you get,” fusion is superior to TRUS alone because it takes advantage of what was seen on mpMRI. The problem with fusion lies in imperfect co-registration of visual elements (pixels) from the MRI digital images, which are not real-time, and live TRUS while the patient is positioned differently than he was during the MRI scan. And yet, fusion guidance is misleadingly called “MRI-guided biopsy”, which in our opinion lacks transparency. If no one explains to a patient that real-time, in-bore MRI targeting is more precise than fusion, patients believe they’re getting the same MRI advantages with fusion. They are not.
To drive home this point, a research/clinical team out of the University of Utah recognize the increasing use of fusion-guided biopsies, and posed the question whether the 12-core TRUS biopsy should be abandoned. They gathered data from 142 PCa patients who had both fusion and TRUS biopsies. They found that
- Both types had 79% agreement on finding any PCa, and 83% agreement on significant PCa.
- 15 patients (11%) were found to have a clinically significant cancer that would have been missed if fusion biopsy was omitted, and nine (6%) had a clinically significant cancer that would have been missed without 12-core biopsy.[i]
They concluded that for maximum accuracy, it is necessary to double up the two methods since neither alone is adequate. This is basically admitting that fusion is NOT MRI-guided in real-time. According to their protocol, both biopsy types should both be done in the same session! They will follow their own recommendation while they accumulate future data in hopes of eventually settling on a single method.
I have to ask, is this really necessary when research has already found that the single method is already here? Real-time, in-bore MRI targeted biopsy achieves the best of both worlds. At our Center, we continue to educate patients on the pitfalls of fusion, one of which is now adding a 12-core TRUS biopsy.
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] MedPage Today. “Matthew Parsons, MD, on Fusion vs 12-Core Biopsies.” May 5, 2021 https://www.medpagetoday.com/asco/non-prostate-genitourinary-cancer/92423 and McLean, Logan. “Concordance of MRI-guided and systemic prostate biopsy for the detection of prostate cancer (PCa).” ASCO. https://www.medpagetoday.com/reading-room/asco/non-prostate-genitourinary-cancer/92425