Suspicion of Prostate Cancer?
This Information Could Save Your Life.
Why Does This Matter?
A revolution is underway in the way prostate cancer is diagnosed. Traditionally, the standard method has been a 12-14 needle biopsy guided by transrectal ultrasound (TRUS). This approach is unreliable because it cannot differentiate cancerous tissue. It’s called a “systematic” biopsy because the prostate is divided into six sections on each side, with at least one sample taken from each section, totaling a minimum of 12 tissue samples.
The 3 Main Problems with TRUS Biopsy:
- It often detects insignificant prostate cancers that are unlikely to cause harm or require treatment.
- It frequently misses or fails to detect significant prostate cancers.
- It carries potential side effects, including infection, and the risk of underestimating more aggressive cancers, which could lead to recurrence after surgery or radiation.
The new, revolutionary diagnostic approach is to target only a few needles into the most suspicious areas of the prostate. This method significantly increases the chances of capturing the oldest, most aggressive cancer cells—those that are located where the tumor first developed—while also reducing the risk of infection and other side effects.
How Is the Core Identified Before Biopsy?
The key to this targeted approach is multiparametric MRI (mpMRI). Before the biopsy, an mpMRI scan is excellent at detecting significant prostate cancer. A skilled radiologist will assign a PI-RADS score ranging from 1 to 5, with category 5 indicating the highest likelihood of cancer. A score of 4 or 5 strongly suggests the presence of significant prostate cancer, which should be the primary area targeted for biopsy.
Once the biopsy samples are analyzed in a lab, they are given a Grade Group (GG) score from 1 to 5, with a GG of 2 or higher indicating that significant prostate cancer is present.
In-Bore MRI Targeting
What is the best method for targeting? A recent study by Prince et al. (2021)[i] compared real-time in-bore MRI-guided biopsy with fusion-guided biopsy.
“In-bore” refers to the process where the radiologist is able to see the tumor’s size, shape, and location in real-time while the patient is inside the MRI machine. This is made possible by the 3D, high-resolution capabilities of the MRI.
This method provides precise control and allows the radiologist to confirm the exact placement of a minimal number of needles (usually 2-4) directly into the core of the suspicious area. As a result, this biopsy technique has the smallest margin for error.
But Isn’t Fusion Also MRI-Guided?
Although fusion guidance does incorporate MRI images, it relies on an artificial process of point-by-point digitized co-registration (fusion) that aligns previously captured MRI scans with real-time ultrasound images. This process forces a fit between MRI scans taken when the patient is lying on their back and ultrasound views taken when the patient is lying on their side.
As the shift towards more targeted biopsies continues, urologists invest in fusion guidance because they genuinely want to improve patient care. They recognize that TRUS is inferior to MRI, so fusion is seen as a way to bring the advantages of MRI into the ultrasound-guided procedure.
However, the Prince study clearly points out that fusion “potentially risks misregistration error due to prostate deformation,” which the fusion process doesn’t account for. This means that while the doctor may believe the needle is correctly positioned, it may be slightly off when targeting the tumor. Even a small error can lead to significant consequences, such as missing the distinction between GG2 and GG3 cells—meaning an aggressive form of prostate cancer could go untreated, increasing the risk of recurrence.
Some urology practices may refer to their fusion-guided procedures as “MRI-guided targeted biopsies,” but this is misleading. Moreover, to address the targeting errors inherent in fusion, many of these biopsies also include a standard 12-needle systematic biopsy, in addition to the 2-4 targeted needles indicated by the software!
MRI-Guided Targeted Biopsy vs. Fusion-Guided Targeted Biopsy: Which is Better?
| MRI-GUIDED TARGETED BIOPSY | FUSION-GUIDED TARGETED BIOPSY |
| MRI imaging is conducted in real time while the patient lies in the MRI machine’s bore (tunnel). | Transrectal ultrasound is performed in real time in the urology exam room, but previously captured MRI scans are not live when integrated into the fusion software. |
| The patient is positioned on their back inside the magnet, and we do not use an endorectal coil (inserted into the rectum) at our Center. | The patient lies on their side on the examining table with the ultrasound probe inserted rectally. This different positioning introduces a margin of error during the point-by-point co-registration (fusion) of the prostate outline. |
| Real-time MRI imaging remains free from inaccuracies or distortion across multiple imaging sequences. | Fusion images may have some distortion, however small, due to – Co-registration error – Patient movement – Patient breathing, coughing or sneezing |
| MRI sequences distinguish tumor tissue from normal prostate tissue, allowing the radiologist to precisely identify the size, shape, and location of the targeted tumor in real time. | The urologist views the target based on images from a previous MRI fused with real-time ultrasound. However, real-time ultrasound cannot differentiate between tumor and normal prostate tissue within the gland, causing the software to create an artificial model of the prostate, which depicts the size, shape, and location of the targeted tumor. |
| Our prostate radiologists are highly experienced in interpreting MRI scans. | Urologists must be trained to read MRI images. |
| MRI-guided biopsy typically requires 2-4 needle samples. | Fusion targeting typically involves 2-4 needles directed into the computer-generated target, but fusion-guided biopsies often include an additional 12-needle systematic biopsy to compensate for potential inaccuracies in the fusion process. |
| This method eliminates the extra time spent on co-registration, which would otherwise involve gland segmentation and point-by-point alignment. | The procedure requires extra time for point-by-point co-registration and image matching. |
Results of the Study
MRI targeting performed in the bore (tunnel) of the magnet surpasses fusion, which is considered a less accurate substitute for the precision of real-time MRI. The Prince study highlights:
The relative precision of these two techniques is especially crucial if a target-only approach becomes the new diagnostic standard, as suggested by both the PROMIS and PRECISION trials. These trials concluded that an MRI-targeted biopsy strategy—without the use of standard systematic biopsies—would lead to more accurate prostate cancer diagnoses.
The authors compared the target-specific cancer detection rates of in-bore MRI versus fusion using a study sample of 286 men with mpMRI PI-RADS categories of 4 or 5.
The findings of the Prince study revealed that in-bore MRI-targeted biopsy of the prostate has a significantly higher target-specific cancer detection rate than fusion MRI-targeted biopsy.
Great results!