Prostate Cancer Diagnosis
Read about the differences between standard and fusion biopsy procedures and discover why Fusion Bx is better for your business.
Standard Biopsy Limitations
Traditionally, men suspected of prostate cancer undergo systematic biopsies guided by ultrasound imaging. Because ultrasound offers poor cancer visualization, 12 random samples are taken without knowing if there is cancer and if so, where it is. As a result, the cancer is either missed entirely, or if detected, is difficult to determine the extent and severity. This leads to under treatment of men with serious disease and overtreatment of men with indolent disease.4
Detecting clinically significant cancer depends on two diagnostic qualities:
1. Accuracy- how close to the truth a diagnostic test is
2. Reliability- how reproducible a test is
Prostate cancer is multifocal and microscopic. Detecting it requires sampling at least a few cancerous cells in 10- 12 cores. It requires high specificity; you need to know where the cancer is and more importantly, where it is not.2 The prostate remains the only organ where a blind sampling technique is standard practice. This is due to the poor visibility of cancer in 2D TRUS images and limited anatomical context to guide needles to suspicious locations in the 2D TRUS plane.3
MRI-targeted biopsies offer a solution to inaccurate, or lack thereof, prostate cancer localization. Compared to TRUS, MRI can be considered the “Gold Standard” for detecting lesions.10 “The excellent resolution and high signal-to-noise ratio provided by MRI, combined with the functional measurements of water diffusion and contrast enhancement give an improved insight into the underlying histopathology of the prostate” (Bjurlin et al., 2018).* This clearer picture sets the foundation for targeting lesions. A high quality MRI allows the prostate and suspicious regions to be accurately registered and annotated. Once rigid and elastic registration is completed, our fusion software fuses the MRI with the ultrasound to create a 3D model of the prostate and lesions. Using the model as a map and the projected needle path as a compass, physicians can easily target regions of interest (ROIs).
*The use of MRI and targeted biopsy should be contingent upon the availability of high quality MRI acquisition and interpretation.8
Tumor locations are easily misclassified as the needle angle is oblique to the posterior surface. Only the site of entry is recorded, even though the needle may sample more than 1 region. Consequently, if prostate cancer is identified, it is unknown whether the lesion is in the apex or mid prostate area.2 Another common occurrence is the oversampling/ undersampling of the prostate as the appearance of cancer is difficult to differentiate from normal tissue on ultrasound imaging.3 Oversampling can lead to detection of clinically insignificant cancers, repeat biopsy and overtreatment, while undersampling can miss clinically significant cancers as a result of sampling the periphery of a tumor with a low Gleason score. This inaccuracy, inherent to TRUS biopsies, has resulted in an undergrading of disease in a considerable proportion of patients. Interestingly, increasing the number of cores marginally increases diagnostic yield. It has not been shown to effectively reduce the risk of undersampling. Instead, it further escalates the potential of identifying small indolent cancers as well as cost. As men are becoming more aware of the realities of overdiagnosis and overtreatment, both physicians and patients are warming up to active surveillance as an option for low risk tumors. Adopting active surveillance as a primary treatment method introduces additional constraints on current biopsy techniques. It requires accurate localization of clinically significant tumors so that they may be regularly and consistently surveyed.1
Fusion biopsies address the issue of sampling reliability which systematic biopsies neglect. By marking up the MRI prior to biopsy, suspicious regions can be identified and visualized in a 3D model. During biopsy, the projected needle path allows the physician to see what area(s) of the prostate are being sampled. Because ROIs are targeted, procedures can be performed using fewer cores, thereby preventing the adverse effects of oversampling/ undersampling. Fusion software also keeps a full record of core locations, so if cancer is accurately located, then the biopsy should be easily repeatable. This reliability makes active surveillance a feasible option for low risk tumors.
Radiology and Urology Go Together
Typically, an abnormal DRE and elevated PSA will warrant a referral by the GP. These screening methods, although useful, aren’t without their respective limitations. The digital rectal exam (DRE) provides a quick assessment of the prostate, but it is limited to the posterior and lateral areas. It can detect palpable abnormalities, but these are typically clinically advanced. By definition, Stage 1 is non palpable. DRE has low sensitivity (51%) and specificity (59%).6 The PSA test has a high false positive rate as elevated levels aren’t always cancer specific. As a result, this ambiguity has blurred the lines between “normal” and “abnormal” levels. At a cutoff of 4.0ng/L, PSA had high sensitivity for any PCa, but low specificity. Any choice of a PSA cutoff involves a tradeoff between sensitivity and specificity.6 Despite these complications, most men are offered a standard TRUS biopsy based on an elevated PSA level or an abnormal DRE.
Magnetic Resonance Imaging (MRI) offers an alternative diagnostic pathway in men with a clinical suspicion of cancer. MRI could be used as a triage test4, 7 to avoid biopsy if the results are negative, whereas positive results could be used for targeting regions of interest during biopsy. Studies like the PRECISION trial4 and PROFUS study7 show that MRIs with or without targeted biopsies resulted in fewer unnecessary biopsies (up to 40%5), a higher detection rate of clinically significant cancers (92.3% vs. 57.7%7), and a decrease in the identification of clinically insignificant cancers (63.4% vs. 82.9%7), all requiring less biopsy cores than a standard TRUS biopsy. Despite the fact that the majority of physicians involved in the trial had modest experience with MRI- targeted biopsies, relative to systematic, the results showed fusion biopsies outperformed standard TRUS biopsies.4
Fusion Biopsy Workflow
Why Fusion Bx?
"Fusion Bx was easily adopted by our clinic. Now, fusion biopsies are a part of our weekly routine."
- Dr. Winston Barzell, 21st Century Oncology, USA
The Fusion Bx addresses three key sources of inaccuracy during biopsy procedures:
- Inconsistent pressure on the prostate can cause deformation which reduces targeting accuracy
- Freehand systems make it difficult to apply consistent pressure
- Focal’s semi-robotic arm helps prevent targeting errors by ensuring consistent pressure on the prostate
- Patient discomfort increases motion
- Focal’s semi-robotic arm allows the probe to pivot at patient’s sphincter for maximum comfort
- Automatic motion compensation can account for minor movements
- Rigid only approach does not account for changes in shape and size of the prostate between image acquisition and biopsy procedure
- Prostate deformation can occur during procedure due to contact with probe
- Focal’s approach combines both rigid and non-rigid (elastic) methods:
- Rigid: Easily identifiable landmarks are used to align images in all three planes
- Non-rigid: A few simple contours are used to automatically segment the entire prostate and deform each slice
Fusion Bx 2.0 is available for sale in the United States, Canada, and Hong Kong
1 Bjurlin MA, & Taneja SS. (2014) Standards for prostate biopsy. Current Opinion in Urology, 24(2), 155-161. doi:10.1097/mou.0000000000000031
2 Wei, JT. (2010) Limitations of a contemporary prostate biopsy: the blind march forward. Urologic Oncology: Seminars and Original Investigations, 28(5), 546-549. doi:10.1016/j.urolonc.2009.12.022
3 Harvey, C.J., Pilcher, J., Richenberg, J., Patel, U., Frauscher, F. (2012) Applications of transrectal ultrasound in prostate cancer. The British Journal of Radiology, 85(Spec Iss 1). doi:10.1259/bjr/56357549
4 Kasivisvanathan, V., Rannikko, A. S., Borghi, M., Panebianco, V., Mynderse, L. A., Vaarala, M. H., . . . Moore, C. M. (2018) MRI-Targeted or Standard Biopsy for Prostate-Cancer Diagnosis. New England Journal of Medicine, 378(19), 1767-1777. doi:10.1056/nejmoa1801993
5 Klaassen, Z. (2018). EAU 2018: The role of multi-parametric MRI as triage test: A propensity-matched comparison of a MRI-triage and a TRUS-biopsy pathway. Retrieved from urotoday.com
6 Hoffman, R. M., MD, MPH. (2018, June 25). Screening for prostate cancer. Retrieved from uptodate.com.
7 Bjurlin, M. A., Rosenkrantz, A. B., & Taneja, S. S. (2017). MRI-fusion biopsy: the contemporary experience. Translational Andrology and Urology, 6(3), 483-489. doi:10.21037/tau.2017.04.30
8 Bjurlin, M. A., Carroll, P. R., Eggener, S., Fulgham, P. F., Pinto, P. A., Rubenstein, J. N., . . . Turkbey, I. B. (2018, October). MRI of the Prostate, Standard Operating Procedure (SOP). Retrieved from auanet.org
9 Weiss, B., & Loeb, S. (2015). MRI/Ultrasound Fusion Biopsy Versus Standard 12-Core Biopsy. Reviews in Urology, 17(2), 113–115. doi:10.3909/riu0670b
10 Cookson, M. S., MD, & Stratton, K. L., MD. (2018, April 10). Point: Is MRI fusion biopsy the new gold standard for diagnosis? Urology Times. Retrieved from urologytimes.com