Medical imaging is revolutionising healthcare as technological advances in hardware and software development occur at an astonishing pace. Now, advanced imaging is becoming routine for prostate cancer.
Multiparametric MRI (mp-MRI) provides high quality images of the prostate that allow radiologists and urologists to assign a score, using a 1-5 scale called the prostate imaging-reporting and data system (PI-RADS), to prostate tumours. PI-RADS scores indicate how likely it is that cancer cells will be found if a biopsy is done.
- Scores of 1-2 suggest no cancer cells will be found.
- Scores of 3 mean that cancer cells are likely to be found only 2 or 3 times out of 10.
- Scores of 4 are considered high (a 75% chance of cancer cells).
- Scores of 5 are very high (90-95% likelihood).
These scores help to avoid unnecessary biopsies. In only about 20% of cases (such as in young men with strong family history and strong clinical suspicion) would a biopsy still be recommended for low PI-RADS scores.
For men with higher PI-RADS scores, the MRI images help to identify the sites from which biopsies should be taken.
It is possible to fuse MRI images taken before the biopsy with real-time trans-rectal ultrasound (TRUS) images using software to ensure accurate targeting of biopsies. ‘In-bore’ MRI-guided biopsy is also possible, allowing direct sampling of prostate lesions during the scan.
These techniques are much more accurate than traditional TRUS biopsies, which essentially provided ‘random’ samples of the prostate and resulted in a 30-40% risk of incorrect diagnosis. Now, we can be more confident about diagnosis and management.
Multiparametric MRI helps with treatment by identifying the location of the tumour and its relationship to anatomical structures. Large tumours with very high PI-RADS scores, located close to the outside of the prostate, might have microscopic extensions into surrounding tissues. These are difficult to remove without nerve damage — this is critical for patients deciding how to proceed. Men with tumours away from nerves and blood vessels, or with lower PI-RADS scores, are generally suitable for a nerve sparing surgical approach.
Multiparametric MRI is also useful for monitoring tumours in men with lower risk prostate cancer, who are potential candidates for an “active surveillance” approach (whereby surgery or radiation are avoided).
A Medicare rebate for MRI of the prostate has been available since 1 July 2018, for scans ordered by a urologist, radiation oncologist or medical oncologist (not general practitioners). Specific criteria such as PSA levels, age, DRE findings and risk prior to biopsy must be met to be eligible for the rebate. Men on active surveillance who have not had an MRI are also eligible before a confirmatory biopsy or if there are clinical concerns.