Written by Dr Eamonn McAteer & Dr David Homewood, Radiologists and Partners, South Coast Radiology.
Prostate cancer has become the most significant major malignancy of Australian men (30% of cancers in males) and is responsible for 3,300 deaths annually. Around 20,000 new cases are diagnosed every year, yet diagnosing this condition still presents a challenge.
Prostate cancer diagnosis via imaging has remained elusive even though pre-operative MRI staging of biopsy proven adenocarcinoma has been available for some time (since 2003 on the Gold Coast). Fortunately, recent MRI technological advances and considerable international research have established a new imaging protocol for diagnostic prostate cancer imaging. South Coast Radiology is pleased to offer this multiparametric MRI (mpMRI) prostate imaging service on the state-of-the-art, high field strength 3.0T MRI at Pindara South Coast Radiology.
Current diagnostic testing for prostate cancer
Currently, screening for prostatic adenocarcinoma is based on two tests; digital rectal examination (DRE) and prostate-specific antigen (PSA). If either of these are abnormal, a transrectal ultrasound (TRUS) guided biopsy is often the next step and prostate cancer diagnosis is typically made through TRUS-guided sextant biopsy and histopathological examination. However, each of these tests has limitations – DRE has low overall sensitivity (50%), and PSA measurement has higher detection rates but the specificity is low (40%), from false-positive PSA elevation under benign circumstances. TRUS biopsy also has limitations (false negative 15-30%) as random biopsy sampling can miss the tumour entirely, or the most aggressive part.
Urologists also often face the dilemma of managing patients who have a high degree of suspicion for cancer (based upon PSA/DRE) and a pathological diagnosis cannot be confirmed. In these patients mpMRI can help as it has the potential to identify suspicious areas within the prostate so that TRUS biopsy can be targeted to this zone.
What is Multiparametric MRI (mpMRI)?
A Multiparametric approach simply means assessing the prostate by more than one MRI imaging method to provide both morphological and functional information. The most common mpMRI protocol includes assessing the anatomy and morphology of the gland on T2, the cellular characteristics by Diffusion Weighted sequences, and the vascular characteristics by Dynamic Contrast Enhancement. The combination of these three techniques and the fusion of images from the various data sets greatly assists sensitivity and specificity. mpMRI can detect and localise tumours with 90% accuracy.
T2-weighted images have high spatial resolution and provide structural information. On T2-weighted images, prostate cancer usually appears as an area of low signal intensity within the high signal intensity of the peripheral zone. A limitation of T2-weighted imaging is that focal areas of low signal intensity in the peripheral zone do not always represent cancer. Benign abnormalities such as chronic prostatitis, atrophy, scars, radiotherapy or hormonal treatment effects, hyperplasia, and post-biopsy haemorrhage may mimic tumor tissue.
Dynamic contrast enhancement (DCE)
Angiogenesis in prostate cancer and resultant changes in vascular characteristics can be studied well with dynamic contrast-enhanced MR imaging. Sites of prostate cancer typically show earlier, more intense enhancement and earlier, more rapid contrast washout compared with normal prostate tissue. The dynamic enhancement data is carefully assessed to find the typical pharmacokinetics of cancerous tissue. One of the limitations of DCE is discrimination of cancer from prostatitis and from highly vascular BPH nodules.
Diffusion weighted (DW)
In DW imaging, micro-movements of water are examined within the prostate gland – tumour cells demonstrate restricted movement whereas in normal tissues the movement is more free. DW images have been shown to correlate with the cellular density of prostate cancer and is useful is characterising tumour aggressiveness. DW imaging is particularly helpful in detection of recurrent disease post radiation therapy or surgery in patients with increasing PSA levels.
Current and future potential uses for mpMRI
mpMRI of the prostate has the potential to fulfil multiple roles in regard to prostate cancer, including:
-Improving diagnostic accuracy
-Post-op follow-up for cancer recurrence
-Characterisation of prostatic tissue
-and more recently, guidance for targeted biopsy
As Radiologists we recognise that management of patients with suspicion of prostate cancer can be very complex and we want to provide mpMRI on correctly selected patients for specific outcomes. South Coast Radiology will continue to work closely with local Urologists to ensure that the examination is useful in assisting patient management. As such we will only be providing mpMRI prostate from a Urologist’s referral.
mpMRI can also be helpful to the Urologists who are managing patients under active surveillance protocols. These are patients who are considered low-risk, but need to be monitored for detection of cancer progression.
Detection and management of prostate cancer remains challenging. International research has shown that mpMRI can assist both diagnosis and staging. The three main questions we are trying to answer for the Urologist and Radiation Oncologist are:
1. Is there prostate cancer?
2. Where is it?
3. What is the stage of the disease?
We need to continue to work with Gold Coast Urologists like Charles to ensure that the technique is accurate and reliable and that imaging diagnosis correlates well with pathology and surgical findings. The potential benefits of mpMRI are far reaching due to the high incidence of disease and the many management options for each patient. Our MR prostate Radiologists are hopeful that mpMRI of the prostate using current and future techniques will prove to be increasingly helpful in managing patients with prostate disease.