Multiparametric MR Imaging of the Prostate after Treatment of Prostate Cancer

Transcription

1 Multiparametric MR Imaging of the Prostate after Treatment of Prostate Cancer RadioGraphics 2018; 38: Pritesh Patel, MD Melvy S. Mathew, MD Igor Trilisky, MD Aytekin Oto, MD, MBA Jeffrey S. Klein, MD Hi. I m Jeff Klein, Editor of Radio- Graphics and today I m pleased to have with us Dr. Pritesh Patel from the University of Chicago Medical Center, Department of Radiology who is the first author of one of our featured papers in the current March 2018 issue of Radio- Graphics. His paper is entitled Multiparametric MR Imaging of Prostate Cancer Following Treatment. Dr. Patel welcome. Pritesh Patel, MD Well thank you very much Dr. Klein. J.S.K. So Pritesh your paper in the current issue deals with a very important topic and it begins with an introduction that discusses the expanding treatment options that we have available for prostate cancer, in particular some of the non-surgical local therapies that are now being employed in selected patients. Can you briefly review for us the spectrum of treatment options that are currently available and touch on why it s important for radiologists to be familiar with the imaging findings, not only after standard surgical and radiation treatments, but also after receiving some of these more novel local therapies for prostate cancer? P.P. Sure, before I begin just on behalf of Dr. Aytekin Oto we d like to thank you again for this opportunity to meet you here at RSNA. J.S.K. Thank you. P.P. So prostate cancer is a little different than most other cancers in that there s a wide spectrum of treatment available. On one end, you have no intervention with active surveillance, or minimal intervention with hormonal therapy; and on the other end you have more aggressive interventions such as surgery, most commonly radical prostatectomy and radiation therapy. In between we have these emerging focal therapies. The focal therapies that are being researched right now include laser ablation, cryoablation, electroporation, photodynamic therapy, and ultrasonic ablation. Now these are increasing in prevalence for example we re part of a multi-center trial dealing with ultrasonic ablation. So given that and the wide variety of treatments available, we really need to know as much about the tumor as we can, and MRI plays a critical role in this. But beyond just knowing how to characterize or diagnose a tumor, each one of these modalities or treatment options can use MRI differently. For example with active surveillance we can use MRI to perhaps prevent frequent biopsies or detect recurrence after a positive PSA but negative biopsies, but more importantly with focal therapies after they are performed, they re really the only way we know to diagnose recurrence because PSA becomes an unreliable biomarker because there s residual prostatic tissue. Therefore, the radiologist really needs to know not only how to diagnose prostate cancer on MRI, but be aware of its role in these treatment options. J.S.K. Absolutely. Well thank you for that. So in your paper after you review the typical MR appearance of prostate cancer, you continue to describe the passive and active approaches to treatment which with the passive approach essentially being as you described active surveillance which so is a little bit of a contradiction in terms, but can you review for us the concept of active surveillance in prostate cancer management? In particular which patients would active surveillance be appropriate for? P.P. Sure yeah so active surveillance at its core is just when a patient has known prostate cancer, but is not no intervention is performed. So the patient is placed instead in a surveillance program. So typically patients who are in active surveillance are of low risk prostate cancer, but what does that exactly mean? What does low risk mean? Well that depends on your institution. So there s a bunch of risk classification guidelines that are out there. The most commonly used one by the European Urologic Association and the American Urologic Association is a three-tiered system of low, intermediate, and high-risk prostate cancer. So a low risk patient for active surveillance is one that has a Gleason score of less than or equal to 6, a PSA of less than or equal to 10, and stage T1C or T2A disease. Now your institution may also employ further criteria such as the Epstein Inclusion Criteria which is the most commonly included one. And that adds tumor volume which is based on the percentage of tumor seen within cores and the number of positive cores that have tumor within them. Unfortunately active surveillance is often misclassified. So 20 to 30 percent are not being put into active surveillance which leads to unnecessary complications down the line such as erectile dysfunction or urinary incontinence. J.S.K. Well that s great so after talking about the active and passive surveillance you begin then to delve into the surgical and radiation treatment options which have sort of been the standard treatment options for people with localized prostate cancer for some time. Let s discuss surgery and then we could look at Figures 3 and 4 which showed both the normal postoperative appearance on MR and Figure 4 which shows an example I think of MR detection of local recurrence of disease. P.P. Sure. Yeah so Figure 3 shows the characteristic find-

2 ings of postsurgical changes after radical prostatectomy. The bladder and the levator sling have descended into the space formerly occupied by the prostate and there s a new vesicle urethral anastomosis. The vesicle urethral anastomosis can have variable signal depending on the fibrosis that s present. Other things to look out for that aren t shown in this image are postsurgical collections commonly abscess, hematoma, lymphocele, or urinoma. Figure 4 shows classic recurrence at the vesicle urethral anastomosis which is similar to the primary tumor low T2, low ADC, early contrast enhancement. This is the most common location, but you should also be checking the antral lateral surgical margin, the space between the bladder and the rectum and in seminal vesicles if they happen to be retained. A couple pitfalls to watch out for are fibrosis and residual prostatic tissue. J.S.K. Right. Well thanks for that. So in detailing the imaging of patients who have received treatment with radiation, you describe a typical post-treatment MR appearance of a decrease in gland size and obviously uniform decrease in you know T2 signal intensity which makes the detection of recurrent disease fairly difficult. Although as you state it s the more common site of disease recurrence is in that area, and this is in distinction to postsurgical recurrence which is most common at the vesicle urethra junction as you have shown us in Figure 4. Your paper then proceeds to discuss the increasing number of local therapies as you mentioned earlier including photodynamic therapy, high-intensity focused ultrasound HIFU, cyroablation, laser treatment and electroporation. Let s take a look at cyroablation which I think it would be good to just review quickly which patients are candidates for cyroablative therapy and then we ll look at Figures 9 and 10 which show two different patients who received cryotherapy and we ll review their findings. P.P. Cyroablation along with the other focal therapies are still developing their role in the treatment paradigm for prostate cancer. However most papers suggest the cyroablation can be used in low-, intermediate-, or high-risk prostate cancer. And sometimes it can be used in salvage therapy after a recurrence after radiation therapy. The cyroablation is when you insert needles into the prosthetic tissue under trans-rectal ultrasound guidance and infuse low temperature gases eventually leading to necrosis of the tissue. Unfortunately there s no consensus as to how much tissue to ablate, so most people end up doing a hemi-ablation trying to spare the neurovascular bundle. So Figure 9 shows your normal appearance after cryotherapy. The first image is an axial T2 image which is showing the very low signal in the left prostate gland and the key here is it also extends through the surrounding pelvic structures. Some of the therapies we talk about later may not do that. Also the part B of the image shows post contrast imaging that has no enhancement in the ablated area compared to the remaining prostate gland and at level C there s a little bit of asymmetry in both peripheral zones and a small amount of fluid in between the peripheral zone and transitional zone. And Figure 10 shows a classic recurrence after cryotherapy. So on one side, on the left side, you have normal postsurgical changes after cryotherapy and you see the recurrence on the right anterior peripheral zone which is low in T2, low in ADC, and not shown but has contrast enhancement here. J.S.K. Alright, great, thank you for that. So let s just move on to talk about laser ablation as a potential therapy. Can you describe how this procedure is performed and why it might be a preferred therapy as compared to the other local treatment options for patients with prostate cancer? P.P. Yeah absolutely. So laser ablation is when you direct a laser beam under MRI guidance to thermally ablate prostatic tissue. So the advantage of focal laser therapy over some of these other ablative measures is that it can be focused and directed since you re using MRI guidance so you can localize it better as well. On top of that, you can use real time temperature monitoring with MR thermometry to really make sure that you re getting an adequate temperature to really ablate those tissues. It s important to note that you want to try to ablate a little bit more than the tumor itself because certain studies have shown that MR may underestimate tumor volume and so that s a good thing to do. J.S.K. And let s look at Figure 11 which I think illustrates a patient who has received laser ablative therapy for their prostate cancer. P.P. Right so Figure 11 shows normal appearance after somebody who has laser ablation like you mentioned. The first image is a pre-treatment image that shows you the biopsy proven cancer in the right peripheral zone and immediately after ablation on the post-contrast image there s a large unenhanced ablation zone which has peripheral rim enhancement which is a characteristic finding of these ablation zones. Three months later you get to see the long-term effects of this as there s architectural distortion, fibrosis, and shift of the volume towards the right particularly the urethra. J.S.K. Great. Thank you for that. So finally, you make an important point in the paper that the role, using the role of dynamic contrast enhanced MR and also in diffusion weighted imaging in particular in the detections of disease recurrence in patients who have undergone treatment. And I think Figure 12 illustrates this nicely. Can we take a look at this particular case which I think demonstrates recurrent disease in a patient who had undergone laser ablative therapy for their prostate cancer? P.P. Yeah you re absolutely right. You know when we have these therapies they tend to mess up our normal sensitivity of T2 weighted sequences given the post-treatment changes such as fibrosis or atrophy and loss of differentiation between the peripheral zone and traditional zone so it s really key to use DCE MR and DWI to really pick out these lesions. This figure is a good example of that. It shows recurrence after focal ablation, focal laser ablation. And what it shows is a really low intensity ablation zone in the left paracentral peripheral zone and there s a new mildly lobulated low T2 biopsy prov-

3 en recurrence in the posterior left peripheral zone. The subsequent DCE image shows focus of contrast enhancement which corresponds to that low T2 signal and also there is incidentally seen in the right peripheral zone another focus of cancer. J.S.K. Great. Well Dr. Patel I want to thank you for taking the time to talk with us today about your paper which is on the MR imaging of patients who have undergone prostate cancer treatment which again appears in the current March 2018 issue of RadioGraphics. P.P. I really appreciate the opportunity. Thank you so much. J.S.K. Thank you.

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