Video: Clinical Trial: SBRT vs IMRT For Low Risk to Intermediate-Risk Prostate Cancer

Clinical Trials | Transcription

Hi, I'm Dr. Scholz. Let's talk about clinical trials for prostate cancer.

In the trial that we're going to look at today, we're gonna look at what is better for men with Low-Teal (that's intermediate-risk prostate cancer) in the comparison between SBRT (stereotactic body radiation therapy) and IMRT (intensity-modulated radiation therapy). SBRT and IMRT are very similar in the sense that both are a form of beam radiation to zap the prostate; however, SBRT is given is less than two weeks and the IMRT protocol that they're looking at is given over five weeks. Many of you have probably had IMRT and it took nine weeks. Well, it appears that five weeks is just as good based on previous clinical trials. So they're comparing the five-week protocol with, we'll call it the two-week protocol, or SBRT. Interesting things about this trial is that when you try and answer a question like this in low (relatively low) risk prostate cancer. First of all, it's designed to run to 2030. 11 years from now because that's how long it takes for these Low-Teal patients to play out their story of relapse and whatnot. Most of these people are going to be cured with either approach. In fact, it's possible we could ask if this is even wasted money considering that you're getting such great results with either approach. There's a difference in convenience, certainly, by getting it in two weeks rather than five weeks, but the unanswered questions are "Is there any difference in cure rates?" Is there any difference in the side effect profile? And that's one of the strengths of the study running for such a long period because sometimes the side effects from radiation can be delayed for a number of years. That really is the question because we know the cure rates are going to be great with this group of prostate cancer patients who are so low-risk.

So, specifically in the trial, we're talking about men with High-Sky and Low and Basic-Teal. So that's defined as men with either Gleason 6 and a PSA over 10, or men with Gleason 3+4 and a PSA under 10 and no biopsy cores more than 50% replaced with cancer. We're looking at a really favorable group, a very uniform group, and this is going to then allow them to discard the use of any hormone therapy. So it's just pure radiation for these very low-risk patients. Of course, I'm concerned that the High-Sky and the Low-Teal patients, some of these patients could be safely monitored with active surveillance and the radiation could be overtreatment, but I'm not here to criticize the types of patients they're treating—just to inform and help you all understand what's sort of the cutting edge in terms of modern radiation therapy for prostate cancer and I think it really does come down to this five-week protocol versus the two-week protocol. My own concerns with this shorter protocol, but familiarity with this approach over the last five years has been a slightly increased risk of rectal burns, but now that SpaceOAR has come on the market—a gel that's injected between the prostate and the rectal wall, the risk of rectal burns has been vastly reduced if not eliminated and therefore convenience would seem to be the overriding issue. There are a number of studies taking SBRT, the two-week protocol, out four and five years and we're not seeing any early signs of bad side effects in a semi-delayed sense. So, at this point, if it was me, I'd probably be thinking of SBRT.

A couple of other interesting aspects of this study. Everyone is going to be required to get a multiparametric MRI and they're going to look at the MRI findings and see if those are helpful in predicting future relapse rates. This makes a lot of sense. We at the PCRI have been advocating a shift from random biopsy staging to MRI staging for a long time, and the NCI is clearly picking up on that thinking. The other thing that is relevant to this is that they won't allow anyone into this trial that has more than a 60cc prostate. 40cc is the mean for men in this age group. 60cc means about 50% bigger than average. These are not tremendously large prostates. The issue is with radiation when treating a larger prostate a bigger field is required and you're going to have to give larger amounts of radiation and in all probability incur a higher risk of side effects. So, one of the things in these trials is always to ensure uniformity of the treatment groups so that if there are differences between the different types of radiation, it's due to that and not due to other unexpected factors.

So, the NCI is spending millions of dollars to sponsor a study looking at a comparison between very short term radiation versus what we'd call intermediate-term or a five-week radiation. This is a reasonably important question, but we're not going to have the answer for a long long time. Patients, today, that don't want to participate in a trial can honestly consider either option because it would be unethical for them to include these different types of treatment if they didn't think that they could sell it to a board that reviews all these things. But, if you want to help participate in the answering of this question, there are almost 200 centers being sponsored by the NCI around the country right now that are recruiting people for this project. So if you're interested in participating in this trial, I think that it's a reasonable trial to participate in and you can talk to your radiation therapist about some of the different resources and methods to get involved. Also, we'll be providing some information on the screen.