Radiation Therapy for Prostate Cancer
Dec. 15, 2008 — Radiation therapy is a common complement or even alternative to surgery for prostate cancer patients. Jeff Michalski, MD, explains the two most common courses of radiation therapy for prostate cancer, discussing the application of each and their side effects. Michalski also explains how a new system to track even slight movements of the prostate gland during treatment is benefitting patients.
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Transcript of Audio File
On this edition of Cancer Connection, we’ll talk about radiation therapy for prostate cancer, who’s a candidate and what new technologies are on the horizon.
Host: Thanks for downloading this podcast from the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine in St Louis. I’m Jason Merrill. Depending on the stage of diagnosis, many men may opt for radiation therapy to treat their prostate cancer. To talk with us Jeff Michalski. Dr. Michalski is interim chair of radiation oncology at the Siteman Center Cancer Center. Dr Michalski, thank you for joining us.
Michalski: I’m happy to be here. I’m looking forward to sharing with you some of the new things we have going on at the Siteman Cancer Center and specifically our department of radiation oncology here at Washington University.
Host: What type of prostate cancer patient needs radiation therapy?
Michalski: Most patients who are diagnosed with early stage prostate cancer are candidates for radiation therapy. In fact, most patients today with early stage disease have an option to choose from surgery or radiation therapy, and in most cases their prognosis is going to be the same whether they choose radiation therapy or surgery.
However, when patients develop more aggressive forms of prostate cancer, in those cases, surgery may not be the best choice of treatment for them, and radiation therapy is often the preferred method of treatment, especially when they have high-grade disease or advanced clinical stage and they might require not just radiation therapy but also a combination of radiation therapy plus hormones. Furthermore, patients who are of advanced age yet still have a long prognosis might be better suited for radiation therapy over surgery because a man who’s 70 years or older is less likely to recover from an operation such as radical prostatectomy as well as a younger man. So those patients are often referred for radiation therapy as a preferred treatment over surgery.
Host: There are two basic types of radiation therapy: external-beam radiation and brachytherapy. Talk about the differences in the two types of approaches.
Michalski: External-beam radiation therapy, as the name implies, is treatment delivered with an external radiation source. Basically the patient comes in for treatment daily, Monday through Friday, five days a week, for a course of therapy that could stretch on as long as eight to eight and a half weeks. The treatment requires that they lie still on a treatment table, and the linear accelerator, the machine that delivers the external-beam radiation therapy, will move around them delivering radiation therapy at different angles.
Brachytherapy, on the other hand, is a treatment that involves the implantation of radioactive substances into the patient. These are typically small seeds made of iodine 125 or palladium 103. These are isotopes that are used to treat prostate cancer, and these are placed directly into the prostate under both ultrasound and X-ray guidance. The brachytherapy, of course, because it is an invasive procedure, does require some sort of anesthesia. So the patient may be in the operating room for an hour to an hour and a half, and this is done, like I said, under anesthesia. Once the procedure is done, the patient wakes up, and there will be a catheter in their bladder. We’ll make sure there’s no problem with bleeding or other complications, and the patient will be sent to our department for some additional X-rays. Typically, the patient will go home the same day as the procedure. This generally does not require an overnight stay or hospital admission.
Host: With brachytherapy, there are radioactive seeds, correct?
Michalski: Yes, brachytherapy involves the placement of radioactive sources directly into a tumor or, in this case, into the prostate gland. These sources can vary depending on the manufacturer or position preference. Typically, the isotopes that we use are iodine 125 or palladium 103. These are implanted and stay in the gland permanently, but the radioactivity actually decays over a period of weeks or months. In the case of iodine 125, the half-life of that isotope is 60 days. So over about three half-lives – or about six months – the treatment is effectively delivered. If we were to use Palladium 103, the half-life is just 17 days, so the treatment delivery is over a period of just six to seven weeks.
Now the side effects of treatment from this therapy can stretch on for a few weeks or even a few months after the implantation of the isotope, so patients have to be prepared for the possibility of some mild to moderate urinary frequency, especially at night, and sometimes a stinging or burning sensation when they urinate. But generally, after about six months or so, these side effects start to settle down, and patients start to feel much more comfortable.
Host: How do you determine which patient gets external-beam therapy and which patient gets brachytherapy?
Michalski: Oftentimes it’s a choice that the patient needs to make for himself. What I generally do is counsel patients about the various types of side effects that they might experience as a result of treatment. In some cases, the choice is clear. For example, a patient who has a lot of urinary obstructive symptoms or who has a very large prostate may not be the ideal candidate for brachytherapy, and in that case, I steer them toward treatment with external-beam radiation therapy. But quite honestly, most patients, they have the ability to make the choice for themselves, and what I generally counsel them is how the various treatments might impact their quality of life.
For external-beam radiation therapy, there often is very little change in terms of their sexual function and mild changes with respect to their urinary function. Brachytherapy also causes very little immediate disruption of the patient’s sexual function; however, they may be bothered by some of the obstructive or irritative symptoms that accompany the placement of radioactive sources into the prostate. These patients might complain of more urinary stinging and of more urinary frequency, but generally this takes place only for six months or so. So patients who want to avoid irritative symptoms or getting up at night to urinate frequently might decide to avoid prostate brachytherapy.
On the other hand, external-beam radiation therapy appears to have slightly more increased bowel irritation. So a patient who’s worried about symptoms of bowel frequency or symptoms of hemorrhoidlike irritation might try to avoid external-beam radiation therapy. The fact of the matter is that at about a year’s time after treatment, the long-term sequellae or side effects of treatment are pretty comparable between the two modalities.
Host: There are a lot of new technologies for radiation oncologists such as yourself, and one of those is called Calypso. What does that system do?
Michalski: Well, Calypso is a new radiation therapy localization system. We learned long ago that the prostate is actually a quite mobile organ. During a course of treatment and sometimes even during a single treatment of radiation therapy, the prostate can move as much as a centimeter. The reason the prostate moves is the rectum can fill with gas or stool. Or urine, as it fills the bladder, will put pressure on the prostate, causing it to change its position. And also, sometimes the patient himself might be a little tense, especially early on during the treatment course, nervous about what might happen with the daily treatments, but then becomes more relaxed. So all these things have some effect on the pressure and tenseness of the muscles around the prostate, and as the patient relaxes or as these organs change in their distention with either stool or urine, the prostate will move about.
So what we started doing years ago was using systems that help us focus the radiation beam on the day of treatment. We initially started with an ultrasound – by taking an ultrasound picture of the prostate – but we found that actually was a little bit cumbersome. It required some interpretation on the part of the therapists to know if they were seeing the prostate clearly. So then we moved to placing gold markers into the prostate, and we still use gold markers today. They’re actually very useful in helping us localize the prostate. These gold markers – and also the Calypso system – these are placed into the prostate, sometimes under a local anesthetic. We then use these markers to take pictures of the prostate with an X-ray beam. Then we'll adjust the patient’s position to make sure we’re hitting the prostate each and every day.
Calypso and its localization system allow us to take this one step further. As I said, even during the treatment, a patient or his prostate might move a bit, and the gold markers only allow us to see the position at the beginning of the patient’s treatment. Calypso, on the other hand, allows us to determine the localization of the prostate during the entire 15- to 20-minute treatment session. What happens is this Calypso marker is actually a small little transponder that responds to radio frequency just like a radio might. In the room, we have radios and cameras that will emit a signal to the Calypso beacons, which are placed inside a patient’s prostate. And then the Calypso beacons echo in response, telling us basically where the prostate’s position actually is. So not only does this help set the patient up before treatment begins, but as the treatment occurs, the therapist outside the room can monitor the actual position of the prostate within just a millimeter or so. If they see that the patient’s prostate has moved beyond a preset distance of just a few millimeters, they will interrupt the treatment and wait to see if the patient’s prostate resumes and falls back into its original position. If that doesn’t occur, they can stop the treatment, readjust the patient’s position and then resume the treatment once we know for sure that the patient’s prostate is exactly where we need it to be.
What we’ve learned is that about 35 percent of the time, the prostate’s position can move more than 3 millimeters. And about 17 percent of the time, it can move more than 5 millimeters. These are distances that might seem small, but they mean quite a bit when you’re treating prostate cancer and you risk missing the disease with your radiation beam.
Host: So what are the benefits for a patient?
Michalski: So generally when we approach a radiation plan, we put around the prostate a margin of uncertainty that allows us to reassure ourselves that on a day-to-day basis we’re hitting our target with the X-ray beam. That margin has to be bigger if we are unable to know with great precision where the prostate is on a day-to-day basis or, for that matter, on a second-to-second basis. So what these technologies like the gold markers and even more so the Calypso system allow us to do is reduce the margin of error. And for every millimeter that we reduce the margin of error, that translates into a significant volume of tissue that would otherwise be irradiated that does not need to be irradiated. So by shrinking that margin of uncertainty, shrinking that margin for error, we can spare more of the patient’s bladder and more of their rectum, which will result in better tolerance for the patient.
Host: What do you see in the future for radiation therapy for prostate cancer?
Michalski: Well, I think some of the new technologies for localization, such as Calypso, will allow us to explore shorter and shorter treatment times for our patients. What we’ve learned is that prostate cancer doesn’t behave like many other cancers with respect to its response to radiation. Most cancers require a long course of radiation – just as we are doing now with prostate cancer – seven or eight weeks long. However, what might actually be more beneficial to the patient who has prostate cancer is to compress this treatment time into a matter of just a few weeks. Now we’ve not been able to do that with our older technologies because by compressing the treatment time, if you were at the same time treating large volumes, the risk of side effects or toxicity would be significant. So what we’re finding is that with the smaller margins and more precise delivery of radiation therapy, we can more safely reduce the overall treatment time from a typical course of eight and a half weeks to something like five and a half weeks.
Currently, we’re doing a randomized clinical trial of patients with low-risk prostate cancer. Those are patients who have a PSA of less than 10, a Gleason score of 6 or less and a normal-feeling prostate. Those patients with low-risk disease can be randomized to receive either the short course with daily localization or the more traditional course of radiation of eight and a half weeks. That traditional course of radiation also includes the daily localization. We believe that the short course will not only be more convenient but potentially more effective than some of the radiation biology models would suggest.
Host: Dr. Michalski, thank you for joining us.
Michalski: It’s been my pleasure. I look forward to helping patients who confront this disease in the future with some of this new technology.
Host: For more information about radiation oncology, you can visit the Siteman Cancer Center online at www.siteman.wustl.edu or call 800-600-3606. Thanks for downloading. Until next time, I’m Jason Merrill.