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External vs Internal Radiation Therapy in Prostate Cancer: Patient Selection & Procedure Best Practices
Devante Delbrune • Jul 21, 2022 • 81 hits
Radiation therapy is a common treatment option for patients with prostate cancer. The current methods of therapy utilized by Urologists are generally placed into two distinct categories: internal and external. Urologists Dr. Neil Desai and Dr. Aditya Bagrodia delve further into the distinction between these two categories during their discussion on the BackTable Urology Podcast, covering the role of each therapy in prostate cancer and tips for procedural success. We’ve provided the highlight reel in this article, but you can listen to the full podcast below.
The BackTable Urology Brief
• According to Dr. Desai, internal radiation (brachytherapy) is the more favorable approach for patients with complex anatomy, particularly those with an extremely enlarged prostate. This is primarily based on increased efficacy over external beam monotherapy in the reduction of adjacent structure radiation exposure.
• External radiation can be further broken up into degrees of radiation fractionation. Fractionation relates to the breaking up of a radiation dose. In regards to hypo- vs hyper- vs conventional fractionation, the least effective dosage type is conventional due to increased toxicity.
• Standard practice of care for undergoing external radiation therapy utilizes two phases: (1) Placement of gold markers in the prostate with a SpaceOAR gel to protect adjacent structures such as the anus from external radiation, and (2) CT and MRI guided imaging for the creation of anatomical mold for coordination of radiotherapy guidance.
• The decision to provide external vs. internal radiation therapy according to Dr. Desai should weigh patient-specific factors such as patient anatomy, logistics of treatment, side-effects of treatment and overall efficacy of treatment.
Table of Contents
(1) Internal Radiation Therapy for Prostate Cancer
(2) External Radiation Therapy for Prostate Cancer
(3) Factors to Consider When Determining Radiotherapy Treatment Method
Internal Radiation Therapy for Prostate Cancer
Internal radiation therapy such as brachytherapy is a procedure in which radioactive seeds are implanted into the prostate region of interest. This can be given as a permanent dose in the form of low dose brachytherapy. The procedure is done primarily under general anesthetic in select equipped hospitals. Brachytherapy is often used in the treatment of prostate cancer in patients who have complex anatomy or a very large gland. It may be used as monotherapy or in conjunction with external beam radiation in order to decrease the dose of radiation to adjacent structures by half.
[Dr. Neil Desai]:
So now digging into these spectrum of options. On one end, I would put internal implanted radioactive seeds or brachytherapy, which can be given as permanent radioactive seeds called low dose rate brachytherapy. Or as a temporary seed, which is inserted during a procedure, and then taken out during that procedure, the same time called a high dose rate or temporary radioactive seed in unfavorable intermediate risk, prostate cancer. It is still a matter of debate as to whether you can do those alone. I think there's enough risk for most of these men that you really should consider treating a sort of bigger margin around the prostate capsule, as well as a proximal seminal vesicle at the very least. And so monotherapy with brachytherapy alone is I think debatable and patient to patient. I think for most providers, they would still argue, you need to give most of these men external beam on top of it. So you're combining a lower dose of the brachytherapy seed within the prostate to boost the dose. You can get within the prostate. With supplemental external beam to bound, half dose to treat the prostate periprosthetic areas of the seminal vesicle.
[Dr. Neil Desai]:
That's correct. I think there's solid amounts of data. Now that size, while correlated with urinary symptoms is not the end all be all. If the anatomy is forgiving, and we've had lots of papers now, with every fractionation schedule ration possible externally, at least. That have demonstrated equitable outcomes. Provided the baseline urinary function scores are satisfactory and there's not major obstructive pathology. I think the main caveat would be with brachytherapy or radioactive seed implants just by the very nature of the maybe more invasive nature of the needle placements, as well as the access to the prostate behind the pubic arch made more tough by the enlarged glance. I think there's only so much you can shrink a very, very large gland and still make them a break at therapy. With so many good options. I think the impetus is to make the easy play and pick external radiation, in those cases, as opposed to forcing brachytherapy. And I think most brachy therapists would agree in that regard.
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External Radiation Therapy for Prostate Cancer
External radiation is a procedure in which beams of radiation are aimed directly at a region of the patient's body in order to destroy cancer cells or shrink tumors. There are various dosage modifications for external radiation such as conventional fractionation, hypofractionation and hyperfractionated radiation therapy. Fractionation refers to the dividing of the radiation dosage into smaller or larger individual doses. In simple terms fractionation is the degree with which the beams of radiation are split up. An example of this is hypofractionation, which means the radiation dose is less split up, indicating a larger dose is delivered to the selected region during each individual dose of radiation therapy. In teams of the types of fractionation, conventional fractionation is considered the least effective due to the increased toxicity when compared to hypofractionation.
In regards to the treatment process, Dr. Desai’s practice performs external radiation procedures in two phases. The first appointment is performed in clinic where they place gold markers for fiducials in the prostate and a SpaceOAR gel to protect the rectum from prostate radiation The second appointment they have their patients undergo CT and MRI imaging which they make a mold of. The molds are used to determine the angles of approach for radiation therapy. He states this is the standard of care to best minimize radiation to structures adjacent to the prostate.
[Dr. Neil Desai]:
It's been well-proven over many, many years with long-term results, good outcomes. They pin down the actual doses that get best outcomes and exactly what trade-off of side effects. Furthermore, the delivery of radiation with conventional fractionation is considered to be failure robust across almost every practice setting, and every kind of image guidance for how you actually track the prostate. So very forgiving in this regard to baseline urinary features to practice types and expertise, or comfort level, I should say, not expertise, but different people will have different comfort levels with different fractions. With that said, there are now multiple bars trials that have been well conducted and shown that with better technology and better targeting of image guides in particular, we can deliver a higher dose per day or hypo-fractionation, meaning fewer fractions, higher dose, which can be done moderately meaning slightly higher dose per day. So over 20 to 28 days, for instance, or many different regimens. I like 20 days if I'm doing this. And that's equitable in terms of, outcome as well as side effect profiles. Again, the main difference being a little bit higher, acute urinary symptoms in most studies. And then now we even have ultra hyper-fractionation, which classically refers to five day and is what we define the United States at least
[Dr. Neil Desai]:
Yeah. I always say, look for external radiation options, you're always gonna have two preparatory visits. One is for the procedure which we do under minimal sedation in our clinic in the ambulatory setting to place the gold markers for fiducials in the prostate, as well as the spacer gel between the prostate and rectum. Then you come back about five days later for your mapping scans or simulation, which are the second preparatory appointments, we always do a CT and MRI. We make a mold for the patient, so it conforms to the body replicating the same position, and perineal pressure, for instance, which can affect prostate position and stability. We have them do various maneuvers to minimize radiation dose to the bladder and rectum, for instance, having to have a comfortably full bladder to push the bladder wall away from the prostate, as well as have the empty rectum, such that there's less motion of the prostate.
We then do that mapping scan. We delineate the prostate and they come back for radiation roughly about a week later. If you're doing five day radiation, you're going to do that twice a week for two and a half. If you do 20 day radiation, you're gonna do that five times a week for four weeks. And if you do the 44 day radiation or conventional radiation. You're going to do that multi-nine week radiation almost daily. Now how long you're in department, each of these days for treatment. Roughly the longest are these five day radiation appointments, which are much more precise and demanding of our setup. And those days are probably around 45 minutes plus for the patient. For the shorter course rate or long course, radiation with a little lower dose per day and less exacting requirements, there'll be in and out roughly that 30 to 40 minutes.
Factors to Consider When Determining Radiotherapy Treatment Method
The two types of radiation therapy are not shown to be statistically different in metastasis rates of cancer following treatment. The major differences and what the biggest considerations are when determining a treatment regimen are the side effects along with the logistics of the treatment. Brachytherapy combination therapy has been shown to have more acute symptoms such as strictures when compared to external beam therapy alone. On the logistical end Internal radiation is not available at every facility due to the specific expertise of it along with the consideration that internal radiation therapy requires anesthesia. Another consideration in decision making is the patient variability. If a patient doesn’t fit typical criteria it is difficult to determine the efficacy of treatment for external radiation. The two radiation treatments are often combined to decrease the dose of radiation required per treatment. Dr. Desai states there is a solid argument that external radiation utilizing models can be equally if not more effective than brachytherapy alone but that is on a patient to patient scale.
[Dr. Neil Desai]:
So it's controversial, but that is an option that is considered an intensified approach with higher biochemical control by about 10-15% of historical trials, but no difference in survival metastasis. So again, you're trading long-term control and sleeping well at night that your PSA is not going to come back, but for a higher risk of urinary injury in particular was the historical trade off. And that's, there's still something to read as true.
[Dr. Neil Desai]:
I think the main thing that the trade off side effect wise, the late injury risk for strictures, and urinary injury such as cystitis is higher, in the combination brachytherapy boost group. At least based on historical data. And you can criticize that data, that a lot written about this, that perhaps those rates were overstated because they're like 20 year ago therapy. But I think yes modern contemporary series show a lower toxicity rate, late grade three urinary events. But they are still slightly higher than the external beam alone. And that's the trade-off I think probably even more so important than the acute phase alone.
[Dr. Aditya Bagrodia]:
Yeah, and I think there's certainly some truth to it that going in and handling the outlet in somebody that's received, low dose rate seed implants can be a fairly hectic affair for the patient, with incontinence, a significant lower urinary tract symptoms. And then you'd kind of alluded to this earlier. This is going to be institution specific, right? I mean, in many places brachytherapy is kind of considered a dying art where it's not necessarily even propagated to the next level. Is that fair?
[Dr. Neil Desai]:
Yeah. so I mean, everyone, everyone likes what they do best and brachytherapy and expertise, or at least a skill set that is not everywhere. It requires more logistics. There's controversy over whether the benefits as biochemically are worth it from the side effects standpoint, and the less you do, the worse you get in terms of your outcomes certainly. And so I think a lot of providers would favor external beam alone. And I think the good part of all of this is that there really are a lot of options at this juncture that kind of spread the benefits of each approach across the continuum, more so than it used to be. So it used to be, if you wanted the best control you got brachytherapy boost and that was it. Okay. Are we though now with MRI based lesion targeting as an enlarged phase three randomized trial that was published last year showed? You're getting similar benefits in biochemical control. Again, with these MRI guarded, external beam alone approaches that may be a rival brachytherapy boost.
And so the biggest thing to brachytherapy boost is it's great if you can do it and it's great that you like it, but what if your center doesn’t offer it? What if the patient's prostate is too big? What if they had obstructive urinary symptoms that are beyond AUA IPSS score of 15, which has traditionally been a relative contraindication to brachytherapy? Not everyone can get this quote unquote gold standard. So what kind of gold is it exactly for those men? And so I don't think it's a great stance nowadays to say that only one approach is the best. I think for that patient, if they have perfect urinary symptoms and want the most aggressive control, certainly brachytherapy boost is a very attractive option for them. But you're not losing out nowadays with the other approaches either.
Dr. Neil Desai
Dr. Neil Desai is a radiation oncologist with UT Southwestern in Dallas, Texas.
Dr. Aditya Bagrodia
Dr. Aditya Bagrodia is an associate professor of urology and genitourinary oncology team leader at UC San Diego Health in California and adjunct professor of urology at UT Southwestern.
Cite This Podcast
BackTable, LLC (Producer). (2022, June 1). Ep. 41 – Radiotherapy for Unfavorable Intermediate Prostate Cancer [Audio podcast]. Retrieved from https://www.backtable.com
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