So, our next question is—speaking of the side effects—how do the side
effects of beam radiation and brachytherapy compare?
Of course, the side effects of any kind of radiation are partially dependent on the skill and
the quality of the equipment that is being used, and fortunately, in large population centers, most
places are pretty much up to speed in that regard. So, if you just look at equal quality—high-quality
brachytherapy and high-quality IMRT, proton therapy—side effects tend to be similar.
The issue, of course, is the urethra going through the middle of the prostate. So you can get
irritation with urination afterwards. In the past, we used to be concerned with rectal damage and
that's been pretty much solved with the injection of a gel called SpaceOAR between the rectum
and the prostate. So, the rectum doesn't get much radiation anymore with either approach. And so,
I would say that the side effects are similar and so convenience is starting to become a
differentiating factor. So if someone has to go to a facility daily for 6, 7, 8 weeks
versus go for an implant which can be done in one day or perhaps have SBRT where they give treatment
every other day for 5 consecutive treatments—it sounds a lot more attractive,
and the side effects should be very similar with all these different methodologies.
So, what if we compared IMRT and SBRT and then PBRT together? Is it the same?
Yes, I would say as long as you're dealing with experienced doctors that have the right
equipment and have, you know, a good team—a good physicist and good technicians—that
the side effects... I mean, the modern side effect problems with radiation are the development of
erectile dysfunction. I mean, the incidence of lingering urinary problems beyond 6-8 weeks after
treatment is completed is less than 5% now with well-performed radiation, and the rectal issues,
as I already mentioned, have been pretty much fixed. So, it's erectile dysfunction. That's
the big concern, and there's no evidence that the risk of erectile dysfunction from radiation has
any difference between the different delivery methods (proton, IMRT, SBRT, brachytherapy) and
if you look at actual risk, the way we gauge that, let's say for a 60-year-old,
someone who isn't already using Viagra or Cialis,
the chances of erectile dysfunction when you radiate the whole prostate (which
is typically done) is probably about 1 in 3. And we're talking about a type of erectile
dysfunction that does not respond to Viagra or Cialis. So that's sometimes a little confusing.
The rest of the world thinks if you need Viagra or Cialis, then you have erectile dysfunction.
In the prostate cancer world, if you have erectile dysfunction but it responds to Viagra or Cialis,
that's not counted as erectile dysfunction. That's counted as you're "normal." And, yes,
men do function nicely with these pills, but it's a little different methodology for describing what
erectile dysfunction really is, and oftentimes it comes up, "well what do you do then if the pills
stop working?" And that's the seriousness of it. Men have to learn to give themselves injections or
perhaps go for an implanted prosthesis. It's a big deal. And so, whether you do brachytherapy,
SBRT, proton therapy, the risk of erectile dysfunction is the same.
So, our next question is, is there any explanation for why proton beam radiation
does not seem to produce better outcomes than other forms of radiation despite the
selling point that the radiation does not go past the tumor that it is targeting?
Yeah, there's a few misunderstandings with proton therapy. One is I think due to marketing. There's
this implication that they're only treating the tumor and not the whole prostate and that's just
not correct. Whenever radiation is administered to the prostate, they target the borders of
the gland, then they give a homogenous dose of radiation, whether it's proton therapy or IMRT
(which is photon therapy) to the whole gland. I agree with the conclusion of this questioner that
we're not seeing fewer side effects as is often billed the special thing with proton therapy.
The side effects with other types of treatment (IMRT and brachytherapy) are extremely low, so—as
they are with proton therapy—other than the concerns about erectile dysfunction as
we already mentioned. But, I think that it's hard to distinguish between a—you
know, when you have really excellent low risk with all treatments,
it's not surprising that we're not seeing much of a difference between proton therapy and IMRT.
Our next question is in regard to beam radiation. So, is there a preferred form
of radiation for treating the lymph nodes or oligometastatic activity in the bones,
and, if so, which type will work better?
The issues that come up when you're thinking of treating anything is convenience. So,
SBRT which is over a 5-10 day period is certainly more convenient. But, there is some evidence that
the more rapid administration of radiation (which is SBRT rather than over 5, 6, 7 weeks with IMRT)
has greater anti-cancer efficacy, and that is not a real proven fact, but there is some suggestion
that if people are trying to cure bone metastases which is what is going on with oligometastatic
disease, that they might be better served with SBRT. You mentioned IMRT for lymph nodes, and this
is a rapidly evolving area. I think SBRT for lymph nodes, for convenience reasons, is attractive,
but sometimes the lymph nodes are located near sensitive structures like the intestines
and the industry is more comfortable doing IMRT. IMRT has been out for 10-15 years or more now,
and, of course, mistakes in the radiation world are punished severely if some intestine is hit
or a bladder gets hit with the radiation and gets burned. It's just a terrible disaster. So, IMRT or
sometimes proton therapy, which as you pointed out has some special physical characteristics,
are selected in lieu of SBRT. Also, some centers aren't doing SBRT yet, so
doctors are just basically familiar with IMRT. So, SBRT is new. There's a lot of advantages. It has
possibly an increased cancer-killing efficacy on bone metastases. So, all of these methods
are reasonable to consider, but there are certain situations where SBRT might be better.
We're going to be talking—going back to IMRT and SBRT.
Is there a reason for a patient to consider IMRT over SBRT considering the convenience of SBRT,
and would one of the reasons unless microRNA testing would suggest IMRT?
If the doctors that are giving the radiation aren't familiar with SBRT and
don't have the experience, I would definitely go with what they're used to doing. It's never
fun to be in the doctor's early learning curve where mistakes are made. And, other than that,
you know, some of the protocols for combining seed implants with IMRT,
you know, haven't been formalized for giving seed implants with SBRT. So,
perhaps if the person is going to a combination with seed implants plus
beam radiation, there's more experience giving it with IMRT rather than with SBRT.
There are some early protocols that look good giving seed implants with SBRT.
Places such as Memorial Sloan-Kettering or UCLA, but that's not been universally developed yet.
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