Sanjay Mehta, M.D.
speaker
410 appearances
1 recordings
1 series
first heard Apr 2025
last heard Apr 2025
Sanjay Mehta, M.D.’s voice in public audio — every appearance, attributed to the second.
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This is true.
Yeah.
It's one of the youngest fields, too, in that respect. It's not steeped in some of the traditions that surgery and medicine are. So, yeah, it's a new field, highly evolving very rapidly, and the technology has changed so much just in, really, in the last decade or two.
As a kid and growing up in Houston, some of my family friends were radiologists. And I remember just like probably an elementary school kid that some of them were talking about radiotherapy. And these were diagnostic radiologists who at the time, CT scanning was pretty new in the 80s. Prior to that in the 70s and then prior to that, it was kind of just a fellowship.
Radiologists would have a Cobalt 60 machine that they would train on for a few weeks and you do a few easy calculations and do some crude treatments. But it really started, it came into its own starting in the 70s and really more into the 80s. And that's when it became its own discipline. The ACR had a separate carve out. And so our residency training is completely independent of diagnostics now.
So we just do, it's an intern year followed by four years of radiation oncology with a little bit of overlap, but not a lot of diagnostic training at all, just because there's so much to do just on the therapeutic side.
radiation itself, the term itself has got a bit of a negative connotation, but basically it's part of the electromagnetic spectrum. So we have everything on the one in the range of increasing energy of photons, which are just particles of light. On the one end, you have radio waves and microwaves. On the other end, you've got infrared and, excuse me, you've got
ultraviolet and then you get into x-rays and radio waves. And in the middle of all that is the visible spectrum. So when you see, I'm sure everyone's seen the graphs where you've got the rainbow, red, green, blue that we can see, the human eye can only perceive a tiny little narrow spectrum. These are wavelengths.
These are actually wavelengths and energies which are the very low-end energies you have things like radio waves. In that situation, both radio waves and microwaves are what they call non-ionizing. And I know you've talked about this on some of your previous podcasts. I know you had a really good one with Atariwala from Prenuvo. It was a really nice in-depth discussion.
But essentially, the bottom line is that the low-energy stuff that is non-ionizing cannot damage tissue. And that goes all the way up to visible light. Then when you start going to the higher-energy X-rays, that's when you get both X-rays as well as ultraviolet light and then the higher-particle stuff. But basically, the higher you go in the energetics of the particles, the more likely...
exposure to these packets of energy are going to cause damage to your DNA.
Yeah, I'm not sure what the reason is. They are inversely proportional to each other. I don't know that, I guess I'm probably not enough of a physicist to answer that question precisely. But having said that, that is the characteristic of this. And in doing so, that's one of the big reasons why all the fallacies about your cell phone giving you brain cancer and all are just that.
They're fallacies because even having a cell phone on your ear for hours a day, it's non-ionizing radiation. And standing too close to a microwave oven, again, non-ionizing radiation. So that cannot damage your cells.
Correct. It can excite the molecules, but it won't actually eject an electron, which is what would cause an ion to form, which is why it's called ionizing. And that's where we deal with on the, I'm on the therapeutic end. So diagnostic radiologists deal with lower energy x-rays than we do The very high energy X is what we use in our linear accelerators to treat cancer.
So that's the big difference there is kilovoltage versus megavoltage, but all of these are ionizing. Okay.
So radiation dosage, there's a couple of different terms that we've talked about. The main one we talk about when we're talking about patient treatment is the unit called the gray. And that's an SI unit that essentially is joules of energy per kilogram of tissue. So that's what they call absorbed dose. So that's in tissue.
Whereas when you're talking about exposure in the general, in the air and just in general exposure, it's in the air, we usually use the term sievert for that. And actually both those terms for the most part are equivalent. It's just that the sievert itself will take into account if you have different types of x-rays, different qualities of x-rays that have different degrees of
potential to be ionizing, that they have a quality factor you'll multiply it by. But for the most part, we use the term gray when we're talking about, for example, when I treat a prostate patient, they're going to get somewhere between 70 and 80 gray, but it's fractionated into small daily doses as to be tolerable for the body.
And then when we talk about male receivers like we're going to, that's really just a measure of exposure, not absorbed dose in tissue per se.
Yeah, so a gray and a sievert, technically. If anyone's kind of old school, you listen to older stuff, you'll hear the term rads. A lot of people have heard of rads. So one rad is equal to one centigray. 100 rads is a gray. It's just an SI unit versus the old terminology. And a sievert is the equivalent, only it's in air, not in tissue. But a sievert is a gray?
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