Sanjay Mehta, M.D.

The most common thing you'd see is skin irritation in that sort of situation, dermatitis and even some chronic flaking and things like that.

The most common thing you'd see is skin irritation in that sort of situation, dermatitis and even some chronic flaking and things like that.

They certainly do because you have to use more energy to get into a larger person. Having said that, there's two different things here because what we normally deal with when I'm talking about dose to a tumor is the dose actually at that spot versus a whole body dose, which is a very different metric.

They certainly do because you have to use more energy to get into a larger person. Having said that, there's two different things here because what we normally deal with when I'm talking about dose to a tumor is the dose actually at that spot versus a whole body dose, which is a very different metric.

And so for someone who I'm treating with, say, eight weeks of radiation for prostate cancer, their prostate may get 80 gray in 1.8 to 2 gray fractions per day, but that's literally only to a small volume, roughly the size of the prostate gland itself.

And so for someone who I'm treating with, say, eight weeks of radiation for prostate cancer, their prostate may get 80 gray in 1.8 to 2 gray fractions per day, but that's literally only to a small volume, roughly the size of the prostate gland itself.

And when you even get just a few millimeters away from that, that dose gets cut in half and then it's exponentially lower because the intensity of the radiation varies with the square of the distance. So as you get even a couple of feet away, that goes down significantly. But typically a patient who is getting 80 grays, if 80 gray was a whole body dose, that would obviously be lethal.

And when you even get just a few millimeters away from that, that dose gets cut in half and then it's exponentially lower because the intensity of the radiation varies with the square of the distance. So as you get even a couple of feet away, that goes down significantly. But typically a patient who is getting 80 grays, if 80 gray was a whole body dose, that would obviously be lethal.

But the whole body dose is more like a few milligray in that sort of situation. So we typically don't see full body sequelae or anything from doing even the heavy duty diagnostic treatment. Now for the CT scan, we almost consider that negligible in our area because again, I'm dealing with mega voltage, high dose cancer killing radiation.

But the whole body dose is more like a few milligray in that sort of situation. So we typically don't see full body sequelae or anything from doing even the heavy duty diagnostic treatment. Now for the CT scan, we almost consider that negligible in our area because again, I'm dealing with mega voltage, high dose cancer killing radiation.

And so when they get a CT scan, which is going to be just a few millisieverts or milligray, that's almost considered rounding error. Versus what they're getting to the tumor area.

And so when they get a CT scan, which is going to be just a few millisieverts or milligray, that's almost considered rounding error. Versus what they're getting to the tumor area.

Normal size person, it's a fraction. It's probably less than one millisievert actually. So it's significantly, it's something that where people who are concerned about things like diagnostic mammograms and all every year, you're still talking about maybe one millisievert or even a little bit less than that with some of the newer machines.

Normal size person, it's a fraction. It's probably less than one millisievert actually. So it's significantly, it's something that where people who are concerned about things like diagnostic mammograms and all every year, you're still talking about maybe one millisievert or even a little bit less than that with some of the newer machines.

You're in a zone where there's a principle we talk about, it's called ALARA, A-L-A-R-A, which is as low as reasonably achievable. And that's been the mantra for our radiation safety people, the Nuclear Regulatory Commission and whatnot, that you want to keep things as low as possible. But having said that, when you're talking about numbers of less than 50 millisieverts,

You're in a zone where there's a principle we talk about, it's called ALARA, A-L-A-R-A, which is as low as reasonably achievable. And that's been the mantra for our radiation safety people, the Nuclear Regulatory Commission and whatnot, that you want to keep things as low as possible. But having said that, when you're talking about numbers of less than 50 millisieverts,

That's kind of an arbitrary number. I should have maybe gotten a test actually when I had my cough last time, but I just don't want to do it. I don't want the exposure. But it's so minimal in terms of biologic effect that we really don't even really worry about those, even if it's getting one of them a month or so.

That's kind of an arbitrary number. I should have maybe gotten a test actually when I had my cough last time, but I just don't want to do it. I don't want the exposure. But it's so minimal in terms of biologic effect that we really don't even really worry about those, even if it's getting one of them a month or so.

And a big reason for that is a lot of these numbers, especially the 50 millisievert number, is extrapolated from higher exposure rates. There's something called a linear no-threshold model, or LNT, and that's been written about extensively, and that's what we're all taught in radiobiology and residency.

And a big reason for that is a lot of these numbers, especially the 50 millisievert number, is extrapolated from higher exposure rates. There's something called a linear no-threshold model, or LNT, and that's been written about extensively, and that's what we're all taught in radiobiology and residency.