0:00

So let's examine some of what is there when I mean risk

0:05

for high skin doses. When I say that, I also want to discuss

0:09

what is called the biological effect of radiation.

0:12

The biological effect of radiation can be broadly

0:15

categorized into two categories.

0:18

One is called the stochastic effect, the other one is called the

0:22

non-stochastic effect, also known as deterministic

0:25

effect or tissue effect. The first one

0:29

is pretty much straightforward. The difficulty with the first stochastic

0:33

effect is very difficult to quantify because it's more

0:36

probabilistic in nature, and you don't see this

0:40

effect immediately. You can see this effect three to 20 years later,

0:44

such as radiation-induced cancer in exposed individuals,

0:48

mutations in offspring of exposed individuals, and so forth.

0:52

That is the common risk we have associated with any radiation

0:56

exposure across the board, and that too with medical X-ray imaging.

1:01

The area which of interest, especially with the interventional fluoroscopy

1:05

procedure or the non-stochastic effect, also called as

1:09

deterministic effect. These occur due to direct damage

1:13

to tissue due to local cell death, and the

1:17

characteristic of deterministic effect is they are quantifiable

1:21

and they are observed within days to weeks.

1:23

Let me show you an example. Here is a table showing, on the

1:27

left-hand side, the type of skin injuries

1:31

and the threshold dose it requires to cause this

1:34

injury, and the third column tells what's the onset

1:38

time.

1:39

On the right-hand side is a classic image published about a patient

1:43

undergoing a coronary angioplasty procedure.

1:46

After a few weeks, the injury starts showing up, and

1:50

it goes away, and it resurfaces back

1:54

because basically the understanding here is during this phase, the

1:58

skin was trying to repair itself and trying to come back to the original

2:02

state, but it lost its fighting and basically created a

2:05

necrosis, and the patient had to go through a skin grafting.

2:09

You look back to the left-hand side, here are the injuries and the

2:13

threshold dose to skin injuries. This is expressed in

2:17

Gray. Gray is a unit of absorbed dose.

2:20

It is a large quantity. We typically see milligray doses

2:24

in imaging. But here, if a procedure with the same skin

2:28

surface or a hair area received more than two gray

2:32

or three gray, that is in conventional unit is 200 rad or

2:36

300 rad, that can set up an early transient

2:40

erythema.

2:41

If it is more than six gray, it's a main erythema.

2:43

The person will definitely have a permanent injury.

2:47

Severity of the injury increases with the total dose accumulation in the skin,

2:51

and in this comparison to this figure, this necrosis may

2:55

have caused because of the radiation exposure greater than

2:59

18 gray.

3:01

As you can also see here, less than one week to three weeks, they're much

3:04

more quantifiable, and that's one of the reasons these days

3:09

most fluoroscopy procedures, especially interventional fluoroscopy procedures,

3:13

we track the patient dose so that if the patient dose is quite

3:17

high, we can alert the patient to watch out for this type of injury.

3:21

Skin burns are rare but possible. The reason why I state this

3:25

statement is in the US, we do approximately about 11

3:29

million interventional procedures on an annual basis, and we

3:33

see only a handful of injuries. And that we

3:37

assign it because of the technological advances and the awareness

3:41

of radiation procedures and understanding the radiation protection principle.

3:45

The same thing applies for anybody getting into the field of

3:48

fluoroscopy to understand these things.

3:52

So here are some injuries which may have caused because of

3:56

the interventional fluoroscopy, and this was published back in 2001,

4:00

and the injury of a person undergoing a coronary angioplasty procedure

4:04

has resulted in a skin injury. And with the

4:07

explanation given in the article is there was a repeat procedure

4:11

done, and with the repeat procedure, the same skin surface

4:15

was overexposed, overlapped, and which received a dose

4:19

greater than the threshold causing this injury.

4:23

Then there are other examples which could be avoided.

4:26

Here's an example of a patient with the elbow

4:30

sticking out, and I don't know, probably it's too close to the X-ray tube

4:34

causing this injury.

4:35

And the same thing here, the female breast getting a permanent

4:39

scar because it was closer to the X-ray tube side.

4:43

Most of these can be avoided by what I'm

4:47

going to explain as we go along with this part of this lecture.

4:52

To understand skin injury, the tissues at risk for radiation

4:55

injuries are the following: skin, hair, subcutaneous fat,

4:59

and muscle. So they are much more sensitive.

5:02

They have higher risk for causing cancer.

5:04

That's why neurointerventional procedure, if it is done for a long time in

5:08

the same location, you can have hair loss or in the

5:12

cardiac procedure or interventional procedures, if the skin

5:16

surface received greater than the dose, two gray or three gray

5:20

is considered as a threshold dose for causing the skin injury.

5:24

Now,

5:25

the radiation injury, what are the factors which influence radiation

5:29

injury? The expression and the severity depends on the

5:33

following things. One is straightforward, the radiation dose.

5:37

The greater the radiation dose to the same surface, the greater the chances for

5:41

radiation injury.

5:43

Then the second is interval between irradiation.

5:46

This we call as dose fractionation.

5:48

What it basically says, a lot of the interventional procedures, the physician

5:52

brings back the patient for repeating some procedures.

5:56

If you can keep the time interval between the two procedures, that will

6:00

reduce the chances for injury because the skin would have replaced the

6:04

tissue. The cells would have repaired itself.

6:07

The size of the skin area irradiated is also important.

6:11

That's why we try to collimate to the area of interest, not expose

6:15

areas which doesn't have to be exposed.

6:18

There are other factors such as physical and patient-related factors,

6:22

especially physical and patient-related factors such as obesity,

6:26

a person who's smoking have a higher chance for radiation injuries

6:30

for the same dose.

6:32

There are also intrinsic factors.

6:34

The timing of expression depends on these things, and also the

6:38

dose threshold can be low for a sensitive patient compared to an

6:42

average patient. So in general, for an average patient,

6:46

the threshold for causing skin injury is about two to three

6:50

grays. Two to three grays is 2,000 to 3,000

6:54

milligray entrance skin dose, and that's what we care, we

6:58

track on the patient when we're doing this interventional procedure.