0:01

So there are several patient dose reduction

0:03

strategies.

0:06

One is to minimize the time of exposure.

0:09

If we are not examining, if we're not doing anything, we should

0:13

not unnecessarily expose the patient by keeping what is called as

0:17

lead foot syndrome. Because the fluoroscopy

0:20

systems are operated having a leg switch, a switch at the leg, and

0:24

if somebody stands on the switch, the fluoroscopy keep going.

0:27

It's very quiet, so nobody knows that.

0:30

And that's why we try to tell, like, we need to take the foot away

0:34

whenever there is no

0:36

need for viewing the patient or any so forth.

0:40

Collimation, use the pulse fluoroscopy is a very important one.

0:45

These days, the technology has improved, and it is

0:48

routinely done as 15 frame per second or

0:52

even seven and a half frame per second to minimize the patient

0:56

dose as such.

0:58

To minimize the use of magnification is another factor discussed

1:02

earlier regarding how the magnification can increase the

1:06

patient dose, and also maximize the distance between the

1:09

X-ray source and patient,

1:12

and minimize the distance between patient and image receptor.

1:15

These are some of the strategies anyone can need to

1:18

utilize to minimize the risk for patients.

1:22

Now, let's examine this particular slide.

1:26

I'd like to demonstrate this one is the main sources of

1:29

radiation exposure in any X-ray room, CT,

1:33

X-rays, or fluoroscopy. The three main sources are primary

1:37

radiation, scatter radiation, and leakage radiation.

1:42

The primary radiation is well collimated.

1:44

When you turn the X-rays on, the primary radiation cannot go

1:48

beyond the size of the image receptor.

1:51

They can go beyond about half an inch outside the receptor, but not

1:55

beyond that. So if you are in the X-ray

1:58

room working with a patient,

2:01

unless you are in the path of the primary beam, you can be

2:05

assured there is no exposure to primary radiation.

2:09

On the other hand, even though the X-ray tube is well collimated, there is

2:13

some leakage, minuscule leakage, and it is defined by the

2:17

FDA, how much, what's the maximum leakage it can give, and

2:21

that is also there.

2:23

But more importantly, the point which we are always concerned are the

2:26

scatter radiation. Scatter radiation comes

2:30

as the primary beam passes through the patient.

2:33

The primary radiation get absorbed

2:37

or scattered, and the scatter is distributed all around the patient.

2:41

It goes in all direction.

2:43

This is one of the reason why

2:45

we working in the fluoroscopy suite has to do all the

2:49

precautions to protect us from scatter radiation.

2:54

Any precautions taken to protect from scatter radiation will

2:57

automatically help to reduce or protect from the leakage

3:01

radiation.

3:03

This is a typical radiation pattern

3:06

in an interventional fluoroscopy system.

3:09

If it is a radiology department, if it is an under the table fluoroscopy

3:13

system, all this under the table will be blocked

3:17

by the table itself.

3:19

But in the interventional system, since it is a freewheeling

3:24

and the CRM can be rotated any direction, any plane,

3:28

and the patient is lying in the patient table, which is a translucent table,

3:32

has a much carbon fiber material, which has a minimal

3:36

X-ray absorption. And this X-rays, the blue one, is the

3:40

primary radiation based on the collimation exposing the patient,

3:44

and the physicians are working here to intervene with the interventional

3:48

procedures.

3:49

This is a typical scatter pattern coming out of the patient in all

3:53

direction.

3:55

Now,

3:56

the primary beam is like this.

3:59

The scatter beam is like this.

4:01

If this is a X-ray table covered completely, this is

4:05

completely protected to the staff working around.

4:08

However, in the interventional, this is not protected because of the free

4:12

table. Therefore, radiation protection principle becomes even more

4:16

important in this situation.

4:19

Just to show you an example of the amount of scatter coming out of the patient,

4:23

this particular graph is a view from the top down to the floor.

4:27

For an average size patient, and you're getting a decent image, that's the

4:31

understanding. The scatter radiation is every black dot.

4:36

The square block is half a meter block, 50 centimeter.

4:40

You can see here.

4:41

So basically, what it's showing is like further away,

4:45

far away from the patient here, less one gets scattered.

4:49

That is also utilized in radiation protection principle to use

4:53

distance to our advantage.

4:56

Now, I look this as more like a butterfly.

4:59

On the body of the butterfly, the patient, and the wings as the

5:03

scatter radiation distribution.

5:05

The wings are thicker at the edge, at the connecting point of the body,

5:09

and becomes thin at the edge. The same thing, analogy can be thought of for

5:13

the scatter radiation here.

5:16

What is the effect of field size? Means the collimation to the

5:20

patient.

5:21

In these three scenario,

5:23

there are dual advantage of collimating to the field.

5:28

As discussed earlier, if you collimate to the field of interest, the image

5:31

quality also improves in fluoroscopy.

5:34

However, in addition, the scatter radiation is also

5:38

minimized, and the patient dose is also

5:41

reduced. So in these instances, for example, this is

5:45

an average size patient. The field size is 30 centimeter by 30

5:49

centimeter, and here is a scatter pattern, quite intense,

5:53

surrounding the patient.

5:55

If the field size is decreased to 50%, means you're only

5:58

collimating more closer to the lumbar spine where you're doing a

6:02

procedure. Automatically, the patient dose is decreased by

6:06

50%,

6:08

and the scatter radiation goes down quite dramatically.

6:12

If the collimation is able to collimate even further,

6:16

and here looks the patient scatter radiation.

6:19

So the take-home message is field size has a direct

6:23

impact on the patient dose and also on the

6:26

radiation to the people working around in the fluoroscopy.

6:31

In this one, demonstrating what is the impact of patient

6:35

dose on the patient size on scatter

6:39

radiation. So there is a three panel shown here.

6:42

What I'm trying to show here is, on an average size patient,

6:46

the entrance skin dose is about 11 milligray per minute,

6:50

let's say.

6:52

And because of that, and again, fluoroscopy has the principle of

6:56

automatic exposure control. Because of that, you can

7:00

see here if the patient size increases, the system

7:04

automatically drives up more radiation.

7:08

So from 11 milligray, it drives up to 33 milligray per minute

7:12

when the patient size is higher. And even for more obese

7:16

patient, the primary radiation is almost eight times

7:20

than the earlier one.

7:22

What does that have an impact on the personal working around, that is

7:26

the scatter radiation? So in an average size patient here,

7:30

when the

7:32

entrance skin dose or the patient is giving 11 milligray

7:36

per minute, the operator collar level is getting about

7:40

0.44 milligray per hour,

7:42

and the

7:44

waist is getting about one milligray per hour.

7:47

And that will jump out to two and four or

7:51

eight depending on the patient size.

7:54

So basically, the scatter radiation increases

7:57

significantly as patient size increases.

8:02

What about the effect of geometric magnification?

8:05

This is very important, and we use it a lot in our teaching

8:09

our new residents and fellows.

8:11

Where to position the patient with respect to X-ray tube.

8:15

First of all, they need to understand where is X-ray tube and where is the image

8:19

receptor. Shown here is the image receptor, which is the

8:23

I.I. Let's say in this scenario,

8:26

the patient is quite far away from the X-ray tube,

8:31

most closer to the image receptor.

8:33

By having this way, the skin dose, let's say we keep it as

8:37

one dose unit,

8:40

and the magnification factor of the anatomy is about 1.25,

8:44

because of the distance.

8:46

Now, if the patient is more closer to the X-ray tube,

8:51

and there's lot more gap here, this will result in the

8:55

entrance skin dose to increase from one unit to

8:58

1.8 dose unit, 80% more dose to the patient.

9:02

And then the anatomy is also exposed, so you have

9:06

lesser area to view on the image.

9:10

This should not be done. In this case, the patient is

9:14

very close to the X-ray tube.

9:17

There is lot more magnification, and the skin dose

9:20

now is higher by about four dose unit.

9:24

So understanding the geometry of the system and where

9:28

you place the patient is critical in minimizing the

9:32

patient dose.

9:34

This technique is recommended in interventional fluoroscopy only,

9:38

not for routine fluoroscopy. Because in interventional fluoroscopy, let's say

9:42

cardiac cath, when you're doing a cardiac stent or EP procedure,

9:47

the system will remain in the same location for a long time because you're

9:50

utilizing the same area where you're trying to thread a needle through the vessels.

9:55

In that case, allowing all the radiation dose to entry to the one point,

10:00

if we slightly change the angulation, that will

10:04

change the location of the skin receiving the peak distribution

10:08

slightly where it is, and we call it as dose

10:11

spreading or dose painting phenomena.

10:15

We are not stopping the total dose to the patient, but the total dose is not

10:19

delivered to the same skin point, but it can be delivered around the

10:22

patient so that it minimizes the radiation risk to the

10:26

patient.