0:00

Again, recapturing the bigger picture here, the biological effect of radiation,

0:05

stochastic effect, called the delayed effect, non-stochastic effect, also called as

0:10

deterministic or tissue effects. This is a broad category.

0:15

The non-stochastic effect occurs within days to weeks, whereas stochastic effects

0:20

are observed within three to 20 years after exposure.

0:24

And in case of mutations, it usually observed in future generation.

0:28

Here's an example of a deterministic effect, which is very rare but possible in CT.

0:34

These figures were directly from the New York Times article in 2011, where in a

0:39

hospital, they started doing CT perfusion for the first time, and we thought

0:45

something happened. More than 200 patients came back with hair loss.

0:50

Upon further investigation, they found that these hair losses were caused because

0:54

the radiation level set in these protocols, somebody had changed it.

0:59

Changed it in a way understanding they were trying to lower the radiation dose.

1:04

In fact, they increased the radiation dose by eight times, exceeded beyond the

1:08

threshold causing for this deterministic effect, and resulted in this temporary

1:13

hair loss in some of the patients.

1:16

So the radiation induced skin injuries is one classic example which we are

1:22

focused in radiology or cardiology.

1:25

Any place we do long interventional fluoroscopy procedure.

1:30

When you do a long interventional fluoroscopy procedure, there is a high chances,

1:36

or at least there is a chances, that these type of injury can occur.

1:41

Even though these type of injuries are becoming less and less prevalent because of

1:45

the understanding how we do this procedure or the radiation dose per procedures is

1:51

decreasing and so forth, but here's an example.

1:55

On the left-hand side is a table giving the radiation injuries or skin

2:00

injuries and that can result, and what is the threshold dose to cause this injury.

2:07

These radiation induced skin injuries are a classic example of deterministic

2:12

effect, also called as tissue effect, and which means these effects do

2:17

not occur if the radiation level is below this threshold.

2:23

Once the threshold is crossed, these effects becomes almost linear.

2:27

For example, here, the early transient erythema as the threshold dose to skin is

2:33

approximately two gray and temporary appallition is approximately three gray.

2:39

And both of them, the weeks to onset is less than one week or up to three weeks.

2:46

The main erythema is if the dose to the same skin point got more than six gray, and

2:52

that usually onsets after one and a half weeks.

2:55

If you go down the list, like for example here, what you're seeing here is either

3:00

permanent depilation or invasive fibrosis.

3:05

All the worst thing is called the dermal necrosis or secondary ulceration, and this

3:11

particular one image in the center is an example of a secondary ulceration,

3:17

where the radiation dose may be as high as 20 gray and usually shows up after six

3:22

weeks. So on the far end of the image is the image of a person with a

3:28

different shape of the radiation injury, and that is maybe due to biplane

3:33

fluoroscopy procedure, and the injuries are the shape of the collimator, and these

3:38

can go anywhere from permanent depilation, main erythema to dermal

3:44

atrophy and so forth. What about reproductive organs?

3:48

Radiation exposure to the reproductive organs can have an effect.

3:53

They were highly radio sensitive, but it's now decreased to some extent.

3:57

The varying degree of sterility and probability of induced genetic

4:03

effects can occur with radiation exposure.

4:06

Even doses less than 0.1 gray, that is 10 rad, can depress sperm population in

4:12

males and can cause menstrual irregularities in females.

4:17

Shown in this table is the effect in male and female, and the single threshold dose

4:22

which is understood to cause this effect, as given both in terms of rad

4:28

and gray. The temporary epilation can cause if the radiation dose is more than

4:34

two gray, and the permanent sterility can cause if the dose is more than five to

4:39

six gray. And this is important information to be understood when the patient

4:45

undergoes radiation therapy treatment, so that these things can be avoided.

4:51

What about the radiation effect on the unborn?

4:53

The radiation effect on the unborn, the pregnancy, depends on the time of the

4:57

pregnancy. The most sensitive part of the pregnancy is two to 15 weeks, the first

5:02

trimester. As you can shown here on the right-hand side is a picture of the effects

5:08

on the fetuses at various stages of the pregnancy.

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It is shown here, this is the study done on the mice model, mouse model.

5:18

Fortunately, that mimics the human pregnancy model.

5:21

Therefore, trying to understand the radiation biology on the fetus or on the

5:25

pregnant women, we can examine this particular diagram.

5:28

If the radiation exposure occurred during the first trimester, the chances of

5:33

prenatal death is high.

5:35

If the pregnancy has matured and it is in the second or third trimester, the

5:40

prenatal death chances are decreased, but more of these organogenesis chances are

5:46

there. So most sensitive part of the pregnancy is two to 15 weeks

5:52

post-conception. The high chances during the first trimester is the prenatal or

5:56

pre-embryonic death,

5:59

and the fetus exposed to radiation can results in decreasing head size and mental

6:04

retardation, gross congenital malformation, increased risk of childhood cancer.