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0:28

We are honored to welcome Dr.

0:30

M Mahesh for a physics board review in radiation protection.

0:34

Dr. Mahesh is a professor of radiology

0:36

and cardiology at Johns Hopkins School

0:38

of Medicine in Baltimore, Maryland.

0:41

Additionally, he's the chair of the Radiation Control

0:43

Committee, president of a A PM Board, member

0:46

of a CR subject matter expert for U-N-I-A-E-A

0:51

and an elected member of NCRP and ICRP.

0:55

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Please remember to use the q

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and a feature to submit your questions.

1:00

With that, we are ready to begin today's board review. Dr.

1:03

Mahesh, please take it from here.

1:07

Wonderful. Uh, welcome back to this physics review,

1:11

and I'm happy to share my knowledge about this

1:13

radiation protection.

1:15

Um, and a few question on radiation biology also, uh,

1:19

this is a topic of interest, not necessarily just

1:22

for the board exam,

1:24

but eventually even for your practice lifelong.

1:27

And this is pretty much very practical, uh,

1:30

information which I want to share.

1:32

So having said that, let's start with the first question.

1:35

What is the unit of effective dose?

1:44

Correct? The answer is C word.

1:46

He is a French physicist

1:48

or German physicist who celebrated his birthday recently,

1:51

who did, who did some fundamental work in this area.

1:55

Um, so let's go to the next question.

1:58

Which cell division stage is most radio

2:02

sensitive to radiation?

2:10

Correct. The answer is correct.

2:12

Metaphase, that's the most a sensitive area when the cells

2:16

is about to divide.

2:17

Um, if the radiation interacts at that time, um,

2:21

there's a chances, um, is uh, effect is even more.

2:25

Next question. What is the maximum annual permissible

2:30

exposure for whole body to a radiation worker in the us?

2:35

These are the choices.

2:42

The answer is, uh, 50 milli word

2:45

and the cancer is correct, 50 milli seabert.

2:48

That's the annually permissible exposure

2:51

for a whole body to radiation worker.

2:53

And, uh, this is recommended by the NCRP,

2:56

which is a National Council

2:58

of Radiation Protection and Measurement.

3:00

They recommend these type of values, uh, recommended limits

3:04

and, but they don't make regulation.

3:06

But usually FDA

3:07

and the NRC are the EPA make the regulation, the us What?

3:12

So next question. What dose metric is useful

3:16

in estimating cancer and hereditary effects from radiation?

3:21

Choices are organ dose, effective dose, peak skin dose,

3:26

and detected dose?

3:33

The answer is effective dose correct Organ dose are also

3:37

important, but here we are talking about, um, estimating,

3:41

um, estimating cancer and risk.

3:44

Uh, when you say estimating cancer, it's the, um,

3:48

the effective dose is the most common, um, uh,

3:51

metrics we use

3:52

because effective dose gives us an way to estimate the risk

3:57

to the whole body from radiation exposure

4:00

to any one part of the body.

4:02

And that's how we incorporated or calculation.

4:04

For example, if you have a head ct, uh, what is,

4:07

if you calculate the effective dose we can see is

4:10

that ranges that from that information we can estimate risk

4:15

to the whole body like cancer causing cancer

4:18

or ary effect effect and so forth.

4:20

So effective dose is the most common

4:22

is the dose metrics used.

4:24

Organ doses are also critical important

4:27

because that are,

4:28

those are included in the effect two dose calculation.

4:31

I will, we will go into details later.

4:33

Peak skin dose on the other hand is the one which is used

4:38

for, um, estimating the skin dose to the patient

4:42

undergoing like interventional cardiology

4:44

or interventional radiology where the peak skin dose

4:48

or the entrance skin dose can give an idea

4:51

for the deterministic effect or the tissue effect,

4:54

but not on the cancer risk.

4:56

Detected dose is nothing to do with the patient.

4:58

It is more of the dose required to create a certain, uh,

5:02

images of certain image quality.

5:06

What is the unit of observed dose

5:14

Is gray.

5:15

That's correct. Um, the observed dose is defined, is defined

5:20

as the amount of energy observed in the unit pass of mass,

5:24

and it defined as the amount of energy is measured in JUULs

5:28

and the amount of ma mass is measured in kilogram.

5:32

And the, the ratio of JUULs

5:34

or divided by kilogram is gives what is called a the gray

5:38

grays again, um, uh, associated

5:41

with the German physicist gray who dial, who develop.

5:44

Some of this fundamental concept I also want

5:47

to say is like in the us we still use the old unit in

5:50

radiology such as the ranking, uh, rad

5:54

and ram gray is the yes si unit

5:58

rad is the old unit

6:00

and you need to know the conversion one gray cost 100 rad.

6:04

That is the conversion.

6:07

Typically most of these diagnostic imaging procedures,

6:11

the observed those range around in milli grade,

6:14

milli grays 1000 of a grade.

6:17

So these are the range of conversions you need

6:19

to understand inspective observe dose.

6:22

Another thing which I want

6:24

to say is like when you say observe dose to a patient,

6:28

actually we don't measure the observed dose.

6:30

We can only measure the, the dose,

6:34

the radiation entering the body at the surface.

6:36

From there we can calculate the observed dose by multiplying

6:41

by a, um, absorption factor called the F factor.

6:45

And these F factors are published in literature

6:47

for variety of tissues.

6:49

So that's how this observed dose is calculated.

6:53

What is the regulation regarding radiation exposure

6:56

for pregnant workers in the us?

7:05

The answer is no more than 0.5 milli ut per

7:08

month is the better choice.

7:09

That is correct. And the reason is like

7:12

when a radiation worker, she's pregnant,

7:16

that's when the employee is obligated to monitor the,

7:20

the dose, the pregnant dose, a radiation worker dose.

7:23

And the way it is monitored is

7:25

during the entire gas station time, the,

7:28

the total dose the person can get is about five milli ct.

7:33

And in any one month it cannot be more than

7:36

0.5 milli seaward.

7:38

The way we monitor in the hospital is we,

7:42

the radiation workers moment,

7:43

she's declared pregnancy the radiation safety officer,

7:47

the office provide two radiation badges, monitor units, one

7:51

to wear outside the apron, uh,

7:53

and one to wear underneath the apron near the abdominal,

7:57

more like a fetal dose measurement.

8:00

And these two are taken into account and any, and,

8:04

and we are also cautioned that workers don't

8:07

exchange the badge to where they're supposed to wear it,

8:10

but either way it should not be more than point milli C five

8:14

milli c per month.

8:17

What is the average background?

8:19

Annual, um, radiation exposure in the United States?

8:29

The answer is three milli C word.

8:32

Um, again, um, the, this is an approximation

8:36

and I said this is an average background annual radiation

8:40

exposure and there are some area in the US which receives

8:45

very high radi background radiation such as, um,

8:48

in general Denver, Colorado

8:50

or where it is up in the mountains,

8:52

the height more higher it is.

8:54

And because of the lot of radium deposits,

8:57

the natural background radiation is can be as I as

9:01

10 milli c word per year.

9:03

But across the US the number we use, uh, citing

9:07

or an average exposure is three milli C word.

9:10

Why is this important for radiologists?

9:13

Because sometime it helps when you're trying

9:16

to communicate the radiation risk to the patient

9:18

or from a particular imaging study, we use this information

9:22

to provide some type of a relative comparison

9:26

to put the dose levels in perspective.

9:28

Because if you simply give some number from HSC CT

9:32

or a head ct, some milli c word it by,

9:35

by in itself doesn't make any sense at that time.

9:38

These type of information is very helpful.

9:43

What is the radiation quality factor

9:45

for x-rays and gamma ray?

9:54

So the answer is all over the place here,

9:56

but majority of you chosen is one that is correct.

9:59

So what is quality factor?

10:02

So what is quality factor is defined as follows.

10:05

Different type of radiation has different quality factor.

10:09

The reason is if the, for the same type of amount

10:13

of exposure and neutron exposure will have 20 times more

10:18

damaging capability compared to x-rays or gamma ray.

10:22

And that is why we account this what is called

10:25

as the radiation quality factor, as

10:28

as an important factor in radiology

10:31

and in radiation oncology.

10:32

Luckily in radiology, since we use x-rays

10:35

and gamma rays, the quality factor is one.

10:38

So the way we do is like we take the absorbed dose

10:42

multiplied by the, uh, the type

10:44

of quality factor will give you the dose

10:47

equivalent to the patient.

10:49

So what I meant to say is like, uh,

10:51

if there is a certain amount of exposure

10:54

is from x-rays versus alpha particle, the damage,

10:58

the biological damage is 20 times greater

11:02

with alpha particle compared to the x-rays

11:05

and that's accounted in the radiation quality factor.

11:09

According to ICRP report 1 0 3, the most

11:14

radio-sensitive organ is

11:23

Interesting.

11:23

Many of you have been reading the book.

11:25

I suppose that's why the correct answer is breast

11:28

because ICRP stands for International Commission

11:33

of Radiation Protection.

11:34

This is the international body which provides based on the

11:39

current, uh, based on the time period research information

11:43

puts out, uh, re um, documents or policies and reports.

11:47

And this ICRP report 1 0 3 is the latest report which goes

11:52

through the, um, tissue, tissue weight factor.

11:55

It's called the tissue weight factor.

11:58

Um, shown here is the breast tissues had a lower weight

12:02

factor earlier in the IC RRP one 60,

12:05

just 60 published back in 19 19 87

12:09

when the new IC RRP report 1 0 3 was published in 2007.

12:14

The, the prevailing research that led to the committee

12:17

to change the weight factor 1.05, 2.12.

12:22

And at the same time historically we all assumed goads are

12:25

the more, most radios to radiation

12:29

actually goad are now degraded, are now con considered not

12:33

that sensitive compared to other tissues such as breast,

12:37

red marrow, lung tissue and so forth.

12:40

So this is an important findings

12:42

and uh, which is going to be there for a few more years.

12:46

And for disclosure, I'm one of the elected member

12:49

of the ICRP committee.

12:51

We are actually now already started looking

12:54

for is there these waiting factor need to be changed or not?

12:58

And we are already putting together this groups

13:00

to do some investigation

13:02

and come up with a report pretty soon.

13:04

But until that the ICR 1 0 3 stands,

13:08

so the breast tissue is the most sensitive than the goads.

13:14

What is LD 50 30 for adult humans.

13:23

Okay, so first of all, this is, uh, you need

13:27

to know what is ld?

13:30

LD stands for lethal dose.

13:32

And then you also need to know what is 50

13:35

and what is 30 nomenclature really means.

13:38

So in the radiation biology

13:39

or in radiation protection,

13:41

this LD 50 30 is really important

13:44

and is it is defined for various tumors and various cells

13:48

and also for adult tumors.

13:50

And this particular concept becomes very important

13:53

with respect to analyzing the any radiation accidents

13:57

or, uh, terrorist, uh, uh, radiation accident

14:00

or cherno and so forth.

14:02

What it basically says,

14:03

like lethal dose 50 means 50% of the population

14:09

will die within 30 days.

14:11

That's what LD 50 30.

14:13

The first number tells what percentage of the population

14:16

will pass, will die,

14:18

and the second number tell you what at what time period.

14:22

So if a population is exposed to three grades,

14:26

that is the whole body is exposed

14:28

to approximately three grave exposure,

14:31

which can only happen in some type

14:33

of a nuclear accident or disaster.

14:36

In that case, we, we can expect almost 50%

14:39

of the population dying in 30 days.

14:43

So whole body radiation that can be lethal in 50%

14:46

of the exposed population within 30 days.

14:49

There is other others also is listed as, uh,

14:52

LD 50 10, 30, 50 to 60 and 160.

14:56

What I want you to remember is like

14:58

what the first number tells the percentage

15:00

of the population passing away.

15:02

And the second number indicates the time period

15:05

For adult humans it's about three grand approximately.

15:09

So without any medical inter in intervention,

15:13

actually the little dose for humans are usually given

15:16

as LD 50 60, at least 51.

15:19

The population will pass away in 60 days without any

15:22

intervention and that amount is three to four gram.

15:29

What dose levels given in gray leads

15:32

to permanent sterility in females?

15:41

This again, the answer is, um, the answer is five gray

15:45

and I I um,

15:47

and this is approximation, I just want to tell even though

15:50

for those people who are told, one, choose a one, um,

15:54

or eight, it can happen to some females,

15:57

but in general account of radiation biology

15:59

and textbooks, we use what is called as the PHI grave

16:03

for per permanent sterility.

16:05

So, um, the, that varying degree

16:08

of sterility can occur due to radiation exposure

16:13

and especially this is, uh, uh, discussed more

16:16

with the patient undergoing radiation therapy,

16:19

but not with in imaging

16:21

or anything only there, the therapeutic dose is so high

16:24

and especially patient, female patient, were about to, um,

16:28

have child or

16:29

before children, they indicate

16:32

that if the dose is more than five grade, that can lead

16:35

to permanent ality, even a lower level of, um, uh,

16:41

exposure up to 10 rad.

16:42

A 0.1 grade can lead to depressed sperm population,

16:46

but usually that comes back.

16:48

So these are some of the effect

16:50

of re on the reproductive organ when large quantity

16:53

of radiation dose is, is inclined, uh,

16:56

is incident on these type of organs.

17:01

What is the most probable radiation effects on unborn

17:06

due to radiation exposure during second or third trimester?

17:17

Answer is increased childhood leukemia, um,

17:20

spontaneous abortion congenital mal fashion.

17:23

So the, our understanding is during the second

17:25

and third trimester, the chances is more

17:28

for a congenital malformation for large quantity,

17:32

every radiation exposure will have certain chances

17:35

for childhood leukemia, but the chances

17:37

of congenital malformation is higher if the exposure occurs

17:41

second to third trimester.

17:42

Let's look at here. This is the current

17:44

understanding we have.

17:46

So let me see that I don't like this one.

17:49

Here is the pipe picture shown here.

17:51

This is a radiation irradiation of a mouse.

17:55

Prenatal development in a mouse can be kind of, uh, similar

17:58

to what the pregnancy of the pregnancy model is.

18:02

And here on this mouse model, um,

18:04

all these mouse model at various stages

18:06

of this conception is given 200 ranking of exposure.

18:10

That's a large radiation exposure when the, if

18:13

during the first trimester, if it happened,

18:15

the chances are more of a prenatal death

18:17

or embryonic, um, death.

18:20

But if it is more of a second trimester

18:22

and third trimester as I mentioned,

18:24

that's when organogenesis time,

18:27

that's when grass congenital malformation is more chances.

18:31

Of course, there is always child like risk

18:33

of childhood cancer that with any type of exposure,

18:37

but more the gross ular malformation is the correct answer.

18:40

The last part is, uh, this, I'm gonna discuss it later.

18:44

Um, any exposure to the fetus more than a hundred milli K

18:48

during the first six weeks

18:49

of conception is generally considered cutoff point

18:54

above which some type of intervention is considered.

18:57

Again, it is only considered but it's not a uh, threshold.

19:02

Um, for example, how many, how much one get a hundred

19:06

milligram or 10 rad of exposure?

19:09

Uh, typically, um, a an abdomen

19:12

and pelvic CT gets about 10 milligram.

19:15

So you're talking about under,

19:16

unless the pregnant patient is scanned 10 times

19:19

during the first six book,

19:21

the pregnancy only then the person's doses gets

19:24

fetus can get to this level.

19:26

So generally, if the clinically indication is strong

19:30

scanning or scanning using CT scan even

19:32

during the pregnancy is considered fairly decent

19:35

or considered fairly safe as long as it's clinically strong.

19:41

What is the maximum permissible exposure

19:44

for whole body to general public?

19:53

That's correct. The answer is this is the general body.

19:56

General public is one.

19:58

What it basically means is like we group people, those

20:01

who are working in a radiation environment are considered

20:04

radiation work such as radiologists, physicians

20:07

and, uh, technologists or medical physicists.

20:10

And we are assigned a radiation badge.

20:12

We are monitored, but everybody else in the area

20:15

are in the hospital or in general public are considered

20:18

general public and they're allowed

20:21

for maximum permissible exposure from these type

20:24

of exposure is not one one milli c you,

20:27

you can ask the question, oh,

20:28

the annual background radiation three receiver.

20:31

This is pertains to

20:32

what the general public can receive if they're

20:35

around the hospital or around the x-ray area.

20:38

And that limit is one milli C

20:40

and this also indicates this cannot used

20:44

as a reference point for how the reconstruction is done,

20:47

how the x-ray rooms are built.

20:49

We call it what is called as the x-ray shielding.

20:52

We use lead line walls for protect the anybody standing

20:56

outside, uh, who should not get more than one milli ct.

20:59

That's the, that's the one of the utility

21:01

of this particular, uh, uh, value.

21:06

What is a single radiation dose, uh, threshold for onset

21:11

of temporary appellation?

21:19

The answer is three gray is correct.

21:22

Um, the, this is a temporary appellation

21:25

and that's an approximately what is acceptable value.

21:28

Here are various threshold dose to skin, um,

21:32

for different type of radiation induced injuries.

21:35

And this on the third column is given the weeks to onset.

21:39

So a temporary appellation

21:41

or a early transient erythema goes around between two

21:44

to three gray of skin dose

21:47

and that usually shows up within one to three weeks.

21:51

Those a lot of the patient don't complain

21:53

because that will go away.

21:55

Only when a patient has received more than six gray

21:57

or seven gray, that's when they experience main erythema,

22:01

the permanent erythema

22:03

or a permanent ablation, which usually unset one

22:06

and a half to three weeks and we can see greater number

22:09

of dose if you go down the list.

22:11

These are different injuries which are ob observed.

22:14

Here is an example, um, shown here.

22:17

This is a, um, uh, various cases explored in the literature

22:22

due to interventional fluoroscopy cases area.

22:25

This is a cardio interventional cardiology procedure

22:28

where the breast was too close causing this type

22:30

of a skin injury on the breast.

22:33

On these two cases are ex very extreme case

22:35

where probably the elbow was very close to the x-ray tube

22:39

for the entire duration

22:40

of the procedure resulting in a complete hollowness

22:44

of the skin leading to the complete bone.

22:46

This is like really serious injury, very rare,

22:49

but we have seen many,

22:50

many cases in this over my period of experience.

22:55

What is the unit of equivalent dose?

23:04

The answer is, uh,

23:07

is correct, is C word.

23:10

Now you can ask the question

23:11

because earlier I asked the question, what is the unit

23:13

of effect to dose and the, the unit was also C word

23:17

and what is the unit of equal in dose?

23:19

That's also C word.

23:21

Then the question is, what is the difference

23:22

between equivalent dose and effective dose?

23:25

Equivalent dose is the way

23:27

we calculate from the observed dose multiplied

23:31

by the radiation quality factor.

23:34

We get equivalent dose.

23:36

So the observed dose is usually graves gives in a gray

23:41

multiplied by the radiation weight factor

23:43

that is the quality factor such as for x-rays

23:46

and gamma A is one

23:48

therefore a gray of observed dose equal to one ra, one C

23:53

of F equivalent dose, the different in equivalent dose

23:56

and effective doses in effective dose.

23:59

We multiply that by a tissue weight factor,

24:02

which we are showed earlier

24:04

by multiplying another constant factor.

24:07

The these, the, the unit remains the same

24:10

as seabert probably.

24:15

We are wondering why all these things,

24:17

one way we can think about is we want medical physicists

24:19

to keep our jobs, so we need to keep confusing.

24:21

No, just kidding, but that's what is derived towards account

24:25

for this dose equivalent and dose equivalent effort to dose.

24:29

So what is the maximum permissible exposure

24:33

for radiation workers for skin, hands and feet?

24:44

The answer is, um, we have variety of answers,

24:47

but the majority answered 500 milli ct

24:50

and that is, that is the correct answer.

24:53

Um, 500 milli ct.

24:55

Now the question comes into page why, um, skin, hands

24:58

and feet can take larger amount compared to the whole body,

25:02

which is 50 milli ct.

25:03

The answer is the organs are tissues associated with skin,

25:07

hands and feet are less radio sensitive, uh, uh, tissues.

25:13

Therefore they're allowed to live a higher threshold

25:16

because even with this one, the da, the the,

25:19

the damage is not that obvious.

25:21

So that's why skin, hands

25:22

and feet can given li uh, limit up to five milli receiver.

25:26

So the next question is

25:28

how does one can get this amount of radiation?

25:31

Let's say for example, if you are an interventional

25:33

cardiologist or if you are an interventional radiologist,

25:36

you are working with the patient around the patient,

25:38

your hands may be in the path of the primary beam.

25:41

That's one exposure.

25:43

The other one is like in the, in the cyclotron facilities

25:46

or in a pet city lab where there is a radio chemist

25:50

who draws out these isotope from the cyclotron, uh,

25:54

separates them and uh,

25:55

separates them into different quantities and so forth.

25:58

Their hand exposure can be as a, can go up high

26:02

and that this allows us for them

26:04

to work without seeing detrimental effect.

26:10

Standing closer to x-ray tube side than image receptor side

26:14

during fluoroscopy provides greater radiation protection.

26:24

So 20% said true majority said false.

26:28

The answer is false

26:30

because for this reason, look at the radiation pattern

26:34

around the interven fluoroscopy system.

26:37

This is a, in the AP direction,

26:40

in the interventional fluoroscopy,

26:42

the table is a free floating table.

26:44

So the table don't protect any radiation protection,

26:47

whereas in a general diagnostic radiology fluoroscopy

26:50

system, the x-ray tube is inside the table.

26:53

So a lot of this is blocked.

26:56

So in general, what happen if you're standing close

26:58

to the x-ray tube side,

27:00

you not only get scatter radiation from the patient,

27:03

you can also get some leakage radiation also to the,

27:05

from the patient from the x-ray tube.

27:08

So that's why this is two to three times more dose.

27:11

Whereas if you're standing closer to the AI side,

27:14

image receptor side, let's say uh, uh, in this days

27:19

what happened is less scatter is coming out

27:22

of the patient here compared to here

27:24

because there's also back scatter.

27:26

And, um, but, and also

27:29

and plus, sorry, plus this, um, this image receptor

27:34

bringing closer to the patient can block lot

27:37

of this scatter coming out also,

27:39

therefore, the scatter radiation is much lesser on the image

27:44

receptor side compared

27:45

to the radiation on the radiation exposure On the x-ray tube

27:48

side, Which CT exam is impacted most

27:54

in terms of affected dose

27:56

by ICRP tissue waiting factor 1 0 3.

28:06

Interesting. So now, uh, 40% of the same got chest CT

28:10

and 40%, 43% got abdominal ct.

28:13

So if you remember back in, uh,

28:15

I CRP 1 0 3 tissue waiting factor,

28:17

which are discuss showed earlier,

28:19

the tissues involved in the chest CT areas,

28:21

the breast which are higher with tissue weight factor,

28:24

whereas the tissues involved in the abdominal C,

28:28

the one which is have gone down,

28:30

therefore the answer is chest CT

28:32

with a new tissue waiting factor.

28:34

The chest CT doses in terms of affected dose is higher.

28:39

This is also one of the reason why

28:42

we medical physicists do not encourage vendors

28:45

to display effective dose value on the monitor.

28:49

We only want them to display observed dose, uh,

28:52

and uh, scale entrance dose, but not the effective dose

28:55

because the effective dose need

28:58

to be computed based on the prevailing tissue waiting

29:01

factor, which a medical physicist

29:03

or the radiologist will know at that particular time period.

29:07

Therefore, in this particular choice head CT

29:09

and extremity ct, they're not impacted

29:12

by the tissue weight factor.

29:13

The one which is impacted

29:14

by the tissue weight factor is this, uh, uh, chest CT

29:18

because the breast dose is now going to be almost, um, uh,

29:22

30 times percent more,

29:24

therefore this is impacted According

29:28

to n CRP one 60.

29:30

What is the maximum permissible dose

29:32

to x-ray technologist on an annual basis?

29:42

And the answer is 50.

29:43

That's, uh, because technologies

29:44

that considered the radiation worker,

29:46

therefore the maximum permissible dose is 50 milli.

29:50

So I just summarize this whole

29:52

thing in this particular table.

29:54

This is again given by the NCRP report, NCRP stand for

29:59

National Council of Radiation Protection Measurement.

30:02

Um, this full disclosure, I'm one

30:03

of the elected council member

30:04

of this than a hundred council member in the country.

30:07

This is a US uh, US government advisory body, um,

30:12

charted by the Congress.

30:14

So this NCRP committees will put out these type of reports,

30:17

but without any, um, recommendation of what to be done.

30:21

But usually these type

30:23

of recommendation are the policies comes out, are picked up

30:26

by the FDA or the EPA or the NRC

30:29

and they make into regulation one such report one 16

30:33

provided these limits and immediately this has become their

30:35

regulation in the US right now, various states

30:39

and, uh, NRC regulates this on the hospital.

30:42

So radiation workers for a whole body

30:45

on an annual dose limit is 50 milli.

30:48

I've also given the older unit, uh, older unit that, uh,

30:53

in, in terms of the ramp here.

30:56

So ICE can go up to 15 milli REM

30:59

or 150 millivolt skin hands and feet is 500.

31:04

What this is called a community dose.

31:06

Any radiation worker should not get more than

31:10

10 times their age.

31:11

In terms of millivolt, let's say you are 35,

31:14

your cumulative dose reading on all the badge

31:17

reading every year.

31:19

If you add up, you should not be more than

31:21

10 times your age.

31:22

Let's say you're 35,

31:24

that should not be more than three 50 milli a

31:27

and for a general public,

31:28

the whole body is one milli c word.

31:31

As I mentioned earlier. This is influences the way we do

31:35

construct the x-ray room, CTR, uh, uh, fluoroscopy suite,

31:39

eyes, skin and hands is given 50.

31:41

Milli receiver for a general public, for a radiation worker

31:45

for the entire gas station is five milli receiver, majority

31:48

of you answered correctly.

31:49

And in many one month it's one 10th of this 1.5 milli c.

31:54

So this table is important for you guys to remember, uh,

31:58

if you and keep it, keep a, keep it

32:00

as a cheat sheet for yourself.

32:01

When you're looking at various, various groups

32:04

and their annual dose limits allowed in the US

32:10

What dose metrics is useful in estimating tissue

32:15

reactions or deterministic effects from radiation?

32:24

So the answer is major 41% said a peak skin dose

32:29

and the answer is, um, peak skin dose.

32:32

So there are two things. The biological effect

32:34

of radiation can be grouped into two groups.

32:37

One is called the stochastic effect,

32:39

which is a long-term effect

32:41

and the best example is radiation induced cancer to, uh,

32:45

to calculate that when we use effective dose term,

32:48

whereas the deterministic effect now we call

32:51

that we change the name from tissue deterministic effect

32:54

to tissue effects

32:56

and that tissue effects are actually calculated

32:59

by the skin dose.

33:00

Peak skin dose are the entrance skin dose in this choice,

33:04

the peak skin dose was the more appropriate one.

33:09

Standing behind a person wearing lead apron

33:13

and facing the x-ray source provide radiation protection.

33:23

The majority said true.

33:24

And actually the answer is true

33:26

because that's why you might be wondering why your physician

33:29

is standing behind you when you are doing a um, uh,

33:32

fluoroscopy procedure

33:33

because you're gonna provide additional protection,

33:35

let's say, and the protection is provided by the apron.

33:39

Apron comes in all one piece or two pieces.

33:42

Recommended level is between 0.25

33:44

to 0.5 millimeter lead thickness.

33:47

And then here is what I meant to say.

33:50

When somebody is standing, we are facing the x-ray tube.

33:54

If you stand behind it,

33:55

that particular person would provide good production.

33:58

This is shown by what is called as a lead barriers,

34:01

which most of the fluoroscopy rooms, at least at Hopkins,

34:05

we have in all the rooms where,

34:07

and a person who's not doing the procedure can simply stand

34:11

behind it because this created a shadow region.

34:13

The same thing applies when you are standing behind a person

34:17

who is wearing a lead apron

34:19

and you stand behind, it means the person will provide

34:21

additional color protection, we don't advise,

34:24

but if you're standing behind it, you still need

34:26

to wear a lead apron and so forth.

34:28

So this is, and this is more recommended

34:31

to have in every room

34:32

because it's gonna create a good area for shadow region

34:36

where, for example,

34:37

a medical student watching the procedure can stand here

34:40

or an anesthesiologist can stand here, work

34:42

behind the procedure and so forth.

34:45

Which statement regarding radiation risk to fetus

34:49

during pregnancy is true.

34:56

Okay, so which is true fetal exposure from head C is minimal

35:01

and is due to majority have selected the correct answer.

35:05

That that is true because I just wanted

35:07

to bring this question because

35:08

or we know microcephaly is, um, reducing the head size

35:14

has shown in some of the survivor, um, uh,

35:17

Japanese Hiroshima Nagasaki survivor, uh,

35:20

who were pregnant at that time, some kids were born

35:23

with the microcephaly

35:24

and it's estimated to be received more than 300 grand.

35:27

Um, therapeutic abortion is disgusted if it is more than a

35:30

hundred milligram, that's also true

35:32

and radiation worker can receive up to 50 minutes per month.

35:36

That's not true. Whereas this one, um,

35:39

fetal exposure from head CT is minimal

35:41

because if there is any, anything happen to the fetus,

35:45

it's only because in this case it's only internal scatter

35:48

and that internal scatter is far away from the head CT area.

35:51

Therefore, the fetal exposure from head CT is minimal.

35:55

And again, this is, these two are not right

35:58

because we are, we talk about this thing,

36:00

but we don't have any evidence of this very directly

36:03

for 300 milli milligram

36:05

or a hundred milligram scatter radiation is larger

36:10

than other type of radiation present

36:13

in a typical fluoroscopy suite.

36:21

Okay? The answer

36:22

with this question is scatter radiation is larger

36:24

than other type of radiation.

36:25

Present is in a fluoroscopy suite.

36:29

Is uh, is uh, true?

36:31

I'll explain it more, but there is some um,

36:33

some alignment of this question lot.

36:35

There is one more question.

36:36

I'm gonna drop this question back

36:38

and let me come back to this question directly.

36:41

The source of exposure in any x-ray room are the following

36:45

primary radiations cat radiation, leakage radiation for,

36:49

for anybody inside the x-ray room other than the patient,

36:53

the, the greatest source

36:54

of exposure is the scatter radiation.

36:57

That's what I meant in the question 23

36:59

and the leakage radiation, there is some amount,

37:02

but that is smaller compared to the scatter radiation.

37:04

So among the three source of radiation, the radiation

37:08

to the person other than the patient in the room is from

37:11

the scatter radiation.

37:13

And that's, I meant to say that

37:15

which is the earliest clinically deductible effect

37:19

of radiation on the skin.

37:27

And the the correct answer is, um, erythema. That's correct.

37:31

And um, uh, the, that is the earliest,

37:34

that is the skin reding effect.

37:36

Even temporary erythema are permanent arrium.

37:38

That's what it's the first clinically indicated effort.

37:41

You see that which of the following is considered

37:44

to offer minimal radiation protection to the fluoroscopist

37:55

And the answer is radiation, uh, uh, surgical blouse.

38:00

And the answer is that's correct

38:02

because we, we had to use protective lead, uh, aprons

38:06

to protect the maximum protection for uh, radiologist.

38:09

We also recommend using thyroid shield,

38:11

we also using C mounted lac,

38:14

but this one few companies try to sell these,

38:16

these are very thin latex blouse which has a lead material

38:21

kind of, but if you happen to use this,

38:24

this actually produce more radiation to the fingers

38:26

and there are excellent pay publication showing that.

38:29

Here's an example of a person wearing that thin blouse.

38:32

You can see here when they are in the path

38:34

of the primary beam, you can see the bony structure

38:37

of the fluoroscopist actually

38:39

because the multiple scatter,

38:41

the finger gets even more than without the glos

38:45

and we call them as emper glos.

38:50

Which of the following imaging procedure

38:53

for a pregnant worker

38:55

will deliver the highest radiation dose

38:58

to six week old fetus?

39:01

What I meant is like for a pregnant patient,

39:09

correct?

39:10

The majority have chosen KUB radius.

39:12

That is correct because KUB involves directly exposure on

39:16

the, on the abdominal area, whereas chest ct,

39:20

the pregnant patient is exposed to chest ct,

39:22

the fetus only gets inal, scatter is much less.

39:26

Abdominal ultrasound does not have any radiation.

39:29

Head CT gets radiation,

39:30

but the inal scatter is low low compared

39:33

to the choice the KUB, the kidney

39:35

and bladder, which is a direct exposure of the fetus.

39:38

So the those so does the radiation exposure is higher

39:43

with KUB radiography series than in any other procedures.

39:50

According to NC RRP 180 4, which CT procedures are done,

39:55

uh, uh, are done mostly in pediatric population

40:00

in the US

40:08

And the answer is head ct.

40:10

You are correct and the choice is correct.

40:12

And again, this NC RRP 180 4 was published in 2019,

40:17

which calculated the radiation exposure

40:20

to US population from medical procedures.

40:23

And when we computed this particular report, we, we saw

40:26

that the, the number of CT procedures done in the us 10%

40:30

of the cts are done in pediatric

40:32

and among the pediatric population, these 10% of the cts,

40:36

majority of them, almost like 80 to 90% were head CT

40:40

because children are brought to the emergency room in the

40:43

fall, the playground

40:44

or some high fever, the common C done is the head C,

40:51

Which imaging modality results in the highest collective

40:54

medical exposure to US population

41:03

ct?

41:03

That's correct. And here is the things,

41:08

this is a really number of procedures, um,

41:11

done in the US versus the average individual effective dose

41:15

for US population in 2006.

41:18

If you look in here, we did about, uh,

41:20

four 91 million procedure in the us So among that majority

41:25

of the procedure were radiography and fluoroscopy

41:28

and uh, CT was accounted to 74 million at that time.

41:31

But when we compute the collective effective dose,

41:35

CT accounted for the majority of the radiation exposure,

41:38

collective effective dose to the population

41:40

ies next one is the nuclear medicine.

41:43

Now later one is the radiography and fluoroscopy

41:46

and followed on the other, other,

41:48

Uh, What is the dose response relationship

41:52

for solid tumors used by BR seven

41:56

and unskilled committees?

42:04

Majority has said linear with no threshold.

42:06

That is, that is correct. That is called the L and T model.

42:10

What is BR seven and unskilled?

42:11

Unskilled is interation committee,

42:13

which puts out periodic reports on the radiation exposure

42:17

to the world population.

42:19

BR seven is the biological effect of ionizing radiation.

42:23

Uh, reports based on the people exposed to radiation

42:27

and the largest group is the survivor

42:29

of the Hiroshima Nagasaki.

42:30

Both of them used what is called as linear

42:33

with no threshold, which means no matter

42:36

how small the radiation, assuming there is a,

42:39

there is a, a radiation effect.

42:42

And this particular model was actually developed uh,

42:45

to give, to discuss

42:47

or provide way for the radiation protection of the workers,

42:52

which means um, the employer need to do all they can

42:56

to minimize the radiation exposure to their workers.

43:00

Unfortunately we also use it for discussing with the patient

43:04

and there's a lot of confusion,

43:05

but the model accepted is linear

43:07

with no threshold even though we don't have much data at the

43:11

lower level radiation doses.

43:15

What is the biggest contributor

43:17

to the annual background radiation exposure

43:19

to US population.

43:27

Okay, sorry, I clicked earlier, but the answer is radon

43:30

and actually radon is the one of the largest export.

43:34

Here is the, um, picture of it.

43:36

So this is the previous report which we published back in

43:40

2006 and you can see a majority of the background radiation.

43:44

50% of the radiation we get is from background.

43:47

If you look in among the background radiation, majority

43:50

of this come from radon art in the, in the uh, cus the next,

43:55

next largest next one is the um, um, a space, uh,

43:59

radiation background or cosmic radiation,

44:02

but majority is the rad radon.

44:06

So let me stop here and I want to have a few more slides,

44:08

but let me come back to the question ask here

44:11

and then I can come back a few more questions here.

44:14

So the questions, there are a couple of questions.

44:16

One was, um,

44:18

does the fluoro machine give the effective dose?

44:20

No, the fluoroscopy machine only provides um,

44:24

community dose, which is like a entrance skin dose

44:27

and also what is called as dose area product.

44:30

It's also called a CMA air product or dose area product

44:34

because community dose is very helpful in assessing the skin

44:38

dose, whereas the dose area product is used in

44:43

assessing the effective dose

44:45

for calculating the risk to the whole body.

44:47

If three gray kills, then why does phi gray for solidity?

44:52

The reason is like three gray.

44:53

When I say three gray that for the whole body exposure.

44:57

When I say phi gray, that's phi gray for,

45:01

for the gonadal region

45:02

or the ovary only, not for the whole body.

45:05

So your question is reasonable.

45:07

So three grade kills means five gray should automatically

45:10

kill, but you have to worry about sterility.

45:12

But here five gray is not to the whole body.

45:15

Just just to the uh, organ of interest.

45:18

The other question, what is the dose when a

45:21

therapeutic abortion discussed?

45:23

Generally we don't, we are not come across any situation.

45:27

We are discussed, but generally when it is more than a

45:30

hundred milli PC word or 110 REM

45:33

or a hundred milli C word, that's the effective dose.

45:36

That's when we discussed about these things

45:39

for consideration, not even as a rule of thumb

45:42

because we don't have good evidence of data,

45:45

something will happen at a hundred milli seaward.

45:48

How does one get a hundred milli seaward, as I said,

45:50

in the abdominal pelvic CT is about 10 milli seaward.

45:54

And unless they get about 10 CT of the abdomen pelvic all

45:58

during the first six weeks of pregnancy,

46:00

that's when one can get that amount of load.

46:03

And over the past, there are so many years of my experience,

46:06

I have not seen anybody get more than one CT of the abdomen

46:09

and pelvic area during pregnancy.

46:11

The next question is, is it recommended to shield

46:14

pregnant patient when not imaging in the pelvic area?

46:17

No, actually there is no need to actually, this is one

46:20

of the things which we are tackling for a long time

46:24

and in the past we used to assume that putting an apron, uh,

46:28

in the, in the pregnant patient when they do a chest CT

46:31

or a head CT will uh, protect it.

46:33

That is no longer true and it's not true

46:36

because we cannot protect internal scatter

46:39

and the radiation, scatter radiation is not so strong

46:41

to reflect off the walls and hit the pregnant.

46:44

On the other hand, it can give a false

46:46

comfort to the pregnant.

46:47

In fact, if you notice that dentist, dentist, if you go

46:51

to dental x-rays dentist

46:53

and when they take an x-ray, they is

46:54

to put a shield on your chest

46:56

and even they have now recommended against it.

46:59

There is no use of putting any shield during the, um, uh,

47:03

imaging, uh, uh, during, uh, dental or any of the x-rays.

47:07

They're not any helpful.

47:09

So I have few more slides I wanna just

47:12

show these are fundamental.

47:13

Uh, one is the how does the inverse square

47:16

applicable in radiology.

47:18

And the way it works is like inverse law work

47:21

to our advantage in radiation protection

47:23

because further away you stand from the source,

47:27

the the radiation reaching will decrease

47:29

by one square one over R square.

47:32

For example, here, this is an average sized patient and,

47:37

and every black.is a scatter radiation.

47:40

And you can see, and this is a 50 meter block,

47:42

50 centimeter block.

47:44

So if, if you stand one meter away,

47:46

look at the scatter you're getting compared

47:48

to standing one very close to.

47:50

So this is very advantage to ourself as one.

47:53

Our R score, again, this come up from the ICRP report,

47:57

1 33 telling

47:58

that further away you stand from the x-ray source,

48:01

less scatter radiation you're gonna get.

48:04

And the way I I picture myself in the scatter radiation is

48:08

imagine in the x-ray room, the patient as the body

48:11

of the butterfly and the scatter radiation coming outta the

48:15

patient is the, is the wings of a butterfly.

48:18

The wing of a butterfly is thicker, closer to the body

48:21

and thinner at the edge.

48:22

And the same analogy goes

48:24

for the scatter radiation is very high, closer

48:26

to the patient and decreases quite dramatically

48:30

as you go down away from the patient.

48:33

So one other concept which I want

48:35

to discuss is the patient thickness has the patient

48:37

thickness increases in fluoroscopy,

48:40

so does the scatter radiation reaching the fluoroscopist

48:44

I I wanna draw here is like this,

48:46

this is 11 milligram per minute,

48:48

that is the intense skin dose

48:50

and the dap reading is multiplied by the area.

48:53

Look at here, this is a two milligram per hour.

48:56

This is cent milli minute and this is milligram hour.

49:00

And you can see here for one hour, if they do the procedure

49:03

of this patient, they may get two milligram here.

49:06

By the time it treats the badges further away from here,

49:09

they get about 0.25 milligram per hour.

49:11

That's why wearing a lead apron is pretty protective,

49:14

which covers three fourths of four body.

49:17

If the patient size is large,

49:19

the fluoroscopic system automatically

49:22

dried the radiation higher.

49:24

Therefore here the patient is getting eight times more

49:27

dose than this one.

49:29

So does the scatter radiation increases.

49:31

Now instead of getting 0.25 milli hour per milligram,

49:34

per uh, per the entire hour,

49:36

it'll get about 0.5 milligram per hour.

49:39

So that's the rule of thumb.

49:41

I wish you best and if you have any question,

49:44

please chat, put it on the chat.

49:46

Otherwise I wish all the best

49:48

and uh, good luck for the exam.

49:51

Excellent, thank you so much again, Dr.

49:52

Mahesh, and thank you. Thank you.

49:54

And thank you to everyone for participating

49:56

and joining us for these rapid case reviews.

49:59

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50:01

and previous case reviews by creating a free account.

50:04

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50:07

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