Rad Bio Risk

Question 1

Maximum Permissible Dose (MPD)

Answer 1

That amount of radiation which in the light
of present knowledge will not produce any
serious, harmful, or deleterious effects on
the individual receiving it

Question 2

Occupational limits

Answer 2

5.0 rem/year (5,000 mrem)
50 mSv

Question 3

Non-occupational limits

Answer 3

0.5 rem/year (500 mrem)
5 mSv

Question 4

dental personnel avg =

Answer 4

0.2 mSv

Question 5

sources of radiation exposure to the US population
~ of
radiation
exposure

Answer 5

1/6

Question 6

In May 2007, the American College of
Radiologists published a white paper
cautioning the medical profession that
Americans are being exposed to record
amounts of ionizing radiation.
* (2) have
risen sharply in this time period.

Answer 6

Nuclear medicine and CT exams

Question 7

Medical imaging
> –% of
radiation
exposure ! ! !

Answer 7

50

Question 8

Estimated Dependence of Lifetime Radiation-Induced Risk of Cancer
on Age at Exposure for Two of the Most Common Radiogenic Cancers.

Cancer risks decrease with increasing —
latency periods for solid tumors are
typically —
children have more years of life during
which a potential cancer can be expressed
children are inherently more —

Answer 8

age
decades
radiosensitive

Question 9

children are inherently more radiosensitive (2)

Answer 9

●larger proportion of dividing cells
●less shielding of radiation
sensitive organs

Question 10

*Females < 10 yo, ~ times more likely to develop
fatal cancer than 50 yo!! (i.e., 15.5% - 2.8%)
*20 yo females are ~ times more likely to develop
fatal cancer than 50 yo!! (i.e., 9.5% - 2.8%)
*30 yo females are ~3 times as likely more develop fatal
cancer than 50 yo!! (i.e., 8.5% - 2.5%)
*40 yo females are ~ times as likely more develop fatal
cancer than 50 yo!! (i.e., 2.8% - 2.5%)

Answer 10

5.5 to 6.0
3.0 – 3.5
3
1.5

Question 11

Males < 10 yo, ~ X more likely to develop fatal cancer
than 50 yo!! (i.e., 12.5% - 2.5%)
*20 yo males are ~ times as likely to develop fatal cancer
than 50 yo!! (i.e., 7.5% - 2.5%)
*30 yo males are ~times as likely to develop fatal cancer
than 50 yo!! (i.e., 7.0% - 2.5%)
*40 yo males are ~ times as likely to develop fatal cancer
than 50 yo!! (i.e., 3.0% - 2.5%)

Answer 11

4 to 5
3
2.8
1.2

Question 12

skipped
Age in
years
Female
% Risk of Fatal Radiation
Induced Cancer
10
20
30
40
50

Answer 12

16.8
9.5
8.5
4.0
2.8

Question 13

skipped
Male
Risk of Fatal Radiation
Induced Cancer
10
20
30
40
50

Answer 13

12.5
7.5
7.0
3.0
2.5

Question 14

Pediatric tissues at
greatest level of
radiosensitivity due to

Answer 14

rate of cellular and
organ growth

Question 15

Greater life expectancy
puts children at —
greater risk of being
afflicted with a radiation
induced cancer

Answer 15

2-10

Question 16

Female orthodontic patients in the age group 11-15 who have more than 1 CBCT in
2 years have a risk of – deaths per million CBCT exposures (median dose of 300
uSv. )

Answer 16

71

Question 17

CBCT Risks
* Female orthodontic patients in the age group 11-15 who have more than 1 CBCT in
2 years have a risk of 71 deaths per million CBCT exposures (median dose of 300
uSv. )
* maximum doses of machines were

Answer 17

1514 uSv

Question 18

In this small group the risk increases to – deaths per million CBCT exposures
– ~2.8 deaths per 10,000 CBCT exposures
– ~1.0 death per 1,000 CBCT exposures

Answer 18

355

Question 19

skipped
— new ortho patients with 3 CBCTs each over a 2 year period

Answer 19

500

Question 20

skipped
with –% females patients aged 11-15 years, then 190 girls every 2 years. In about
10 years the risk of causing one death is high

Answer 20

38

Question 21

US dentists may cause 967 cases of cancer per year from dental radiography
Use of — and selection criteria could reduce this to 237

Answer 21

rectangular collimation

Question 22

The trend in orthodontic treatment is to replace lower dose panoramic and
cephalometric radiography with

Answer 22

higher dose cone beam computed tomography

Question 23

exposing a girl of 10 to 14 years to 3 CBCTs over a 2-year period, the risk of this
child developing cancer is about

Answer 23

1:6,000 (vs 1:1,000,000)

Question 24

although there was evidence of some bias in our original risk estimates, re-analysis of the cohort with additional clinical data still showed an increased cancer risk after

Answer 24

low dose radiation exposure from CT scans in young patients

Question 25

Threshold Non-Linear Curve
(3)

Answer 25

• Small exposures to a substance
  do not produce measurable
  changes
• A threshold must be reached
  before changes are observed
• Most biologic effects are non-
  linear

Question 26

Radiation Erythema
* 250 Rads –
* 500 Rads –
* 750 Rads –

Answer 26

Threshold radiation Erythema Dose (TED)
Average radiation Erythema Dose
Maximum radiation Erythema Dose

Question 27

skipped
1959
In 1959, dental radiation dose was

Answer 27

1 Rad/ second with an 8”
focal distance 10 mA, 65 kV (Ennis and Berry)
28
Maximum allowable x-ray exposure limits were 50% of TED;
i.e., 125 Rads

Question 28

skipped
1959In 1959, dental radiation dose was 1 Rad/ second with an 8”
focal distance 10 mA, 65 kV (Ennis and Berry)
29
One periapical exposure averaged – seconds;
i.e., 120 impulses or 2.00 s; this equates to 20mAs;
1,250/20 = – exposures delivers the TED
1/3 of the TED is delivered with ~– intraoral dental
exposures (one FMS)

Answer 28

2
62
20

Question 29

skipped
2020
It takes 417 mAs/1.4 mAs = ~— exposures
1/3 of the TED is delivered with ~— intraoral
dental exposures
In 2020, 8” focal distances at 7mAs and 0.2 s
(7mA * 02s = 1.4 mAs)
1.4 mAs/ exposure

Answer 29

298
298

Question 30

Linear Non-Threshold Curve - 1
(2)

Answer 30

• Dose is proportional to the response
• No matter how small the dose, there is some
  damage

Question 31

Linear Nonthreshold Curve -2
(2)

Answer 31

• No threshold
• Minimal damage at first with increased rate
  of damage with increased dose

Question 32

SELECTION CRITERIA
FDA/ADA
* Imaging requires —
* Need a specific …
* An — is required to make
this assessment

Answer 32

justification
question or a diagnostic
task where radiographs will provide unique
information not readily available from
other diagnostic means
initial clinical exam

Question 33

Patient Shielding During
Dentomaxillofacial Radiology
Recommendation 1 -
Recommendation 2 -

Answer 33

Recommendation 1
* discontinuing shielding of
the gonads, pelvic
structures, and fetuses
during all
dentomaxillofacial
radiographic imaging
procedures

Recommendation 2
* thyroid shielding not be
used during intraoral,
panoramic,
cephalometric, and CBCT
imaging as the risks of
thyroid cancer are
negligible from
contemporary
maxillofacial imaging
radiation doses
48