Rad Bio Risk Flashcards
Maximum Permissible Dose (MPD)
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
Occupational limits
5.0 rem/year (5,000 mrem)
50 mSv
Non-occupational limits
0.5 rem/year (500 mrem)
5 mSv
dental personnel avg =
0.2 mSv
sources of radiation exposure to the US population
~ of
radiation
exposure
1/6
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.
Nuclear medicine and CT exams
Medical imaging
> –% of
radiation
exposure ! ! !
50
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 —
age
decades
radiosensitive
children are inherently more radiosensitive (2)
●larger proportion of dividing cells
●less shielding of radiation
sensitive organs
*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%)
5.5 to 6.0
3.0 – 3.5
3
1.5
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%)
4 to 5
3
2.8
1.2
skipped
Age in
years
Female
% Risk of Fatal Radiation
Induced Cancer
10
20
30
40
50
16.8
9.5
8.5
4.0
2.8
skipped
Male
Risk of Fatal Radiation
Induced Cancer
10
20
30
40
50
12.5
7.5
7.0
3.0
2.5
Pediatric tissues at
greatest level of
radiosensitivity due to
rate of cellular and
organ growth
Greater life expectancy
puts children at —
greater risk of being
afflicted with a radiation
induced cancer
2-10
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. )
71
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
1514 uSv
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
355
skipped
— new ortho patients with 3 CBCTs each over a 2 year period
500
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
38
US dentists may cause 967 cases of cancer per year from dental radiography
Use of — and selection criteria could reduce this to 237
rectangular collimation
The trend in orthodontic treatment is to replace lower dose panoramic and
cephalometric radiography with
higher dose cone beam computed tomography
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
1:6,000 (vs 1:1,000,000)
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
low dose radiation exposure from CT scans in young patients
Threshold Non-Linear Curve
(3)
- 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
Radiation Erythema
* 250 Rads –
* 500 Rads –
* 750 Rads –
Threshold radiation Erythema Dose (TED)
Average radiation Erythema Dose
Maximum radiation Erythema Dose
skipped
1959
In 1959, dental radiation dose was
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
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)
2
62
20
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
298
298
Linear Non-Threshold Curve - 1
(2)
- Dose is proportional to the response
- No matter how small the dose, there is some
damage
Linear Nonthreshold Curve -2
(2)
- No threshold
- Minimal damage at first with increased rate
of damage with increased dose
SELECTION CRITERIA
FDA/ADA
* Imaging requires —
* Need a specific …
* An — is required to make
this assessment
justification
question or a diagnostic
task where radiographs will provide unique
information not readily available from
other diagnostic means
initial clinical exam
Patient Shielding During
Dentomaxillofacial Radiology
Recommendation 1 -
Recommendation 2 -
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
