managing rad risk

Question 1

Estimated Number of CT Scans Performed Annually in the US.
The most recent estimate of?

Answer 1

62 million CT scans in 2006.

Question 2

occupational MPD

Answer 2

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

Question 3

non-occupational MPD

Answer 3

0.5 rem/year (500 mrem)
5 mSv

Question 4

how much of total radiation to population does ionizing imaging account for

Answer 4

1/6

Question 5

have nuclear medicine and CT use increased?

Answer 5

yes, more radiation exposure to public to more than 50% of total exposure

Question 6

Estimated Organ Doses from Typical
Single Head CT Scan graph

Answer 6

decreased risk with increased age

Question 7

Estimated Organ Doses from Typical
Single Abdominal CT Scan graph

Answer 7

decreased risk with increased age

Question 8

what is the typical age for the beginning of a drop in risk associated with ionizing radiation

Answer 8

around 25

Question 9

age association with risk of malignancy
* Cancer risks decrease with?
* latency periods for solid tumors?
* radiosensitivity? why?

Answer 9

• Cancer risks decrease with increasing age
• latency periods for solid tumors are typically decades
• children have more years of life during which a potential cancer can be expressed
• children are inherently more radiosensitive
  ●larger proportion of dividing cells
  ●less shielding of radiation sensitive organs

Question 10

Effects of Age and Female Gender on Cancer Risk:
*Females < 10 yo,
*20 yo females
*30 yo females
*40 yo females

Answer 10

Question 11

Effects of Age and Male Gender on Cancer Risk:
Males < 10
*20 yo males
*30 yo males
*40 yo males

Answer 11

Question 12

ages: 10,20,30,40,50

Answer 12

Question 13

Pediatric Patients at risk
* Pediatric tissues at?
* Greater life expectancy?

Answer 13

• Pediatric tissues at greatest level of radiosensitivity due to rate of cellular and organ growth
• Greater life expectancy puts children at 2-10
  greater risk of being afflicted with a radiation
  induced cancer

Question 14

• Female orthodontic patients in the age group 11-15 who have more than 1 CBCT in 2 years have a risk of?

Answer 14

risk of 71 deaths per million CBCT exposures (median dose of 300 uSv.

Question 15

• maximum doses of CBCT machines?
• In this small group the risk increases to?

Answer 15

• maximum doses of machines were 1514 uSv.
• In this small group the risk increases to 355 deaths per million CBCT exposures
  – ~2.8 deaths per 10,000 CBCT exposures
  – ~1.0 death per 1,000 CBCT exposures

Question 16

US dentists may cause ? cases of cancer per year from radiation
Use of rectangular collimation and selection criteria could reduce this to?

Answer 16

• US dentists may cause 967 cases of cancer per year from
• Use of rectangular collimation and selection criteria could reduce this to 237

Question 17

dangerous trend in ortho

Answer 17

• 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)

Question 18

Threshold Non-Linear Curve

Answer 18

• 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 (erythema)

Question 19

Rad eryhtmea doses

Answer 19

• 250 Rads – Threshold radiation Erythema Dose (TED)
• 500 Rads – Average radiation Erythema Dose
• 750 Rads – Maximum radiation Erythema Dose

Question 20

1959 exposures

Answer 20

• dental radiation dose was 1 Rad/ second with an 8” focal distance 10 mA, 65 kV
• Maximum allowable x-ray exposure limits were 50% of TED; i.e., 125 Rads
• One periapical exposure averaged 2 seconds;
  i.e., 120 impulses or 2.00 s; this equates to 20mAs;
• 1,250/20 = 62 exposures delivers the TED
• 1/3 of the TED is delivered with ~20 intraoral dental exposures (one FMS)

Question 21

2020 exposures

Answer 21

• In 2020, 8” focal distances at 7mAs and 0.2 s
  (7mA * 02s = 1.4 mAs) 1.4 mAs/ exposure.
• It takes 417 mAs/1.4 mAs = ~298 exposures
  1/3 of the TED is delivered with ~298 intraoral dental exposures

Question 22

Linear Non-Threshold Curve - 1

Answer 22

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

Question 23

Linear Nonthreshold Curve -2

Answer 23

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

Question 24

why are there many proposed dose response curves?

Answer 24

no data available at lower doses makes it hard to predict a line of best fit.
There is considerable controversy over the most appropriate model for determination of human radiation risk at low doses.

Question 25

SELECTION CRITERIA FDA/ADA

Answer 25

• Imaging requires justification
• Need a specific question or a diagnostic task where radiographs will provide unique information not readily available from other diagnostic means
• An initial clinical exam is required to make this assessment

Question 26

What Has Dentistry Done to Reduce X-Radiation Dose?
* papers?
* collimination?
* selection?
* sensors?
* timers?
* sheilding?
* aprons?
* focal length?

Answer 26

• AAMR guidelines/papers
• rectangular collimination
• selection criteria
• high speed sensors
• microtimers
• improved sheilding of tube
• thyroid collars with Pb equivalent
• increased focal length

Question 27

Patient Shielding During
Dentomaxillofacial Radiology recommendations

Answer 27

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