managing rad risk Flashcards
Estimated Number of CT Scans Performed Annually in the US.
The most recent estimate of?
62 million CT scans in 2006.
occupational MPD
5.0 rem/year (5,000 mrem)
50 mSv
non-occupational MPD
0.5 rem/year (500 mrem)
5 mSv
how much of total radiation to population does ionizing imaging account for
1/6
have nuclear medicine and CT use increased?
yes, more radiation exposure to public to more than 50% of total exposure
Estimated Organ Doses from Typical
Single Head CT Scan graph
decreased risk with increased age
Estimated Organ Doses from Typical
Single Abdominal CT Scan graph
decreased risk with increased age
what is the typical age for the beginning of a drop in risk associated with ionizing radiation
around 25
age association with risk of malignancy
* Cancer risks decrease with?
* latency periods for solid tumors?
* radiosensitivity? why?
- 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
Effects of Age and Female Gender on Cancer Risk:
*Females < 10 yo,
*20 yo females
*30 yo females
*40 yo females
Effects of Age and Male Gender on Cancer Risk:
Males < 10
*20 yo males
*30 yo males
*40 yo males
ages: 10,20,30,40,50
Pediatric Patients at risk
* Pediatric tissues at?
* Greater life expectancy?
- 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
- Female orthodontic patients in the age group 11-15 who have more than 1 CBCT in 2 years have a risk of?
risk of 71 deaths per million CBCT exposures (median dose of 300 uSv.
- maximum doses of CBCT machines?
- In this small group the risk increases to?
- 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
US dentists may cause ? cases of cancer per year from radiation
Use of rectangular collimation and selection criteria could reduce this to?
- US dentists may cause 967 cases of cancer per year from
- Use of rectangular collimation and selection criteria could reduce this to 237
dangerous trend in ortho
- 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)
Threshold Non-Linear Curve
- 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)
Rad eryhtmea doses
- 250 Rads – Threshold radiation Erythema Dose (TED)
- 500 Rads – Average radiation Erythema Dose
- 750 Rads – Maximum radiation Erythema Dose
1959 exposures
- 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)
2020 exposures
- 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
Linear Non-Threshold Curve - 1
- Dose is proportional to the response
- No matter how small the dose, there is some
damage
Linear Nonthreshold Curve -2
- No threshold
- Minimal damage at first with increased rate
of damage with increased dose
why are there many proposed dose response curves?
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.
SELECTION CRITERIA FDA/ADA
- 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
What Has Dentistry Done to Reduce X-Radiation Dose?
* papers?
* collimination?
* selection?
* sensors?
* timers?
* sheilding?
* aprons?
* focal length?
- AAMR guidelines/papers
- rectangular collimination
- selection criteria
- high speed sensors
- microtimers
- improved sheilding of tube
- thyroid collars with Pb equivalent
- increased focal length
Patient Shielding During
Dentomaxillofacial Radiology recommendations
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
