Dose Limits Flashcards
ICRP Occupational Annual EFFECTIVE Dose Limit (Stochastic)
20 mSv/yr, averaged over 5 years, with no more than 50 mSv in any one year
ICRP Occupational Annual EQUIVALENT Dose Limit (Non-Stochastic)
500 mSv/yr (to skin, hands, and feet), except lens of the eye, 150 mSv/yr
ICRP Public Annual EFFECTIVE Dose Limit (Stochastic)
1 mSv/yr (a higher value of effective dose could be allowed in a year provided that the average over 5 years does not exceed 1 mSv in a year)
ICRP Public Annual EQUIVALENT Dose Limit (Non-Stochastic)
50 mSv/yr (to skin), except lens of the eye, 15 mSv/yr
ICRP Control on EFFECTIVE Dose of 20-100 mSv, annual or acute
Consider reducing dose. Controlled by action on exposure pathway (eg. Walls, lead, etc.), radiological emergency reference level.
ICRP Control on EFFECTIVE Dose of 1-20 mSv, annual or acute
For planned exposure situations, individual dose assessment and training (eg. PPE). Controlled by action on source or exposure pathway (eg. Blocks, walls, lead, etc.).
ICRP Control on EFFECTIVE Dose of <1 mSv, annual or acute
Periodic checks on exposure pathway. Constraints for public exposure in planned situations.
NCRP Occupational Annual EFFECTIVE Dose Limit (Stochastic)
50 mSv/yr (excluding doses from natural sources)
NCRP Occupational Cumulative EFFECTIVE Dose Limit (Stochastic)
10 x Age mSv (excluding doses from natural sources)
Occupational Annual EQUIVALENT Dose Limits (Non-Stochastic)
500 mSv/yr to all organs except lens of the eye, 150 mSv/yr (excluding doses from natural sources)
NCRP Public Annual EFFECTIVE Dose Limit, if Frequent (Stochastic)
1 mSv/yr (excluding doses from natural sources)
Public Annual EFFECTIVE Dose Limit, if Infrequent (Stochastic)
5 mSv/yr (excluding doses from natural sources)
NCRP Public Annual EQUIVALENT Dose Limit (Non-Stochastic)
50 mSv/yr to all organs except lens of the eye, 15 mSv/yr (excluding doses from natural sources)
Embryo / Fetus Monthly EQUIVALENT Dose Limit (there are no EFFECTIVE Dose Limits)
0.5 mSv/month
NCRP Negligible Annual EQUIVALENT/EFFECTIVE Dose
0.01 mSv/yr (excluding doses from natural sources)
Mobile radiographic equipment requirements
Exposure cord must permit the operator to stand at least 6 ft, exposure switches NEED NOT be the two-stage type, a lead apron should be carried with the unit and worn, the radiographer must alert individuals in the area before making the exposure
Guidelines for the use of protective shielding for gonadal shielding
If the patient has reasonable reproductive potential, when the gonads are within 5 cm of the collimated field
Approximate entrance skin esposure (ESE) for the average anteroposterior (AP) supine abdomen radiograph
300 mrad (or ~3 mSv)
Grid vs. Collimator
Grids are used POST-PATIENT EXPOSURE to reduce blur in images, collimators are used PRE-PATIENT EXPOSURE, thus collimators can reduce dose while grids cannot.
Assumptions about patient x-ray scatter intensity at 1 m?
Intensity is 1/1000th the intensity right before scattering.
NCRP Minimum Lead Apron Thickness Minimum Requirement
0.5 mm Pb
NCRP Leakage Radiation Limit at 1 m
100 mR / hr
Radiation safety in fluoroscopy
- Tabletop radiation intensity must not exceed 2.1 R / min / mA
- Tabletop radiation intensity must not exceed 10 R / min
- In high-level fluoroscopy, tabletop intensity up to 20 R / min is permitted
Primary Radiation Lead Shielding Minimum Requirement
1/16 inch Pb
Use Factor
Fraction of time a particular wall is being irradiated by a PRIMARY beam during scans.
