Miscellaneous Flashcards
1 Gy in rad
100 rad
1 Sv in rem
100 rem
Roentgen
2.58*10^-4 C/kg
what is in NCRP 116?
• Similar to ICRP 103, which is more recent anyway (2007 vs. 1993)
• Guidance for emergency occupational exposure: only actions involving life saving justify acute exposures significantly in excess of annual effective dose limit.
o Older workers with low lifetime accumulated effective doses should be chosen when possible
o For equivalent doses > 0.5 Sv to a large portion of the body in a short time, workers need to understand not only the potential for acute effect but also the substantial increase in lifetime cancer risk.
what is NCRP
National council on radiation protection and measurements
NCRP 107 is on what?
ALARA for medical and dental personnel
is it enough for licensee to just respect dose limits?
not per ALARA- licensee must do all they can to reduce dose within reason
what happens if licensee demonstrated that occupational doses are unlikely to exceed 1 mSv/yr and public doses 50 uSv/yr?
CNSC may decided ALARA assessment is not required
-motivation for 1 mSv is because background variation is ~ 1 mSv
limitations of personal dosimeters
- may be orientation or energy dependen
- accuracy of readout
- relationship between reading and effective dose
MDL
minimum detectable limit
mean annual whole body dose of all medical workers in 1980 in Ontario
0.6 mSv/yr
what 2 things does detriment take into account?
probability and severity
collective dose equivalent
product of dose equivalent in whole body or any specified organ and number of members in exposed group
NIRL
negligible individual risk level = annual individual dose equivlanet below which the average excess risk of health detriment is so low as to make unwarranted any further effort to reduce exposure = 0.01 mSv/y
IRR
individual reference range = range of dose equivalent values that, if exceeded, automatically triggers optimization activity.
CRR
collective reference range = bounds of CRR are 1 and 2 SD above mean collective dose equivalent. Is collective analog of IRR
How do you choose IRR and CRR?
Average annual dose equivalent = 0.55 mSv, average of monitored employees that receive at least one measurable reading during the year = 0.9 mSv. Maximum yearly dose equivalent received by any individual = 3.75 mSv. Average yearly collective dose equivalent= 5.5 person-mSv.
Choose IRR from 0.55 to 1 mSv per quarter and CRR from 1.5 to 1.9 mSv per quarter (doses are typically reviewed quarterly)
most significant significant souce of exposure for RO pesonnel
brachy without remote afterloader
what happens if xray beam if not collimated to size of image receptor?
must shielf therapy simulation rooms with primary radiation barriers
exposure due to Co-60
head leakage is always present, not just when the machine is on. Exposure to Co-60 head leakage may result in 1 to 2 mSv/year average dose equivalent to technologists working solely with Co-60. The same study noted that technologists working solely with 4 MV and 6 MV linacs never received measurable monthly film badge exposures, but that those working on a 25 MV linac did (due to radioisotopes produced by photoactivation of air and accelerator components)
is the 5 year dosimetry period rolling specific to each worker?
No
first one began Jan 1 2001
limit for total occupational dose
5 * (N-18) where N is age
• Total effective dose received by NEW during full working life should not exceed 1 Sv (assuming 50 working years, this corresponds to 20 mSv/year
nominal risk coefficients and detriment-adjusted risk coefficients for workers and all persons
Detriment adjusted values are smaller because a non-fatal cancer is “less detrimental” than a fatal cancer although it still causes harm in terms of loss of QOL and years of life lost.
- nominal = 17.2 % /Sv for all persons, detriment adjusted is 5.7%/Sv
- nominal = 11.8%/Sv for all working population, detriment adjusted is 4.2%/Sv
-these numbers include cancer and heritable
cancer only= 5.5 and 4.1%/Sv
heritable: 0.2 and 0.1%/Sv
relative risk vs ERR vs EAR
• Relative risk: rate of disease in exposed population divided by rate of disease in unexposed population
• Excess relative risk (ERR): relative risk minus 1 (typically expressed per Sv or per Gy)
• Excess absolute risk (EAR): rate of disease in exposed population minus rate of disease in unexposed population.
o Use when risk of disease does NOT depend on normal rate of occurrence of that disease.