Safety Code 35 Flashcards
does safety code 35 apply to denstistry, chiro, podiatry, mammo?
no
they have other safety codes for those
somatic effects vs genetic effects
somatic= changes in exposed individual genetic= gives rise to genetic effects
how are estimates of incidence of cancer at low dose determined?
- cannot b measured
- based on linear extrapolation from relatively high doses
linear no treshold hypothesis
health risk from exposure is proportional to dose
4 main aspects of radiation protection for diagnostics
- jutification for medical exam
- patient is protected from excess radiation
- staff are protected
- general public is protected
who is ultimately responsible for safety of facility?
owner
when does responsible personel investigate exposures received by personnel?
- if exposure is higher that usual dose received by that person
- > 1/20 of dose limit for radiation workers
when must staff wear personal dosimeter
-if they are likely to receive a dose in excess of 1/20 of dose limit for radiation worker (i.e. 1 mSv) (i.e. occupationally exposed person)
o CNSC Radiation Protection Regulations says that personnel dosimetry is required for NEWs who have a reasonable probability of receiving an effective dose greater than 5 mSv in a one-year dosimetry period
HL7
health level 7
standard for exchanging information between medical information systems.
DICOM
digital imaging and communications in medicine
general requirements for diagnostics
- x-ray room cannot be used for more than one radiological investigation simultaneously
- unless essential, everyone leaves room when irradiation comes on
- personnel should keep away from x-ray beam
- irradiating someone for traning or evaluation is not allowed
- all personnel must use available protective devices
- workers who are likely to receive > 1/20 of dose limit must be declare radiation workers and wear personal dosimeter
- personal dosimeters must be worn and stored according to recommendations of dosimetry service provider. When a protective apron is worn, personal dosimeter must be worn under the apron. If extremeties likely to be exposed, additional dosimeters should be worn at those locations
- personal dosimetry records must be maintained for lifetime of facility
- female operator must notify employer of pregnancy
- if weak persons need support, holding devices should be used (not staff)
- all entrance doors to xray room should be closed while patient in the room and during exposure
- energized xray machines must not be left unattended
rules regarding mobile x-rays
- only use if needed
- direct xray away from occuppied areas
- operator must not stand in front of direct beam and must be > 3 m away from x-ray tube unless wearing PPE or behind leaded shield
- residual charge must be fully discharged before unit is unattended
requirements of radioscopy
-all persons with possible exception of patient must wear leded apron (shields and curtains are not enough)
one of greatest sources of exposure to personnel in radiology
angiography
requires the presence of a considerable number of personnel close to the patient, radioscopy for extended periods of time and multiple radiographic exposures
recommendations for angiography
- use [protective devices such as shielded drapes etc
- The patient is the largest source of scatter radiation. To avoid this scatter, operate the equipment with the tube under the patient and, if the tube is horizontal, stand on the side of the image receptor.
- PPE (including glasses) and dosimeters must be worn
- personnel not required right by patient should stand behind shields
largest source of scatter radiation in angiography
patient
when is risk of pregnancy small? (for pelvic tests)
10 days following menstruation
recommendations for pregnant or potentially pregnant women
Only essential investigations should be taken in the case of pregnant or suspected pregnant women.
When radiological examinations of the pelvic area or abdomen are required, the exposure must be kept to the absolute minimum necessary and full use must be made of gonadal shielding and other protective shielding if the clinical objectives of the examination will not be compromised.
If a radiological examination of the foetus is required, the prone position should be used. This has the effect of shielding the foetus from the softer X-rays and hence reducing the foetal dose.
Radiography of the chest, extremities, etc., of a pregnant woman, for valid clinical reasons, should only be carried out using a well-collimated X-ray beam and with proper regard for shielding of the abdominal area.
xray beam size limit
size of image receptor or smaller
considerations to ensure patient exposure is kept to minimum
- use of an anti-scatter grid or air gap between the patient and the image receptor;
- use of the optimum focal spot-to-image receptor distance appropriate to the examination;
- use of the highest X-ray tube voltage which produces images of good quality;
- use of automatic exposure control devices designed to keep all irradiations and repeat irradiations to a minimum.
what should you do before taking long series of images?
check the first one to ensure correct setup
difference between radioscopy and radiography
radiography is an off-line, static examination technique, while radioscopy is a dynamic examination technique with the potential for on-line examination and process control.
radioscopy is more dose- only use when necessary
when should cinefluorography be used?
- when absolutely needed
- produces the highest patient doses in diagnostic radiography because the X-ray tube voltage and current used are generally higher than those used in radioscopy
recommendations for angiography
- shield eyes and thyroid if possible
- minimize irradiation time
- use more tube filtration (reduce low E xrays)
- use lower time frequency in pulse radiography
- produces the highest patient doses in diagnostic radiography because the X-ray tube voltage and current used are generally higher than those used in radioscopy
- in children and small adults, removing grid will reduce dose
- magnification may increase dose to patient
- use automated injection if possible
- if procedure is long, reposition tube so that same area of skin is not exposed to xray beam
- for each interventional procedure, document images, radioscopy time, air kerma rates, and resulting skin doses
what ia angiography
Angiography is a type of X-ray used to check blood vessels.
Blood vessels do not show clearly on a normal X-ray, so a special dye needs to be injected into your blood first. This highlights your blood vessels, allowing your doctor to see any problems. The X-ray images created during angiography are called angiograms.
reducing dose in CT
-reduce number of slices and overlap b/w adjacent scans as much as possible given quality required
factors for reducing dose to sensitive tissues
- correct collimation of x-ray beam
- examine kids and adolescents really if only necessary..
- use gonads shields if clinical objectives not compromised, patient is of reproductive age, gonads aer within or near beam
- use proper technique
- maintain sensitivity of imaging system
diagnostic reference levels
for typical procedures, the difference in radiation doses can be as wide as a factor of 50 to 100
- reference levels to help optimize techniques, rather than max dose limits
- better control of patient exposure to x-rays
- AVERAGE of population should meet thiese targets, not necessarily each patient
what are DRLs based on?
CTDIw
- at least 10 patients for sample size, ~ 70 kg
- preferable to use phantoms
-measure entrance dose with TLDs, dose-area-product meters
weekly dose limit for operator for diagnostics
0.4 mSv/week
where should control booth be located?
whenever possible, such that the radiation has to be scattered at least twice before entering the booth
typical workloads for xray facilities
cardiac angio- 4800 mA min/wk other vascular angio- 2000 mAmin/wk chest radiography - 100 mAmin/wk other radiography- 320 mAmin/wk radioscopic- 400 mAmin/wk
use factor for ceiling for diagnostic x-ray
1/16
not routinely exposed to direct radiation beam
assumptions in NCRP 147 for shielding calcs
- The attenuation of the radiation beam by the patient is neglected.
- The incidence of the radiation beam is always perpendicular to the barrier being evaluated.
- The calculation does not take into account the presence of materials in the path of the radiation other than the specified shielding material.
- The leakage radiation from the X-ray equipment is assumed to be an air kerma of 0.876 mGy h-1.
- The minimum distance to the occupied area from a shielded wall is assumed to be 0.3 m.
storage for radiographic film
< 0.1 mG over stored period of film
-Once films are loaded into cassettes, radiation exposure levels should be less than 0.5 µGy and the resulting increase in the base-plus-fog should be less than 0.05 O.D
control booth is secondary or primary barrier?
shpuld be secondary as xray should never be directed to control booth
shielding for CT
only secondary
doesn;t rely on W
use NCRP 147
what regulations must all new, used, and refurbished medical x-ray equioment and accessories abide by?
Radiation emitting devices act
Food and Drugs Act
x-ray tube shielding requirement
- **1 mGy/h at 1 m **away from focal spot when operated at max energy input in 1 hour
- 20 uGy/h at 5 cm from any accessible surface when equipment is not in loading state
x-ray beam filtration requirements
There must be radiation-absorbing filters that provide a degree of attenuation such that the first Half-Value Layer (HVL) of aluminum is not less than the values shown in Table 8 for a selected X-ray tube voltage
- 5 mm for 70 kV
- 3 mm for 120 kV
coefficient of variation
ratio of standard deviation to mean value
what does irradiation switch require?
continuous pressure by operator for entirety of exposure
CTDI100
required for CT
–50 mm to 50 mm, divided by number of sections X thickness
at what locations must CTDI 100 be provided?
- axis of roratio of phantom
- at 0, 90, 180, 270 degrees at 1 cm interior to phantom
CT required info
- CT conditions of operation
- dose info for head/image in terms of CTDI100- has to encompass range of operations that can be done on CT
- dose profile in centre location of dosimetry phantom
- noise
- contrast scale
- MTF
- thickness at centre of imaging section
- sensitivity profile at center of imaged section
- CTDIw
- DLP
contrast scale
(ux-uwater)/(CTx-CTwater)
about 2 X 10^-4 /cm HU
CTDIw
1/3 CTDI100 (center) + 2/3CTDI100(peripheral)
DLP
dose length product
DLP = CTDIw X slice thickness X number of slices in sequence
max OD from bas material and film fog
0.3
PACS
pictures archiving and communication system
what is teleradiology
electronic transmission of radiological images from one location to another for the purposes of interpretation and/or consultation
protective lead apron requirements for different xray kV
- 0.25 mm for 100 kV or less
0. 35 mm for 100150 kV
protective equipment recommended for interventional procedures
- full wrap-aroud Pb gowns with 0.5 mm in front and 0.25 mm in back
- thyroid shields with 0.5 mm Pb
- leaded glasses if scatter to eyes is approaching limit
protective gonad shields for patients
> 0.25 mm Pb
0.5 mm for 150 kVp
protective gloves Pv thickness
0.25 mm
how often is protective equipment tested for integrity?
yearly
Pb thickness of ceiling mounted acrylic screens and moveable shields
0.5 mm Pb
after you make changes to xray facility (barriers, equipment modification), do you survey it?
yes
why do we do periodic surveys?
- detect problems due to equipment failure, or long term trends
- frequency depends on type of facility
considerations for disposal of xray equipment
-assess if hazardous materials (ex. polychlorinated biphenyls), and Pb may be in xray tube housing
4 steps included in establishing QA procedures
- make sure equipment is operating properly
- assess the baseline performance
- use a reference test image to evluate image quality
- determine action levels- acceptable vs unacceptable results
how often is film processor function evaluated?
every morning
-includes sensitometric strip processing
pass criteria for sensitometric strip processing
- base plus fog within 0.05 of operating level
- mid densit within 0.15 of operating level
- density different within 0.15 of operating level
criteria for CT number test to pass
CT number of water must be 0 +/- 4 HU
criteria for CT noise to pass
cannot deviate from baseline more than +/- 10% or 2 HU
-The established baseline noise levels in a CT system should not deviate from the manufacturer specified noise value by more than ± 15%
should CT quality tests (ex. noise, CT #) be for both axial head scan and axial body scan?
yes
diameter of ROI for noise test
40% of diameter of uniform phantom image
equation for CT uniformity
CT number in center of image - CT number at periphery
- use 4 peripheral ROIs
- diameter of each ROI should be 10% of phantom diameter
pass criteria for CT uniformity
within 2 HU of baseline
baseline must be within 5 HU
how to assess DSA performance?
use phantom with image quality test objects
what should retake rate be?
<5 %, not including QA films
test patterns you can use to test electronic device performance ?
SMPTE
TG18
how do you measure CT slice thickness
test device with ramps at angle to scan plane
- for thickness > 2 mm, pass criteria is within 1 mm from baseline
- for thickness 1 mm < t < 2 mm, pass criteria is within 50% of baseline
- for thickness < 1 mm, pass criteria is within 0.5 mm of baseline
how to measure CT slice thickness for helical scanning?
- thin disk or bead
- fwhm of senstivity profile as function of z position is slice thickness
how to do calibration of CT # (monthly)
pick same 2-3 cm2 area for water and air
CT number for water should 0+/- 4 HU and for air should be -1000+/-10 HU
how to measure CT linearity
- scan phantom with many known materials
- compare CT numbers to those baseline
- criteria for pass is set by manufactuer
what does SMPTE stand for?
society of motion picture and television engineers
is safety code 35 recommendation or reg?
recommendation
another word for radioscopy
fluoroscopy!
constraint level for pediatric ward
0.3 mSv/yr
x-ray tube shielding must be such that leakage radiation from xray source does not exceed ___ air kerma rate of
1 mGy/h at 1 m from focal spot
can you turn on fluoro if entire beam is not recepted by image receptor?
No, an interlock should stop this
CT low contrast phantom- how low should contrast of circles be compared to background?
< 1 % or 10 HU
radiation output linearity requirement
|X2-X1| 0.1(X1+X2)
- if discrete, then X1 and X2 are two consecutive settings
- if continuous, then X1 and X2 are settings that differ by < 2
what is exposure index?
- indicates relative speed and sensitivity of digital receptor to incident xrays
- measures amount of xray photons that actually reach image receptor in relative image region
how do you test automatic intensity control for fluoro?
The automatic intensity control system is designed to maintain the rate of the X-ray exposure to the image intensifier with changes in thickness and composition of the anatomical region being imaged. Place a dosimeter between a homogenous phantom and the X-ray source. Double the phantom thickness and repeat the exposure. The exposure measurement should be approximately double the first measurement.
viewbox QA requirements
- luminence should be at least 2500 cd/m2
- light output should be uniform within 10%
- light output homogeneity within a bank of viewboxes should be within 20% of mean
- ambient light in reading room < 50 lux
electronic display device performance- what to use as test pattern?
SMPTE
TG18
describe stepwedge
- as it sounds
- When an image of the stepwedge is viewed, a full range of intensities should be seen, from a light grey at one end to almost black at the other
the image of the middle step (assuming a classic eleven step device) should have an optical density of 1.2 or so. If it didn’t, the exposure factors would need to be tweaked.
describe image lag test for fluoro
- view image of rotating test tool
- radioscopic system should be able to visualize a wire of diameter 0.013 inch or smaller
dose limts for technologists in training and students
as per the public (1 mSv /year)
how to best measure dose to fetus?
-TLD on abdomen
2 source rule for diagnostics
same as for linacs
x-ray warning symbol for DI equipment
CAUTION: X-RAYS–ATTENTION : RAYONS X
-either have picture of xray tube in upside down triangle OR radiation trefoil symbol
Gy to R conversion
1 Gy = 115 R
1 R = 8.73 mGy
