Lecture 6 Flashcards
(28 cards)
What’s the purpose of reject analysis
Asses unnecessary dosage of departments
Establish baseline for quality assurance
Help rectify if facility is providing unnecessary exposure
What methods are there for rejection analysis?
Methods depend on the needs of individual department
Can be:
- counting rejected images
- analysis by room
- analysis by reason ie. radiologist opinion
- analysis by reason and room
Briefly outline the procedure of reject analysis
Aim and method informed to staff (radiologist, radiographer, support staff)
Length of time
Number of people supervising
Design reject sheet
All radiographers given reject sheets
Count rejected within intervals
Collect sheets
Find number of examinations done on images performed
Then use results to help rectify technique
What’re the reasons for reject?
Over exposure or under Positioning Blur Collimation Processing equipment Artefact in ROI Miscellaneous (unknown fault)
What does the effective dose represent?
mSv
Shows the whole body dose and determines the somatic effect of radiation
Explain what’re DRLs
Measured values to be used to minimise any excessive radiation exposure to patient
Helps limit unnecessary variation in pt doses
They aren’t thresholds, so flexibility is permitted to allow higher doses for a better clinical judgment
Ie. chest DRL = 0.3 Gy but can be increased if pt is thick in order to get good image
Not to be used for individual patients or as trigger levels
Why’s the implementation of DRLs important?
Allows a comparison/standard that imaging centres can use to not allow unnecessary doses
Can help identify reasons for over exposure and determine strategies
How can we tell that a imaging clinic is doing an overwhelming amount of unnecessary exposing?
Median value is considered to be consistently exceeded when local median value > local, national, or regional DRL values
What’re the 2 broad groups used in the measurement of dosimetric quantities?
Application specific
Risk related
Explain what is application specific dosimetric quantity
Practical dosimetric quantities obtained from direct measurement tailored to specific situations of modalities
Eg. Incident air karma, entrance surface air Kerma, air kerma (area product), CT air kerma indices
Explain what is risk related dosimetric quantities
Estimates radiation detriment or risk (measure absorbed dose)
Eg. Organ dose and mean glandular dose in mammography
What’re DRLs quantity?
Application specific quantities used only (ie. incident air kerma, ESAK, AKAP)
Should be relevant to the imaging modality being evaluated specific study performed, patient size
Risk related quantity aren’t used as DRLs
What’re the drl quantities used in planar radiography?
To simplify assessment of proper use of collimation, especially paediatrics we use ESAK, IAK, AKAP&
When is it useful to use phantoms for measurement?
Do not use for drl measurement
Controlling technical parameters (the system)
Comparisons of system at different times
To optimise individual components or the whole system
What’re the limitations of using phantoms for measurement?
Doesn’t estimate average dose for a given pt population
Ie. weight, size
Therefore, doesn’t show variation in real clinics in terms of patient size and composition
No info on intra or inter operator variability in technique factor (ie. same parameters always used therefore can’t be used to find DRLs)
Explain what makes a patient measurements useful ?
Accouts for variations in equipment performance, operator technique, patient related characteristics
Increase Sample size of pts to find median and/or average calculated
Therefore allowing comparison at local, regional, national distribution, image quality might be affected negatively
In what ways can drl quantities be collected?
Surveys
Registries
Or other automated data collection methods
What exactly occurs when conducting drl surveys?
Calibrate all dosimeters used for patient dosimetry and traceable to primary or secondary labs
Is the drl quantity accurate from the system that was used to produce it? Medial physicists check this
Drl quantities obtained for the most frequent type of examinations
Not done for radiation therapy
Used for imaging for treatment planning, treatment rehearsal, and patient setup verification in radiotherapy
Collect data for > 20 and >30 for flurocospy and ct
Doses measured using DAP (dose area product)
Where should the sample of DRLs be collected from for a survey?
Weight standardisation for adults if sample is < 50 pt.
National surveys and registries should include medium and large sized facilities
Large countries = survey Random selection of small proportion of facility
explain how DRLs are established mathematically For routine plain X-ray examinations
Select dose data of 20 pt (60-70kg) or 50 pt. If weight info not provided
Measure DAP for each projection
Find median DAP of all facilities
Calculate 75th percentile of all median values which will be our DRL
How’re DRLs obtained for CT?
Instead of measuring the DAP of examinations, we do CTDIvol (CT dose index volume) and DLP (dose length product)
Find median of both variables for each facility
Then calculate the 75th percentile of the median values
Why’s there variability amongst facilities?
Different equipment used
Varied patient size
Differnt departmental protocols ie. methods
How is a DRL value even set for an imaging task?
Value should adhere to good image quality
Data for drl values must be collected from similar procedures across all facilities
Specify views included and clinical task associated with the procedure
What’re the types of DRLs
Typical values: 1 facility with several rooms or small number of facilities or single facility linked to a new technique
Local = X-ray rooms within few facilities (eg. With > 10-20 rooms) in local area
National = representative selection of facilities covering an entire country
Regional = countries within region without a relevant DRL or when national drl is higher than regional value
