Patient dose in diagnostic radiology Flashcards
What value is typically calculated to determine an individual patient dose estimate (e.g. for an incident)? What would be calculated in an ideal situation?
- Effective dose.
- Dose to radiosensitive organs.
Why do patient size and technique used need to be considered when determining an individual patient dose estimate (e.g. for an incident)?
Standardised factors/models are typically used to determine patient dose/risks. They may need to be corrected for patient size and technique used.
What considerations should be taken into account when using radiography dose calculation software?
- Ensuring correct organs are within primary beam.
- Values relative to DAP generally more accurate than those relative to ESD due to the inclusion of field size.
- Most software assumes standard size patients.
- Consider uncertainties when interpreting results.
- May need software amendments to adapt to ICRP103.
What considerations should be taken into account when using CT dose calculation software?
- Checking of technique data sent (e.g. CTDI_vol for series or exam).
- Positioning relative to organs rather than scan length.
- Over-ranging.
- Use of QA values.
How has the trend in patient doses for radiography and fluoroscopy changed over the years? Why is this? How does this differ for CT and why?
- Dropped quite quickly initially but is now beginning to level off.
- Dose awareness, technologies and optimisation techniques have been improved.
- Doses have slightly increased over the years for CT. This is due to more complex examinations being carried.
What difficulties are associated with determining NDRLs for CT?
CT examinations for the same region can vary a lot depending on the clinical indication.
Why is it difficult to create DRLs for paediatric examinations?
Large variations in paediatric patient size make it difficult to get reasonable sample sizes.
How is population dose from medical exams determined?
- ESD/DAP from a national survey.
- Conversion to effective dose using standard factors.
- Exam frequency from national statistics.
- Above to values combined to give estimate of average dose to member of UK population.
- Risk factors from ICRP.
What are the top two medical examination contributors to UK dose?
- CT.
- Interventional radiology.
What does risk from diagnostic radiology exams depend on? Where can risk factors be found?
- Exposure.
- Age.
- Sex.
- HPA and BEIR VI data.
When might detailed dose risk assessments be required?
- Risk benefit analysis for justification.
- Ethics submissions.
- SAUEs.
- Informing worried patients/relatives.
- Choosing between alternative procedures.
What are some areas of focus for CT optimisation?
- Iterative reconstruction techniques.
- mA modulation (setting reference mAs for adequate image quality).
- Highly sensitive detector.
- Wide beam coverage.
- Active collimation.
- kV modulation.
- Superficial organ dose sparing.
- Avoiding overlapping slices/scan areas.
- Slice width setting.
- Changing settings for paediatric patients.
- QA programmes.
- Patient dose assessments.
What are some areas of focus for radiography/fluoroscopy optimisation?
- Sensitive detector.
- Low attenuation couch tops, grids etc.
- AECs.
- DAP meters.
- Low grid factor.
- Avoid cine fluoroscopy.
- Screening times/radiograph numbers.
- Collimation.
- Last image hold.
- Pulsed fluoroscopy.
- Exclude unnecessary examinations.
- QA programmes.
- Patient dose assessments.
- Patient compression
What are some general optimisation techniques?
- Assess equipment doses, image quality and optimisation features prior to purchase.
- Assess doses and compare with DRLs.
- Assess image quality.
- Step-wise changes in technique and re-assessment of dose.
