Imaging with Radiation Flashcards
What four requirements are specifically for Radiotherapy imaging?
Hard, flat couch top
Compatibility with immobilisation devices
Lasers
Geometric fidelity
Why are accurate HU required for RT imaging?
HU can be converted to electron density
Electron density values are used in dose scaling calculations
Therefore it is used for calculating the dose distribution
Why do the relative electron densities change with HU for different imaging sequences?
Different kV is used, therefore there are different levels of attenuation
How are the electron density tolerances calculated?
Find the change in electron density which would result in a 2% dose difference in a plan
What are concomitant doses?
Doses which arise from all the aspect of Radiotherapy
What are the sources of concomitant doses?
Repeat CT scans
Non-treatment fields
Image guidance technologies
What are the requirements for IGRT protocols?
Dose is ALARA
Produces adequate image quality
When would a higher dose IGRT protocol be accepted?
Improved image quality, therefore better localisation of the tumour, ie 4DCT
What three actions are centres expected to do for optimisation?
Set DRLs
Compare doses with local centres
Take part in regional and national audits
What are the aims of optimisation?
Create images of sufficient clinical quality
Ensure dose does not change over time
Keep image quality consistent
Ensure consistent performance by trained operators
How does the imaging panel type effect the dose to the patient?
The more efficient the imaging panel the lower the dose needed to produce images of the required quality, therefore a lower dose is needed
What are the steps required for optimising an imaging protocol?
Can the field of view be reduced?
Can the mAs be reduced?
How often is imaging needed?
