Imaging with Radiation

Question 1

What are the technical challenges of imaging bariatric patients?

Answer 1

May not fit into bore of scanner
Field of view may not cover patient which results in incomplete patient surface data = large source of uncertainty
Couch load limit may prevent them from being imaged or treated
Image quality is poorer = increase kV or mAs if xray tube not reached limit.
Overriding densities from artefacts becomes time consuming for dosimetrist

Question 2

What features are required for radiotherapy imaging?

Answer 2

Hard, flat couch top for reproducible position
Compatibility with immobilisation devices
Lasers for patient positioning

Geometric fidelity

Question 3

What is required to use a CT scan for planning?

Answer 3

HU density to electron density curve

Question 4

What is the equation to calculation a Hounsfield Unit?

Answer 4

HU = 1000 x [ ( u - u(water) ) / ( u(water) - u(air) ) ]

Question 5

What is the concomitant dose?

Answer 5

It comes from all exposure from RT other than the treatment exposures, such as: verification imaging, re-planning CTs, image guided technologies.

Question 6

How can concomitant dose be instantly reduced?

Answer 6

Determine whether 2D imaging is acceptable; is 3D information necessary?
Determine the necessary frequency of imaging.

Question 7

What are the aims of image optimisation?

Answer 7

Images acquired and presented are consistently of sufficient quality for the clinical task
That the dose burden does not change over time
The consistency of image quality
The consistent performance of the clinical task by trained operators

Question 8

Which factors affect patient dose?

Answer 8

Image volume
Irradiated volume
Image acquisition parameters (eg kV, mAs)
Detectors & their energy absorption efficiency

Question 9

When viewing a similar image range (width/length), which type of scan irradiates a larger volume: CT or CBCT?

Answer 9

CBCT, if volume reduced, image range is reduced.