Verification

Question 1

What are systematic errors?

Answer 1

Occur as a result of incorrect target outlining and data transfer between planning and actual trt set up.
May be caused by incorrect design, marketing or positioning of immobilisation.

Question 2

What is the effect of systematic error?

Answer 2

Shift dose dis with reference to its PTV

Question 3

What are random errors?

Answer 3

Daily variation in treatment sent up and anatomical changes between trt.

Question 4

Effect of random error

Answer 4

Blur the edges of PTV
Smaller high-dose volume
Broader penumbraw

Question 5

What is the geometric verification for prostate?

Answer 5

UCLH - Daily CBCT

Tolerance of 3mm

5mm - nodes

If accurate within 3mm, weekly checks done

If less greater than 5mm, accuracy ensured before next trt

Question 6

What are the action levels for prostate?

Answer 6

Fraction 1 - image all fields using opened fields. Reduce image borders to avoid OAR, assess and correct for gross errors

Fraction 2 - image orthogonal set and assess each image against tolerance levels set and correct gross errors for each fraction

Fraction 3 - if correct set up confirm by repeat imaging and calculate new overall average set up error and correct values greater than action levels.

Weekly - image orthogonal set if set up error greater than tol, repeat imaging

Assess and correct based on new average set up errors

If result is within tol then no action level.

Tol is less than 2mm