Dose Course 2018_Flipping book

Modelling the MLC leaf ends

The difference in radiation field edge and leaf tip position varies with off-axis location

Source plane

x HVL

- x w

0.1

cm

0.05

x

-10 -7.5 -5 -2.5

2.5 5 7.5 10

cm

-0.05

-0.1

-0.15

-0.2

x

x w

x HVL

isocenter plane

Delivery (linac):

lookup table or parameterized correction to set leaf position

TPS

:

same method as used for delivery; or based on direct calculation of 50% transmission

→ potential inconsistency between dose calculations and delivery

21

From Anders Ahnesjö