Breast Hybrid

Question 1

What is IMRT?

Answer 1

Uses beams with varying intensity which conforms high dose to target volumes. Enables dose escalation and improved tumour control.

Question 2

What is Forward-planning segmental IMRT?

Answer 2

Extension of 3D conformal beam, intensities are modulated using physical or dynamic wedges, asymmetric jaws and MLC’s.

Question 3

How do you design modulated fields?

Answer 3

process that begins after 3D-conformal plan has been computed and evaluated.

–> Beam weights, directions and intensities can then be modified for optimal plan.

Question 4

What is a control point?

Answer 4

A point during treatment where the beam changes.

Gantry, MLC positions, jaw position, wedged and MU/weight

Question 5

What is a segment/MLC control point?

Answer 5

A control point that only allows changes in MLC leaf positions, jaw positions, wedge and MU/weight.

Question 6

What is segmental IMRT?

Answer 6

Uses fixed segments/subfields to create the intensity modulated dose distribution.
–>Beam segments are usually created using static MLCs.

Question 7

What can you do instead of creating multiple FIFs?

Answer 7

You can modulated beam intensity by adding control points to a beam

Question 8

OAR, Quantec tolerances and toxicity end points for breast planning?

Answer 8

Heart- V25 <10%-pericarditis

Lung V20% less then 30%- Symptomatic pneumonitis

Question 9

Why use forward planning IMRT over inverse planning IMRT?

Answer 9

Less time consuming
reduced max dose
dose homogeneity improves
Reduces lung dose

Disadvantage of Inverse planning
–>control point approach >different QA requirements