Non-coplanar and FIF techniques

Question 1

What are Coplanar plans?

Answer 1

Same plane

Transverse (Axial)

Question 2

What are Non-Coplanar techniques?

Answer 2

Occurs when couch is rotated

Question 3

What is the rationale for NCP beams?

Answer 3

When transverse beams would enter or exit through OAR

Non IMRT solution with minimal MLC and time

Potential for lower dose to NTT

Question 4

What are some considerations for NCP beams?

Answer 4

Minimum angle between beams

Avoids overlapping high dose regions

Best homogeneity with maximal separation of beams

Question 5

How can you determine angle choices for NCP beams?

Answer 5

Evaluate dose distribution without wedges

Decide what wedge to use and size

Use automated optimisation tools to determine appropriate combinations

Question 6

What is a compound angle?

Answer 6

Arises when NCP fields don’t share sides of the target

-recommend rotating collimator to match fields may compromise efficiency

Question 7

What are potential issues with compound angles?

Answer 7

Uneven coverage of the target

Wedge orientation

Question 8

Why is the couch and gantry rotated in breast planning?

Answer 8

To minimise lung and contralateral breast doses for concave breasts.

Question 9

Beam orientations for breast planning NCP

Answer 9

LAO: Couch 340 –345, Gantry 55-65 degrees
RPO: Couch zero, Gantry200-230 (Part PTV)
C Post: Couch zero, Gantry 180 (Part PTV)

Question 10

Why is the couch and gantry rotated in prostate planning?

Answer 10

Angles can avoid femoral heads. penile bulb or rectum

Question 11

What are some beam arrangments used?

Answer 11

7 field Axial beam

5 field coronal crossfire

7 field coronal crossfire

Question 12

What is a common site for NCP?

Answer 12

Brain

Left lat- G90, Couch 0

Right
lat- G270, Couch 0

Sup oblique-G80-100, Couch 290-310

RT/LT Ant obliques -Beware of RT/LT Ant obliques

Question 13

Why is it important to spare the hippocampus?

Answer 13

located on the floor of each lateral ventricle of the brain, thought to be the centre of emotion, memory, and the autonomic nervous system

Question 14

What are some considerations for NCP?

Answer 14

• Workflow issues
• Chance of making error increases

-Safety: Gantry clearance (REV)

Question 15

What are the REV benefits?

Answer 15

Assist is checking wedge placement

-Assist in checking collision gantry

Question 16

What is the benefits of cyberknife treatment

delivery?

Answer 16

• Robotic arm
• Treat tumours with multiple NCP beams
• Stereotactic treatment delivery
• Various tumour types

Question 17

What is FIF techniques used for?

Answer 17

• Contour shielding
• Contour boosting
• Concomitant Boost

Question 18

What is the rationale for FIF?

Answer 18

Useful where high dose regions needs to be somewhere that a wedge cant position

-Series of subfields

Question 19

What does the summing of all the subfields equal?

Answer 19

rough wedge distribution

Question 20

What are the considerations for FIF?

Answer 20

Ensure RP is not occluded in either of the field

-Keep weighting of smaller fields small

Question 21

What are some shielding methods?

Answer 21

Jaw shifts
MLC fields
Combination of the two

Question 22

What is the Jaw shielding approach?

Answer 22

Optimise weightings wedges to move max dose into the sup/inf plane

Then move inf/sup jaw to shield out hot region

Question 23

How is the MU affected in FIF and wedged techniques?

Answer 23

FIF requires less MU than wedges

However when used as boost more MU may be required

Question 24

What is a concomitant boost?

Answer 24

a subfield with a separate prescription

Question 25

How can FIF affect forward planned IMRT?

Answer 25

change intensity across the field