Hybrid Breast Planning

Question 1

Hybrid IMRT - no nodal involvement

Answer 1

• Consists of 4 beams: 2 tangential open fields (ant and post ob) with no wedging and 2 tangential IMRT fields (acts as wedging to smooth dose)
  ROPART: 60% of prescription for open and 40% on the IMRT

Question 2

Why choose hybrid

Answer 2

For swollen breast
In IMRT swollen tissue is shielded out
Open fields allow for contour change, intrafraction and interfraction variation
MUs in IMRT is higher therefore a hybrid allows a balance between 3DCRT low Mus and IMRT higher Mus
Reduce number of segments to make sure DIBH time is 20-25sec. Wedges (smaller ones) increase delivery time

Question 3

ROIs in plan

Answer 3

• External, external plus wax, LT RT Lung, Heart, Breast/chest wall CTV/PTV/EVAL

Question 4

Prescriptions

Answer 4

RO prescribes 40Gy in 16 FRACTIONS
24Gy in 16 fractions to ref point - open plan
16Gy to ROI mean for breast_obj in 16#

Question 5

Overshoot

Answer 5

INF breast overshoot 1.5cm

Question 6

Positioning of open field ref pt

Answer 6

midway between skin surface and lung surface
-approx mid sep
At mid tangent length

Question 7

What to do if there is low coverage

Answer 7

push optimiser, 10mv energy
Move RP
If sep is less than 23, 10mv may not be ideal due to skin sparing
Rotate Colli -> view using DRR and skin render
Set sup and inf jaw to cover PTV

Question 8

How to reduce hot spots

Answer 8

Adjust BREAST_OBJ/CW_OBJ to exclude non-breast areas where
high doses are occurring, e.g. inferior to breast. Re-optimise IMRT
plan
 Decrease uniform dose value on BREAST_OBJ/CW-OBJ. Re-optimise
IMRT plan
 Adjust weightings of OPEN beams or move RP to reduce or move
hot spot
 Consider 10MV, don’t forget skin sparing occurs with separations of
approximately 23cm or less. Can use 10MV on open and 6 MV on
IMRT

Question 9

What to do following completion of plan

Answer 9

Evaluate control points and combine control points that are very
similar (lock weights on segments except those to be combined,
and then delete the unnecessary segment)
 Add ‘Flash’ to Control Point 1 (largest and highest MU) plus any
other CPs that only shield anterior overshoot
 Ensure IMRT beam jaws match Open beam jaws
 Finalise MU rounding
 Re-compute beams
 Position MOSAIQ DP on reference dose isodose line
 Re-label all beams as per departmental protocol

Question 10

How to create overshoot on control points

Answer 10

In the convert window,
Under MLC options
Adjust the skin flash adjustment > shift leaves to 2cm
With control point 1 active, shift the bank of MLCs that is overshooting on each IMRT field then compute beams

Question 11

How many cm of lung could be included

Answer 11

3cm max

Question 12

Beam angles

Answer 12

G125 - PO
G305 - AO
Lt breast

Question 13

Heart shielding

Answer 13

Leads to lack of coverage but reduces heart dose

Question 14

PTV EVAL

Answer 14

Usually only contracted from chest wall but sometimes also from skin surface

Question 15

Why do you cut corners of ptv

Answer 15

Reduce max dose
Decrease dose posterior in NTT
Only cut in IMRT fields so the coverage is still received through open fields in these areas

Question 16

IF 95% line missing coverage what to check instead

Answer 16

Check 93% iso line

Question 17

Mosaiq DP

Answer 17

ICRU dose reporting point
Placed on the reference dose iso line

Question 18

How to create max dose obj

Answer 18

Outside the tangent cut
Use 50% iso dose line of open field to create an ROI - expand and left posterior 1cm