3D-CRT Breast Cancer Planning
Tips and Tricks
Bedn, V.
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
3D-CRT Obsolete or not?
There are more advanced techniques than 3D-CRT, but 3D-CRT
has some advantages:
Availability and price
Forward planning - better plan understanding
Easier plan verification
You can not compare an average 3D-CRT plan with good VMAT
plan, but in many cases, a good 3D-CRT plan can be as good
as average VMAT plan (or even better)
Maybe 3D-CRT is obsolete, but its still alive and it can do a
great job for us;)
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Radiotherapy planning basics
Every percent and every millimeter is important
1% of irradiated volume means up to 3% TCP/NTCP
What happens, if we would take
away just 1mm from this tennis
ball?
We will decrease its volume by
10% !!!
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
3D-CRT of breast cancer
In 3D-CRT of breast cancer, we hardly find something special
(and useful), but we may (or should):
Really know our linac and TPS
Get most of every beam we use
Get most of every MU we irradiate
Save every millimeter we can save
Save every percent we can save
Use proper plan normalization
Think about plan robustness and technical realization
and our plans will be better
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Field arrangement
Basic field geometry is always the same
Using half beams (1 isocenter) or beam matching (2 isocenters)
Two tangential fields for breast
Two fields for axilla and supraclavicular nodes
And some low-weight fields for dose distribution improvement
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
The competition case
Used equipment:
TPS Eclipse 8.6, AAA algorithm
Clinac 600C (X 6MV), MARK52 MLC
Following the competition criteria (1 isocenter), I was not able to
use my MLC because of insufficient range, so I used blocks
In practice, I use 2 isocenters and non-coplanar fields as a
simple way to extend my MLC range
You can use standard 80 or 120 leafs MLC with similar results
as I have got with blocks, just use the MLC instead of blocks
I dont think the presented plan is a good plan, it is just a plan
that tries to meet the competition criteria and there are no
criteria for plan robustness, dose to larynx, integral dose,
however you can simply modify it to meet your own criteria
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Isocenter position
Find out the plane, where PTV shape changes significantly
Usually few millimeters below supraclavicular nodes
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Tangential fields
Gantry angles minimize irradiated lung volume
These lines should
be matched
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Tangential fields
To find optimal gantry angles, show only PTV and left lung in BEV
G120 G125 G130
G300 G305 G310
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Supraclavicular and axillar fields
Show OARs (structure outlines only) in BEV
Find the best gantry angles, minimize irradiated volume of OARs
G305 G125
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Completing the plan
Add some wedges
Usually 15 for breast tangential fields
Wedges for supraclavicular/axillar fields are strongly dependent on
gantry angles
Adjust field weight
Just by your experience
Choose the right plan normalization
In this case, D99%=95% means 15 points for you;)
Calculate the dose distribution
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
First look to dose distribution
Oh no, its terrible ;(
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
What to improve?
Volume Points Points Criteria full no
total points points
PTV 45 15 D99% >95% 90% 15
5 D95% >100% 90% 4
5 D50% <104% 108% 5
5 D0,3cc <110% 114% 2
5 HI (D1%-D99%) <8% 20% 1
5 Conf. num. >0,9 0,6 0
5 Global max. inside CTV_LUMP. 0
Lung L 19 5 Mean <18% 30% 0
5 V40% <15% 20% 0
5 V20% <30% 40% 0
4 V10% <50% 70% 4
Lung R 5 5 V10% <3% 6% 5
Heart 20 10 mean <8% 10% 0
5 V30% <15% 20% 5
5 D5% <40% 50% 0
Breast Right 6 2 D0,3ccm <4% 6% 2
4 D5% <4% 6% 4
Spinal Cord 5 5 D0,03ccm <16% 40% 5
Sum 52
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Decreasing dose to the left lung and heart
In the end, we will precisely fit collimator and save few percent
Sometimes, you can save a little volume of irradiated heart and
lung using asymmetric arc field
The more asymmetric this arc is, the more concave shape of
dose distribution you get (but there are usually hardware limits)
Balance the field weight to get uniform dose distribution
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Plan consolidation
Look at the plan, and
yes, there are 2 fields with the same gantry angle and the similar
weight. You can merge them and save some MU, treatment time
and scattered radiation dose
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Homogeneity improvement
Use support fields with low weight (~12% of main fields)
If the support fields have the same gantry and collimator angle
and beam modifiers (wedges) as main fields, these support
fields would not induce significant treatment time prolongation
and therapists work
Using persistent dose in Eclipse allows you to see the dose
while editting fields in BEV excellent feature
Set required dose range you would like to view (e.g. 95% -
110%)
You can add the dose where you need to
Add another support field, balance the weight of fields again and
again
Shape the dose distribution as you like, take advantage of
intentional inhomogeneity
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Homogeneity improvement
Effect of the support field
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Conformity improvement
Carefully look all fields and shield every irradiated millimeter you
dont need to irradiate
Add dose
here
Remove
dose here
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Next dose to OARs reduction
Compromise between dose to OARs and PTV coverage
Dont shield here you just
shield PTV and minor volume
of lung
Shield here you shield
remarkable part of lung and
heart at once
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Plan revision
Carefully view the dose distribution
Find and fix weak points
Review, weight and shape field by field
Think about next improvement
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Final plan
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Final plan
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Final plan
Volume Points Points Criteria full no
total points points
PTV 45 15 D99% >95% 90% 15
5 D95% >100% 90% 4.9
5 D50% <104% 108% 5
5 D0,3cc <110% 114% 5
5 HI (D1%-D99%) <8% 20% 3.7
5 Conf. num. >0,9 0,6 0.4
5 Global max. inside CTV_LUMP. 5
Lung L 19 5 Mean <18% 30% 0
5 V40% <15% 20% 0
5 V20% <30% 40% 1.8
4 V10% <50% 70% 4
Lung R 5 5 V10% <3% 6% 5
Heart 20 10 mean <8% 10% 10
5 V30% <15% 20% 5
5 D5% <40% 50% 5
Breast Right 6 2 D0,3ccm <4% 6% 2
4 D5% <4% 6% 4
Spinal Cord 5 5 D0,03ccm <16% 40% 5
Sum 80.8
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Final plan
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Final plan
Svet zdravia, a.s., Department of Radiation Oncology Rimavsk Sobota, www.radioterapia.szm.com
Thank you for your
attention.
