Stacey Schmidt, B.S., RT(T), CMD

Manager, Medical Dosimetry

CDH Proton Center

CDH Cancer Center

Delnor Cancer Center

Warrenville & Geneva, IL

Simulation, Planning, and Delivery of

Breast/Chest Wall Treatment Using Uniform

Scanning Proton Beam Therapy

2

Course Objectives

After participating in this session, you will be able to:

• Explain the benefit of using protons to treat stage III disease or

previously treated patients.

• Identify patient selection criteria.

• Discuss the simulation process and immobilization device

selection.

• Describe techniques used in treatment planning.

• Demonstrate the dosimetric advantages of Uniform Scanning

(US) proton therapy over photon therapy.

• Illustrate the daily imaging and treatment delivery processes

specific to US protons

What cancer types are typically

treated with protons?

4

Common indications for proton therapy

• Pediatric tumors of the CNS or elsewhere

• Brain tumors

• Spinal cord tumors

• Base of skull chordomas or chondrosarcomas

• Prostate cancer

• Ocular melanomas

5

Less common, yet emerging indications for treatment

with proton therapy

• Lung cancer

• GI cancers

• Head and Neck cancers

• ……and now, Breast cancer

6

Protons for Breast Cancer? Preposterous!

Past roadblocks include:

• Concerns over target movement/reproducibility

• Lack of skin sparing with Protons

• Photons have been getting the job done very well for

years!

These are valid concerns even with improved

techniques. However, it was worth looking into for a

select subgroup of these patients.

Why use protons?

8

Red Journal article from PSI in 2010

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Stage III Breast Cancer patients

The most difficult breast cancer sub-type to treat with traditional x-

ray/photon radiation therapy, due to the inclusion of axillary,

supraclavicular, and internal mammary lymph nodes.

These photon plans

are generally not very

homogeneous, and include

significant dose to the

Ipsilateral lung and heart

(particularly left

sided patients).

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Retreat Breast Cancer patients

These patients have

typically already

received significant

dose to the

ipsilateral lung

and/or heart, and

therefore it is even

more important to

spare excess dose

to these structures.

Selection Criteria

12

ProCure specific selection criteria required for use of

protons in breast cancer patients

• Stage III disease either post mastectomy or

lumpectomy AND require treatment to ipsilateral

supraclavicular, axillary, and internal mammary lymph

nodes

• Or, must have had RT to the same side previously

• Must not have a pendulous breast or metal expanders

in reconstructed implants

• Must be able to lie with arms up or down for

approximately 45 mins

13

Patients can be treated off or on protocol

• All patients treated so far have been on our Registry

protocol. PCG – Reg – 001

• Patients have the option to enroll in the PCG cardiac

sparing BRE008 and be treated on protocol. These

patients are required to start txmt 9 weeks after

surgery or 8 weeks after the initiation of

chemotherapy. They must also have a CT

Angiography study, which is used to help contour

specific cardiac vessels for dose reporting.

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Patients can be treated off or on protocol

The Simulation Process

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Gantry or Inclined Beam treatment room?

• Before selecting the appropriate immobilization

device, the determination must be made whether or

not the patient will be treated on the gantry or in one

of the inclined beam treatment rooms.

• Differences:

– Gantry room has most flexibility with treatment angles

– Inclined beam room has fixed gantry angles of 30 or 90

degrees, but our technique for this room allows for most

enface setup.

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Gantry

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Incline Beam Line

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Gantry setup

Patient must be positioned

with both arms up in a

‘particle-friendly’ long vac-

loc or alpha cradle device.

Chin is up, with head rotated

away from the treated side.

Bilateral breast/chestwall

patients are treated on the

gantry, and the chin must

also be extended. There is

no head rotation for these

patients.

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Inclined Beam setup

Patient is positioned with both

arms down, and the ipsilateral

arm slightly akimbo.

Depending on the patient’s

anatomy, a wedge may be

inserted under the ipsilateral

side to achieve ‘enface’

position of the

breast/chestwall

Patient’s chin is also up, and

head turned away from the

affected side.

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Other views of the IBL setup

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Additional step in IBL Simulation Procedure

• Before pouring chemicals into the alpha cradle, a quick scan

must be done through the breast tissue to determine the angle of

the breast will be enface with the 30 degree gantry angle. A

reproducible, enface breast position needs to be achieved for the

treatment in the IBL.

• If the breast/cw angle is less than 30 degrees a small Styrofoam

wedge will be needed. This will be placed under the patient’s

affected chest wall area to turn the patient so that the

breast/chestwall is on a 30 degree angle.

• If the breast angle is more than 30 degrees the patient may need

to have the hips rolled toward the affected side to decrease the

angle.

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Patient Marks

• Once the breast box has hardened, start making the

treatment marks on the patient and box.

• Start with head position first: use the laser and have it

intersect the patient’s lips. Once this is done use a

marker and draw a line on the box to match; label as

lip line. If an arm is up mark on the patient’s elbow/

tricep area.

• Find the SSN and set sagittal laser to boney anatomy.

Try to make sure the SSN and end of sternum match

with the laser.

• Mark a three point set up on patient and box; about at

the end of the rib cage.

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Demonstration of patient marks

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CT Scan Specifications

• Scan from top of head to below inframammary fold.

• 1.25 mm slice thickness

• 65 FOV used to get entire treatment device in scan (necessary for

checking for device collisions and to make sure a beam isn’t

going through the device)

• Cradle will need to be offset in bore to have all of affected side in

scan. Indexing bar with offset is utilized.

• No 4D scan is necessary if magnitude of motion is less than

5mm. Breathing motion being in same direction as beam path.

First patients were done with 4D, but has been discontinued, as it

has been demonstrated to no longer be a concern and we want to

minimize excess dose for the patient.

• MD places wires for clinical borders and on scar.

The Treatment Planning

Process

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Fusion

• Fusions required:

– Not usually, unless patient is on BRE-008 protocol. Then

fusion with CT Angiography study is require for cardiac

vessel delineation.

– If patient was previously treated, then a deformable fusion is

done between the two treatment planning CTs. The

patient’s previous electronic DICOM radiation dose files are

requested for help with dose summation.

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MD Contours

• MD will contour the CTV_50.4, which is comprised of the

ipsilateral supraclavicular nodes, chestwall/breast tissue, axillary

lymph nodes, and internal mammary lymph nodes.

• RTOG guidelines for breast/chestwall and nodes are utilized, with

the exception that the entire ribs and chestwall are not included.

These areas were included in RTOG guidelines for simplicity, and

were not used to define regions of disease involvement, paths of

disease spread, nor regions at risk of reoccurrence.

• If patient is on the BRE008 study, the MD will also contour the

RCA, LAD 1st diagonal branch, and the LAD 2nd diagonal branch.

• If the patient is to have a tumor bed or scar boost, the MD will

draw these structures as well.

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Chestwall CTV and Coronary Artery contours

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Chestwall CTV on a Multi-Planar View

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Dosimetrist Contours

• R & L Lungs, plus Total Lung structure

• Heart

• Thyroid

• Esophagus

• Ipsilateral Brachial Plexus

• Skin

• Ipsilateral Humeral Head

• Patient External, including treatment devices

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Planning Techniques Utilized

• Regardless of which treatment room is used, a

matching fields, 3D forward-planned, uniform

scanning proton treatment plan is utilized.

– 2 fields used for the supraclavicular and superior axillary

node region

– 2 fields used for the breast/chestwall region

Gantry IBL

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Planning Techniques Utilized

• Why 4 beams per day????

– Robustness!

• Minimizes risk from daily setup error

• Allows for more homogeneous dose distribution,

minimizing hot/cold spots at the junction

• Spreads the surface dose between the 2 beams per

section, in order to spare the skin full dose from one

beam entry point.

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Beam Selection Criteria – Gantry Room

• Gantry Technique

– Want to utilize beams that are angled slightly off enface

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Gantry plan treatment angles

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Beam Selection Criteria - IBL

• Beam options are limited, therefore we position the

patient to make the angles optimal, having the beams

enter the patient as enface as possible.

– 1 set of Left or Right anterior oblique matching fields at

G30T0

– 1 set of Anterior Superior Oblique matching fields at

G30T270

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Beam Selection Criteria - IBL

LAO

beams

ASO

Beams

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Beam Selection Criteria - IBL

Demonstration

of 1 set of the

ASO matching

fields to cover

the entire CTV.

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IBL plan treatment angles

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Planning Techniques Utilized

• In both techniques, all 4 fields are treated per day,

incorporating 2 matchlines between the

supraclavicular and chestwall/breast regions.

• Fields are matched at depth using a dosimetric, not

geometric match line.

• Junction selection, isocenter placement, and air gaps

tightened as much as possible are crucial for these

types of plans.

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Isocenter Placement and Snout Size Restrictions

• Largest snout size 25 cm

• The CTV extends from the most superior

supraclavicular node to inferiorly just below the

implant or 2 cm below the former inframammary fold.

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Isocenter Placement and Snout Size Restrictions

• In order to make the most efficient treatment possible,

isocenters are selected so that both the superior and

inferior volumes share the same X and Z coordinates,

and only an inferior Y shift is necessary on a daily

basis.

• It is also crucial to select an X position so that the

breast/chestwall region is centered in the snout, and

that there is room to add adequate aperture margin.

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Isocenter Placement and Snout Size Restrictions

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Junction Selection

• Crucial to achieving an optimal treatment plan with

well-behaved compensators.

• Select junction in region where the supraclavicular

nodes end and the chestwall volume begins.

• Want to keep deep portion of nodal volume separate

from breast/chestwall region.

• Drastic changes in depth within a compensator can

cause hot spots and steep ridges.

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Junction Selection

• Since there are 4 total fields treated daily, two sets of

fields are matching, and the junctions are about 1 cm

apart.

Matchline 1

Matchline 2

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Optimized Air Gaps

• It is important in proton therapy to keep as tight of an

air gap between the end of the compensator and the

patient’s skin as much as possible.

• Tighter air gaps = sharper lateral penumbra

• Sharper lateral penumbra = matchlines that are easier

to optimize!

• However, this is not always achievable, due to the size

of the chestwall/breast volume, and the ability to fit it

in the snout.

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Optimized Air Gaps

• Take away: keep it as tight as possible, but make sure

your PTV will fit into the snout with adequate margin

for lateral coverage

Air Gap = 10 cm Air Gap = 25 cm

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Plan Optimization

• Once all beams are added, isocenters are set, air gaps

are finalized, and the junction areas are determined,

then:

– Apertures are added to all beams, and optimized so 95% of

the PTV is covered laterally

– Compensators are added, and tapered to remove any ridges

greater than 2 cm

– Ranges and modulations are set to cover the CTV by the

100% ISL. Dose coverage specifications are that the D95%

of the CTV must equal 100% of the Rx, and the D99% must

equal 95% of the Rx.

– Matchlines are tweaked so that the hot/cold areas are equal

in size

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Plan Optimization

• Each beam is optimized so that the CTV coverage

constraint is met

• Then, uncertainties are added to the range and

modulation for each beam

– Our center uses 2.5% + 2 mm for the CT HU to stopping

power conversion uncertainty and cyclotron delivery

precision uncertainty

• Organs at risk are now evaluated

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Target Dose Constraints

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Organs at Risk Dose Constraints

Dosimetric Advantages of

Protons

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In Isodose Distributions

Proton Doses

Photon Doses

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In Isodose Distributions

Proton Doses

Photon/E-

doses

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In Isodose Distributions

Proton Doses

Photon/E- Doses

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In Isodose Distributions

Proton Doses

Photon/E- Doses

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In the Dose Volume Histograms

Proton

Plan

Photon/

E- Plan

Photon/E- Plan

Lt Breast

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In the Dose Volume Histograms

Proton

Plan

Photon/

E- Plan

Rt Breast

Proton Plan

Photon/E- Plan

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In the Dose Volume Histograms

Proton

Plan

Photon/

E- Plan

Lt Breast

Proton Plan

Photon/E- Plan

The Treatment Delivery

Process

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Patient Alignment

• Alignment Process

– Align patient’s mouth with superior marks on cradle

– Line up both superior and inferior patient marks with vac-loc/alphacradle marks

– Align 3 point tattoos

– Align anterior tattoo with SSN and Navel for straightening

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Daily Setup Fields

• Once the patient is aligned, the first setup field is

imaged. This is done to make sure that the arm,

head/chin, and humeral head are in the right position.

At this point any directional shifts may be applied for

the set up field.

• The setup fields are typically at 0 or 90 degree gantry

angles.

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Daily Setup Fields

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Treatment Order – Gantry Room

• After filming at site setup, both supraclavicular fields

are treated first.

• Then, an isoshift, generally just in the Y direction

inferiorly, is performed.

• Finally, after filming post shift, both chestwall fields

are treated.

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Treatment Order – Inclined Beam Room

• Start with Supraclavicular field with Table 0 Gantry 30,

shift inferior

• Then, treat the breast/chest wall field at Table 0 Gantry

30.

• Swing couch, and treat breast/chest wall field at Table

270 Gantry 30. Then, shift superior.

• Finally, treat the supraclavicular field with Table 270

Gantry 30

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Daily IGRT Shift tolerances

• Tolerances:

– Site Setup/Supraclavicular field:

• anatomy within 2mm in X, Y, & Z

• Allow 1 Degree pitch, roll, & rotation

– Matching Chestwall field

• Anatomy within 4mm in X & Z

• No Y, pitch, roll, or rotation, in order to maintain the

geometry for the match

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Treatment Times, Setup Films taken

• Avg.tx.time table time thus far=49.5 min

• Avg.# of setup x-rays= 3.1

• Total #breast patients treated to with these techniques

to date: 18

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Conclusions

• Will continue to offer proton therapy to these

subgroups of breast cancer patients, as the organ

sparing benefits have convinced us that this is a

worthwhile option for these patients.

• Continue to look for ways to make the entire planning

process more efficient.

• Other indications:

– Partial Breast treatment for early stage – treated 1 patient

per protocol thus far

– Pencil Beam Scanning on the Gantry for the Stage III and

retreat patients

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References

• PCG BRE-008 Cardiac-Sparing Post-Mastecomy Protocol

• Ares, et al, Postoperative Proton Radiotherapy for Localized and

Locoregional Breast Cancer: Potential for Clinically Relevant

Improvements, Int. J. Radiation Oncology Biol. Phys. 76, No. 3,

pp. 685–697(2010)

• Fagundes, et al, Abstract poster presentation at PTCOG 2013

• H. Paganetti: Range ncertainties in proton therapy and the impact

of Monte Carlo simulations, Phys. Med. Biol 57 R99-R107 (2012)

• RTOG Breast Cancer Atlas for Radiation Therapy Planning:

Consensus Definitions

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Acknowledgements

• Entire Physics and Dosimetry teams at ProCure

Chicago and Cadence Health.

• The Breast Team: Rachel Sewell, RT(T), Dawn Smith,

RT(T), Megan Marshall, RT(T), Jennifer Mitchell, RT(T),

Stephanie Hufnal, RT(T) Minu Vachachira, RT(T),

Lauren Curran, RT(T), Hilary Deeke RT(T), Lindsey

Havron, RT(T)

Thank you for your attention!!!