Proton Beam Therapy at Mayo Clinic

Jon J. Kruse, Ph.D.Mayo Clinic Dept. of Radiation Oncology

Rochester, MN

History of Proton Therapy at Mayo

• 2002: Decided to consider particle therapy – analysis and education

• 2006: Initial meetings with manufacturers

• 2007: Initial RFP• Protons + Carbon• Scattered + Scanned beams

• 2008: Decision that the future was scanning particle beams

• 2/2010: Permission to Plan• RST + AZ

History of Proton Therapy at Mayo

• 3/2010: Final RFP, protons only

• 11/2010: Board of Trustees approval

• 12/2010: Selected Hitachi as vendor

• 5/2011: Mayo/Hitachi contract signed

• 9/2011: RST groundbreaking

• 6/2013: Equipment installation began

• 3/2015: First RST Tx rooms accepted

• 6/2015: First Tx in RST

Mayo Clinic Proton Beam Therapy Centers

• Two identical treatment facilities• Rochester, MN 2015• Phoenix, AZ 2016

• Synchrotron-based

• Four gantries (180 degrees)

• One fixed beam room

• All five nozzles in each facility are identical – optimized for scanning beam only

Mayo Clinic Proton Beam Therapy Centers

• Design goals• Highest quality treatment available• High efficiency

• ~1200 patients per year, per facility

• Infrastructure for efficient treatment of complex disease sites• Radiographic imaging suites outside

treatment room• Remote anesthesia• Scanning beam nozzles

Both Centers Adjacent to Photon Clinics

Facility Layout

Facility Layout

Half Gantry Treatment Room

10/15/2011

03/09/20125/8/2012

Richard O. Jacobson Building

05/03/20125/8/2012

Richard O. Jacobson Building

5/8/2012

Richard O. Jacobson Building05/22/2012

08/30/201210/08/2012

11/12/2012

Rochester Install 9-24-13

Rochester G3 9-24-13

Treating Cancer with Scattered Protons

Patient

Tumor

250 MeV Proton Beam

Patient

Tumor

250 MeV Proton Beam

Treating Cancer with Scattered Protons

Treating Cancer with Scattered Protons

Patient

Tumor

Reduced Energy Proton Beam

Treating Cancer with Scattered Protons

Patient

Tumor

Add Double Scatterer

Tradeoff between field size and range

Treating Cancer with Scattered Protons

Patient

Tumor

Add Field Aperture

Treating Cancer with Scattered Protons

Patient

Tumor

Custom machined brass part must be changed

between fields

Nozzle must be very close to patient

And brass is expensive, and a potential source

of neutrons

Treating Cancer with Scattered Protons

Patient

Tumor

Spread out peak with modulator wheel

Must accept maximum modulation width over

entire tumor

Treating Cancer with Scattered Protons

Patient

Tumor

Match Distal Proton Range with Compensator

Compensator must be machined for each field,

and changed by hand

250 MeV Proton Beam

Raster-scanned Proton BeamPatient

Tumor

Treating Cancer with Scanned ProtonsPatient

Tumor

Variable EnergyProton Beam

Y-Scanning Magnets

X-Scanning Magnets

Active Scanning Proton Beams

Passive Scattering Active Scanning

Proton Developments at Mayo

• Hitachi has installed a scanning proton treatment room at M.D. Anderson

•Mayo’s facility is scanning beam only

• Redesign of many components• Synchrotron• Gantry • Nozzle• Console/HMI• IGRT

• Efficient treatment of complex cases

MDA -> Mayo Synchrotron

Smaller Footprint24ft 18.5ft dia.

Fewer ComponentsLower CostLess PowerSimpler Maintenance

Fast Room SwitchSmaller Beam Spot

Gantry~5M smaller

~60 tons lighterBetter patient

access

Gantry~5M smaller

~60 tons lighterBetter patient

access

MDA

Mayo

Old Spot

New Spot

New Nozzle: Smaller Spot

10/08/2012 Richard O. Jacobson Building

TumorNormal Organ

Scanning Nozzle RedesignMD Anderson Nozzle Mayo Nozzle

Gillin et al., Med Phys 37 (2010) p. 154

New Console

New HMI

New HMI

HMI Design w/ RTT in Omika

~Monthly Design Meetings in Hitachi

Mayo-Hitachi Design Teams at Hitachi Works

Mayo-Hitachi Omika Teams at Omika Works

Facility Infrastructure for Complex Cases

Anesthesia SuiteImaging Rooms

Beam Matched Tx Rooms

Why Do Active Scanning?

• Dosimetric advantages• No tradeoff between field size/depth• Variable modulation width• Higher resolution distal range

compensation• No hardware in the beam

• Easier planning• IMPT• Adaptive planning without new hardware

• Efficiency• Cycle through Tx fields from control room

Why Not Do Active Scanning?

• Lateral penumbra• Scattered beams can achieve a very sharp

lateral penumbra, via brass aperture very close to the patient• With scanning beams, in some cases the

lateral penumbra is dominated by spot size in air – not as sharp as a collimated scattered beam

• Interplay• Time dependent dose delivery of a scanning

beam is problematic for moving tumors

Interplay• Scattered beams irradiate entire target

volume with almost no time dependence• Traditional photon ‘ITV’ approach to

moving targets works fairly well

• Scanning beams scan through the target volume• ~mSec time scale for a single spot• ~100s to 1000s spots per layer• ~Several to dozens of layers per field• ~Seconds to change energy• 1 field may take tens of seconds to ~ 1 min• Some portions of target may be double

painted, others missed

Interplay Effects

Bert et al., PMB 53 (2008) p. 2253

Solutions for Moving Targets

• Optimized Planning Parameters

• Gating

• Breath hold

• Repainting

• Tracking

Optimized Planning: Spot Spacing

Bert et al., IJROBP 73 (2009) p. 1270

Optimized Planning: Scanning Direction

Static 1 cm parallel 1 cm orthogonal

Johnson et al., in preparation

Delivery Options: Breath Hold

• Careful patient selection a must

• Feedback tools, coaching

• Reduced treatment time• Faster energy changes• Reduced number of energy levels

Reducing Number of Energy Levels

Gillin et al., Med Phys 37 (2010) p. 154

Reducing Number of Energy Levels

• Mini ridge filter introduces modest spatial dependence of beam energy

• Spatial component disappears quickly with phantom scatter

• Shallower dose falloff allows for fewer energy levels

• Decreased treatment time

• Higher dose/spotCournyea et al., AAPM 2013 Tues AM

Treatment Times with Ridge Filter

• Standard plans: • 67 s (no MRF)• <30 s (w/ MRF)

• Stereotactic plans:• 95.4 s (no MRF)• 47.7 s (min)

• Diminishing gains as MRF thickness increased. MRF Thickness (cm)

0 0.5 1 1.5 2 2.5

Ave

rage

Tim

e/F

ield

(s)

0

20

40

60

80

100 SRσ2

SRσ3 SRσ4

σ2

σ3 σ4

SRσ2

SRσ3 SRσ4

σ2

σ3 σ4

Cournyea et al., AAPM 2013 Tues AM

Delivery Options: Repainting

• Only a portion of the prescribed dose delivered in a single pass

• Repeat the delivery multiple times per fraction

• Individual hot/cold spots averaged out as number of repaints increases

Delivery Options: Repainting

1 Scan 10 Scans

Furukawa et al., Med Phys 37 (2010) p. 4874

IGRT in Mayo Clinic Half Gantry

• Fast Intra-Tx imaging at any gantry/couch position

• Fluoroscopy capable

• Large FOV

• No moving parts –stable imaging isocenter

• 6 DOF matching software

IGRT in Mayo Clinic Half Gantry

• Limited to two imaging angles

• FOV is 30 cm x 30 cm at isocenter –may not see center of tumor volume for non-isocentric plans

• Not CBCT capable

Utility of CBCT for Protons

• Bony anatomy is often a poor surrogate for target/critical anatomy

• Fiducials or CT localization required in cases where we expect movement of soft tissues relative to radiographically evident bony anatomy

• Photons: Place target tissue at isocenter, don’t worry about ‘upstream’ bony anatomy

• Protons: ??

CT Localization for Protons: Pelvis

• Change in position of bony anatomy alters dose distribution

• CT localization may be of limited use

• Change in position of rib causes minimal disturbance of dose distribution

• CT localization of lung tumors desirable for proton therapy

CT Localization for Protons: Lung

CBCT for Lung?

•Mayo proton facilities will be scanning beam only

• Treatments of mobile tumors will probably require gating/breath hold

• Free-Breathing CBCT imaging a poor reference for gated/breath held treatment

• Gated/breath held CBCT not impossible, but not easy

CBCT for Adaptive Protocols

• Proton dose calculation is extremely sensitive to CT number accuracy

• CT number accuracy / consistency not generally a priority in CBCT

• Increased scatter relative to helical CT degrades imaging performance

Helical/CBCT Phantom Images

Helical CT

CBCT

Images Courtesy of T.J. Whitaker

CT on Rails

CT on Rails

• Robot moves patient to imaging isocenter

• CT translates over patient for imaging

• Robot moves patient back to treatment isocenter while CT registration is performed

• Helical CT image quality• Images for adaptive imaging

• Fast image acquisition

• 4D imaging capability