6/24/17 1 Tom Depuydt, ir, PhD Head of Medical Physics Radiation Oncology department UZ Leuven and ParTICLe Proton Therapy Center KU Leuven Proton Therapy Technology in the Clinic Scientific Meeting BVS-ABR: “Proton therapy – From the Need to the Solution” June 23 rd 2017 From radiation physics to a clinical radiotherapy treatment modality depth dose • Protons loose kinetic energy gradually w hen travelling through matter, through multiple collisions with atomic electrons • The rate of energy loss or “ stopping power ” depends on the kinetic energy its elf • Multiple Coulomb interactions with atomic nuclei make protons scatter • Non-elastic collisions with atomic nuclei knocks out one or more protons, neutrons, or nucleon clusters Evolution of delivery techniques of the last 20 years “Dose sculpting hitting the target avoiding other tissues” Classic Radiotherapy Highly conformal Radiotherapy Proton vs. photontherapy tumor tumor Intensity-modulated photon radiotherapy Proton radiotherapy High therapeutic dose level Intermediate/low dose level No dose Organ at Risk Organ at Risk Photon Proton No dose “Proton beams have no exit dose” No dose
Transcript
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Tom Depuydt, ir, PhDHead of Medical Physics
Radiation Oncology department UZ Leuven
and ParTICLe Proton Therapy Center
KU Leuven
Proton Therapy Technology in the Clinic
Scientific Meeting BVS-ABR:
“Proton therapy – From the Need to the Solution”
June 23rd 2017
From radiation physics to a clinical radiotherapy treatment modality
depth
dose
• Protons loose kinetic energy gradually when travelling through matter, through multiple collisions with atomic electrons
• The rate of energy loss or “stopping power” depends on the kinetic energy itself
• Multiple Coulomb interactions with atomic nuclei make protons scatter
• Non-elastic collisions with atomic nucleiknocks out one or more protons, neutrons, or nucleon clusters
Evolution of delivery techniques of the last 20 years
“Dose sculpting hitting the target avoiding other tissues”
• Technology to manage uncertainties in proton therapyo Image guidanceo Range verification (In-vivo)o Dual-energy CT for Stopping Power Estimationo Organ motion management/compensation
• Proton therapy facilities anno 2017o “Embedded” facilitieso Technology maturity
Layout of a “typical” PT facility
Fixed beam room
Cyclo vault
Rotating gantry room
Proton beam extracted from cyclotron
depth
dose
Bragg peak
Entrance plateau
Pencil beam
250MeV or 30 cm range
“Cyclotron produces small single high-
energy proton beam of ≈250 MeV”
Few mm width
Small “pencil beam”
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Passive scattering energy/range modulation• Create from a Bragg peak single
energy proton beam a Spread Out Bragg Peak (SOBP) covering a
volume in depth
• SOBP is a weighted sum of Bragg
peaks
• Range modulator wheels rotate at
high frequencies and “scan” the
Bragg peak fast in depth to create a
SOBP
SOBP modulation
Passive scattering nozzle• Create from a 3 mm diameter s ingle
energy proton beam a wide beam with homogeneous intensity (s imilar to linac system for photons)
• Multiple scatterers in a cascade,
homogenous or constructed from a
combination of rings of high-Z and
low-Z materials to refocus as many
protons as possible into the field
aperture
Passive scattering nozzle
target
SOBP modulation = Cte
Aperture + compensator
• Patient-specific Apertures and range compensators are used to
shape the beam and distal edge depth of the SOBP to the target volume contours
Towards Pencil Beam Scanning …
SOBP modulation = Cte
Target
Limited extra dose
SOBP modulation
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Scanning magnets for Pencil Beam Scanning (PBS)
F = q(v×B)
F=mv2=qvB
(if v�B)
R
BENDING
Y
X
Energy selection system
E = modified,
thus proton range is changed
Layer/Energy switching
Time=1-2 seconds
-Cyclotron produces single energy (fe. 250 MeV)-”Degrader + Bending magnet + movable slit” to select lower proton beam energy
Degrader
Dos
e
Depth
Energy switching
Scanning
target volume
Proton beam visualized in liquid scintillator solution
Courtesy PSICourtesy PSI
Pencil beam scanning over target volumeMagnetic deflection scanning
• Technology to manage uncertainties in proton therapyo Image guidanceo Range verification (In-vivo)o Dual-energy CT for Stopping Power Estimationo Organ motion management/compensation
• Proton therapy facilities anno 2017o “Embedded” facilitieso Technology maturity
Range uncertainty issue in proton therapy
The Gare Montparnasse becam e
famous for the derailment on 22
October 1895 of the Granv ille–Par is
Express, whic h overr an the buffer
stop. The engine c areer ed acr oss
almost 30 metres (100 ft) of the
station concours e, crashed through
a 60-centimetre (2 ft) thick wal l, shot
across a terrace and sm ashed out of
the station, plummeting onto the
Place de Rennes 10 metres (33 ft)
below, where it stood on its nose.
Proton range and the train metaphor …
“Protons do stop but there is an uncertainty on where exactly”
Paganetti et al. Phys. Med. Biol. 2012 and Knopf et al. Phys. Med. Biol. 2013
Reducing uncertainties in proton therapy
“3% to 5% proton range uncertainty”
Range uncertainty issue in proton therapy
• ... due to anatomical changes
Paganetti et al. Phys. Med. Biol. 2012 and Knopf et al. Phys. Med. Biol. 2013
• Technology to manage uncertainties in proton therapyo Image guidanceo Range verification (In-vivo)o Dual-energy CT for Stopping Power Estimationo Organ motion management/compensation
• Proton therapy facilities anno 2017o “Embedded” facilitieso Technology maturity
Image guidance in PT
• Historically indications treated with PT were close to bony structures
(cranial, spine, …) which were good natural fiducials for tomor location
• Planar X-ray imaging was the standard up to only a few years ago
Base of skull chordoma
Image guidance in PT
Difference in
particle track history
Range shift
“Example: Filling nasal cavities”
Image guidance in PT: Learning from XT !?
1999: David Jaffray and first CBCT integrated in XT linac
• Technology to manage uncertainties in proton therapyo Image guidanceo Range verification (In-vivo)o Dual-energy CT for Stopping Power Estimationo Organ motion management/compensation
• Proton therapy facilities anno 2017o “Embedded” facilitieso Technology maturity
Range verification in PT: Prompt gamma imaging
• Resulting from inelastic interactions of incident protons and target nuclei
• The nucleus is excited to a higher energy state and emits
a single photon (PG) as it returns to the ground state
• the isotropic PG rays can be detected instantaneously(within a few nanoseconds) following the nuclear
interactions
• Wide energy spectrum, between 0 and 7 MeV
• reasonably high production rate/signal for a typical
therapeutic dose of 2 Gy min−1
• PG are produced along the proton tracks, the path of a
pencil beam within the patient could be imaged as a line source by an adequate gamma camera.
• Real-time online verification method
Moteabbed et al. Phys Med Biol 2011
Slit-design gamma camera (IBA prototype)
Smeets et al. Phys Med Biol 2012
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Range verification in PT: Prompt gamma imaging
Smeets et al. Phys Med Biol 2012
Range verification in PT: Prompt gamma imaging
Slit cameraNozzle
Deviatio
n p
en
cil b
eam
ran
ge
Patient
Range verification in PT: In-vivo PET imaging
• Inelastic interaction of the proton beam with atomic nuclei create unstable isotopes
• Technology to manage uncertainties in proton therapyo Image guidanceo Range verification (In-vivo)o Dual-energy CT for Stopping Power Estimationo Organ motion management/compensation
• Proton therapy facilities anno 2017o “Embedded” facilitieso Technology maturity
Dual Energy CT imaging for Stopping Power Ratio estimation
• An estimation of Proton Stopping Power
Ratio’s (SPR) based on Single Energy CT
(SECT) has the issue that
materials/tissues with the same CT-number could have a different elementalcomposition, and SPR.
• Conversion of SECT into stopping powerresults in ~3-4% range uncertainty
• Dual energy computed tomography(DECT) can provide simultaneous
estimation of relative electron density ρe
and effective atomic number Zeff.
• Using the Bethe-Bloch formula SPR’s can
be estimated of different tissues based on a
DECT of the patient
Schneider et al. Phys Med Biol 1996
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Estimation of protonDual Energy CT imaging for Stopping Power Ratio estimation Dual Energy CT imaging for Stopping Power Ratio estimation
Dual-source CT (Siemens) Twinbeam (Siemens)
Au-filter Sn-filter
DECT Technology Overview
Dual Energy CT imaging for Stopping Power Ratio estimation Proton therapy technology in the clinic
• Technology to manage uncertainties in proton therapyo Image guidanceo Range verificationo Dual-energy CT for Stopping Power Estimationo Organ motion management/compensation
• Proton therapy facilities anno 2017o “Embedded” facilitieso Technology maturity
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Impact of organ motion on PBS dose delivery
0 1 2 3 4 5 6 7 8 9 100
0.5
1
1.5
2
2.5
Interplay effect between PBS scanned dose delivery and organ motion
Generating high dose region using
multiple pencil beams (spots)
“static” dose
0 1 2 3 4 5 6 7 8 9 100
0.5
1
1.5
2
2.5
Organ motion can change the position of the spots
relative to each other, resulting in hot/cold spots
Dose to a moving target
0 1 2 3 4 5 6 7 8 9 100
0.5
1
1.5
2
2.5
3
Rescanning N-times reduces the interplay effects
and approximately re-established the “static” dose
• Technology to manage uncertainties in proton therapyo Image guidanceo Range verification (In-vivo)o Dual-energy CT for Stopping Power Estimationo Organ motion management/compensation
• Proton therapy facilities anno 2017o “Embedded” facilitieso Technology maturity
History of Proton Therapy (PT) facilities
A by-product
“PT facilities evolves from being …”
EmbeddedModality
NUCLEAR
PHYSICS
RESEARCH
FACILITY
PT
Dedicated stand-alonefacility
PT
HOSPITAL
PT
PHYSICS/BIOLOGYRESEAR
CHFACILITY
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PT Facility size
60x100 meter
“The metaphors in PT …” “Size measure of PT centers … sport field?”
Range uncertainty
“Compact systems as enabling technology for embedding PT… ?”
15x28 meter
11x24 meter
PT Facility size
Impression of finished ParTICLe facility
UZ Leuven campus Gasthuisberg
PT EMBEDDED IN UZ LEUVEN
GASTHUISBERG CAMPUS
R
T
IBA S2C2 superconducting synchrocyclotron IBA Proteus ONE compact gantry beam-line
Scanning magnets
Energy selection
“Compact” PT systems
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ParTICLe Proton Therapy center in Leuven (Embedded)
• IAEA TRS-398 (2000), The current Code of Practice for proton dosimetry no PBS
• ICRU Report 78 (2007), coverage PBS limited
• IAEA: Update of TRS-398 (<2020?)
• AAPM TG-185: Commissioning of Proton Therapy Systems
• AAPM TG-224: Proton Machine QA
• NCS subcommittee on proton dosimetry
• EPTN ("ESTRO initiative")
• IPEM
“The current activity of different guideline working groups shows that PBS is getting to maturity, but it is not there yet. It also shows that existing guidelines do not meet the current needs.”
