a (quick) survey of (some) medical accelerators dr. todd satogata brookhaven national laboratory...
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A (Quick) Survey of (Some)Medical Accelerators
A (Quick) Survey of (Some)Medical Accelerators
Dr. Todd SatogataBrookhaven National Laboratory
SUNY Stony Brook PHY 684 – September 5, 2007
The NASA Space Radiation Laboratory at BNL X-Rays for imaging and cancer therapy Dose advantage for hadron cancer therapy Cyclotrons vs synchrotrons in hadron therapy PET imaging
September 5, 2007 T. Satogata - PHY 684 2
The NASA Space Radiation LaboratoryThe NASA Space Radiation Laboratory
Long-range space travelers (e.g. to Mars) are exposed to high radiation doses
Most concern is about heavy ions from galactic cosmic rays, solar wind
Less expensive to simulate/study on earth
Biological effects of high radiation doses of this type are controversial DNA damage, repair Mutagenesis Carcinogenesis Cellular necrosis
p-Fe, 200-1000 MeV/u
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X-Ray ImagingX-Ray Imaging
By far the most common use of medical radiation X-ray tubes: 1-2% efficiency Typical energies from 10-100
keV X-rays made by
brehmsstrahlung Follows dose attenuation curve Image shadow of X-rays
stopped
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X-Ray Cancer TherapyX-Ray Cancer Therapy
Conventional X-ray cancer treatment accelerators are “small” Nearly all of it visible here 5-25 MeV X-rays
x100 diagnostic X-ray Generated by a small
linacA few MV/m (Linac lecture 9/19)
500+ US locations
Treatment planning and beam shaping are challenging on patient-by-patient basis
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X-Rays vs ProtonsX-Rays vs Protons
Most proton dose is deposited in the sharp"Bragg Peak", with no dose beyond
X-rays deposit most of their dosenear the surface (skin) of the patient
Scanning the proton energy makes aSpread Out Bragg Peak (SOBP) that spansthe depth of the tumor
Carbon and other light hadrons also work –but beware of nuclear dissociation
100-250 MeV protonspenetrate 7-37 cm
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X-Rays vs Protons IIX-Rays vs Protons II
Photons/X-rays do not stop at a well-defined boundary Dose conformity is much better with protons than X-
rays
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X-Rays vs Protons IIIX-Rays vs Protons III
With multiple angles/fields, protons excel even better The “spine” is better protected Dose to surrounding (healthy) tissues is intrinsically lower
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Cancer Therapy AcceleratorsCancer Therapy Accelerators
X-rays, protons, and light ion beams are all used in modern cancer radiotherapy
Need to minimize side-effects Minimize dose to healthy tissue But dose cancer enough (~5
krem) X-rays are:
less expensive (>500 US locations) better for peripheral/surface
tumors Protons/Ions are:
more expensive (~5 US locations) better for deeper, critical tumors
CAT, MRI, PET imaging all came from accelerator technology
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Two Existing US Proton Therapy FacilitiesTwo Existing US Proton Therapy Facilities
Loma Linda (California)
- synchrotron source
- built/commissioned at Fermilab
- world leading patient throughput
Mass General Hospital (Boston)
- cyclotron source (IBA)
- 1st patient Nov 2001
- coming up to speed
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Cyclotron vs Synchrotron: CyclotronCyclotron vs Synchrotron: Cyclotron
Fixed energy output at constant current
Energy degrader reduces beam energy
Collimators scrape beam to size
Large intrinsic beam size in all three dimensions
(ACCEL superconducting cyclotron for RPTC, Munich)
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Cyclotron vs Synchrotron: SynchrotronCyclotron vs Synchrotron: Synchrotron
Accelerate variable beam intensity to variable energy 50-250 MeV No energy degrader Smaller beam sizes
Accelerate either Small beam
intensity rapidly (30-60 Hz), extract in one turn
Large beam intensity slowly, extract in many turns
(Rapid Cycling Medical Synchrotron, RCMS)
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Cyclotron vs Synchrotron: TableCyclotron vs Synchrotron: Table
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The Rapid Cycling Medical SynchrotronThe Rapid Cycling Medical Synchrotron
Synchrotron
Treatment Room
Treatment Room
Tumor Scanning
Bragg Peak
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Dielectric Wall AcceleratorsDielectric Wall Accelerators
A recent new development in hadron therapy accelerators Alternating fast-switching
transmission lines – gradients up to 100 MV/m (!!)
Requires advanced materials Very high-gradient insulators High-frequency/voltage switches
In development by LLNL and Tomotherapy Group
10+ years from delivery
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PET ImagingPET Imaging
PET: Positron Emission Tomography Tag metabolically active
compounds with positron emitterse.g. 18F deoxyglucose
Emitted positrons annihilate with nearby electrons producing back to back 511 keV gamma rays
Coincident gamma rays detected with photomultiplier tubes or avalanche photodiodes
Metastasizedprostate cancer
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