Transcript 2007-09-05-LectureNotes-Todd

A (Quick) Survey of (Some)
Medical Accelerators
Dr. Todd Satogata
Brookhaven 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
The 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
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DNA damage, repair
Mutagenesis
Carcinogenesis
Cellular necrosis
 p-Fe, 200-1000 MeV/u
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X-Ray Imaging
 By far the most common use of
medical radiation
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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 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 linac
 A few MV/m
 (Linac lecture 9/19)
 500+ US locations
 Treatment planning and
beam shaping are
challenging on patient-bypatient basis
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X-Rays vs Protons
X-rays deposit most of their dose
near the surface (skin) of the patient
Most proton dose is deposited in the sharp
"Bragg Peak", with no dose beyond
100-250 MeV protons
penetrate 7-37 cm
Scanning the proton energy makes a
Spread Out Bragg Peak (SOBP) that spans
the depth of the tumor
Carbon and other light hadrons also work –
but beware of nuclear dissociation
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X-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 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 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 Facilities
Loma Linda (California)
Mass General Hospital (Boston)
- synchrotron source
- cyclotron source (IBA)
- built/commissioned at Fermilab
- world leading patient throughput
- 1st patient Nov 2001
- coming up to speed
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Cyclotron vs Synchrotron: Cyclotron
(ACCEL superconducting cyclotron for RPTC, Munich)
 Fixed energy
output at constant
current
 Energy degrader
reduces beam
energy
 Collimators scrape
beam to size
 Large intrinsic
beam size in all
three dimensions
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Cyclotron vs Synchrotron: Synchrotron
(Rapid Cycling Medical Synchrotron, RCMS)
 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
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Cyclotron vs Synchrotron: Table
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The Rapid Cycling Medical Synchrotron
Bragg Peak
Treatment
Room
Treatment
Room
Tumor Scanning
Synchrotron
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Dielectric 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 Imaging
 PET: Positron Emission Tomography
 Tag metabolically active compounds
with positron emitters
 e.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
Metastasized
prostate cancer
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