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

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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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