Download Nuclear Physics - a Blessing to Mankind

UI Physics Colloquium Sept. 14, 2009
Nuclear Physics – a Blessing to Mankind:
Recent Advances in Radiation Therapies
for Cancer
Ruprecht Machleidt
Department of Physics, University of Idaho
Outline
•
•
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Cancer facts
How does radiation therapy work?
Passage of radiation through matter
Differences between electron, photon and
proton/heavy ion radiations
• The Bragg peak and its use in cancer therapy
• Proton/heavy ion facilities
• Conclusions
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Cancer facts
• Cancer is the second largest killer.
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Cancer facts
• Cancer is the second largest killer.
• How to fight cancer: detect it (early!) and erase it.
• One way of detection: Imaging (CT, MRI, PET,
…)
• Erasing cancer:
Surgery, chemo (both are invasive),
Radiation (non-invasive, involved in 50% of
cancer treatments)
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How does radiation therapy work?
• Radiation causes ionization.
• Most ionization occurs on water (80% of our
body)
• Generates free radicals, e.g., OH*, chemically
extremely reactive.
• Radicals react with other molecules, disrupting
and disabling them, e.g., DNA.
• Cell with damaged DNA can continue to live,
but dies at next cell division.
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Healthy cells versus cancer cells
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Healthy cells versus cancer cells
under radiation
• Healthy cells are able to repair themselves.
• Cancer cells less able, and they divide more
often (recall: cell-death occurs upon cell
division).
• Thus, more damage is done to cancer cells.
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“Fractionation”
Example:
• Total dose: 80 Gray (Gy)
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Talking about units …
• The unit for absorbed dose is
1 Gray (Gy) = 1 Joule/kg = 100 rad
• 10-3 Gy/year is safe.
• 102 is lethal.
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“Fractionation”
Example:
• Total dose: 80 Gray (Gy)
• This is broken up into 40 portions: 2 Gy per
portion
• 5 portions per week (weekend free, healthy
cells can recover)
• Total radiation treatment: 8 weeks.
• Fractionation enhances the survival of the
healthy cells.
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Goal of all cancer therapies
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Do lethal damage to the cancer (tumor).
Do minimal damage to healthy tissue.
Not so easy!
What radiation is best suited to reach the
above goal?
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What radiations are there?
And what are the differences?
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Passage
of
radiation
through
matter:
Energy
deposition
Bragg Peak
Heavy
Ions
Photons
Electrons
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Differences in the energy depositions
• Electrons: small depth, “superficial”. The light
electrons bounce off heavy atoms: chaotic zigzag
path. The electrons are not getting anywhere.
• Photons: Exponential fall-off, like light passing
through milky/foggy glass.
• Protons and heavy ions: They have a mass;
so they stop after losing their kinetic energy.
Shortly before stopping, they do maximum
ionization: Bragg peak.
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How are photons absorbed?
Photon reaction mechanisms as a function of energy:
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Photon absorption by pair creation
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Passage Radiation
of Particles
Therapies
through Matter
Phys
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Medical applications in cancer
treatment
• Electrons: Skin cancer (“superficial”)
• Photons (X-ray): deeper lying tumors
• Protons and heavy ions: deeper lying tumors
What’s the difference between
photons and protons?
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PHOTONS
Tumor
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PHOTONS
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PROTONS
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PROTONS
more energy
Deeper lying
Tumor
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“Bragg Peak”
PROTONS
PHOTONS
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“Bragg Peak”
PROTONS
more energy
PHOTONS
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Reducing the disadvantage of photons:
“Multi-field”
But the same is done with protons and
then it’s even more effective.
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Some History
1905
W. H. Bragg and R. Kleeman, University of
Adelaide, discover the “Bragg Peak” using alpha
particles from radium; Phil. Mag. 10, 318 (1905).
1946
R. R. Wilson proposes medical use of protons;
Radiology 47, 487 (1946).
1954
First human treated at Berkeley.
1961
Harvard starts proton therapy (9000 patients
treated by 2003).
1988-90
2009
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First hospital-based proton accelerator
(synchrotron) built at Loma Linda University
Medical Center, S. California.
12,000-th proton patient treated at Loma Linda;
more than 55,000 patients treated world-wide.
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Loma Linda
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Comparing different treatment
protocols for prostate cancer
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The Proton Center at Loma Linda
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The proton beam treatment room (gantry) from the patients view
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In contrast: a photon treatment “center”
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The cost
• Proton facilities are expensive, but when run
efficiently [16 hours per day (two shifts), 64
patients per treatment room per day, 3
rooms: 192 patients per day], the cost per
patients gets within a factor of two to photon
(X-ray, “conventional”) radiation therapy.
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The cost: example
• Proton therapy: ≈$40,000
• Photon (X-ray, “conventional”): ≈$20,000
• BUT: you have to add the follow-up cost. With
large side effects, there are large follow-up
costs. $5,000 follow-up costs per year (for a
photon case with severe side effects) generates
costs of $50,000 in 10 years, $100,000 in 20
years, …
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Some useful links
• www.protons.com
• www.proton-therapy.org
• www.protonbob.com
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Conclusions
• Nuclear physics saves lives every day.
• Radiation treatment using beams of heavy charged particles (protons,
ions) allows to focus on localized tumors due to the Bragg peak, thus,
dramatically reducing negative side effects.
• It is the preferred method for the removal of tumors that are difficult
to reach by surgery (scull base, back of the eye) or where surgery has
typically large side effects (prostate cancer).
• Proton therapy has been used for 50 years and is well tested with longterm (10y) follow-up studies. It is not experimental.
• Medicare and most (but not all!) health insurances pay nowadays for
proton therapy.
• However your doctor may have never heard about proton therapy or
thinks that it is something very weird and untested.
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