Radiation protection issues in proton therapy

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Radiation protection issues in proton therapy
Protons
IMRT
Tony Lomax, Centre for Proton Radiotherapy,
Paul Scherrer
Institute, Switzerland
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• Overview of presentation
• Proton therapy An overview
• Radiation protection issues Staff
• 3. Radiation protection issues The patient
• 4. Summary

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Proton therapy An overview
Depth dose curves for photons (15MV) and protons
(177MeV)
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Proton therapy An overview
The Spread-Out-Bragg-Peak
target
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Proton therapy An overview
Passive scattering in practice
Range-shifter wheel
Scatterer
Target
Patient
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Proton therapy An overview
Active scanning
Proton pencil beam
Target
Patient
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Proton therapy An overview
Example actively scanned proton treatments
Meningioma (3 fields)
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• Overview of presentation
• Proton therapy An overview
• Radiation protection issues Staff
• 3. Radiation protection issues The patient
• 4. Summary

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Radiation protection issues Staff
A typical proton therapy facility (e.g. PSI)
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Radiation protection issues Staff
A typical proton therapy facility (e.g. PSI)
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Radiation protection issues Staff
Radiation protection issues for proton therapy

• Even the highest energy protons (250MeV) stop in
  a few centimeters of concrete
• So the main concern from the radiation
  protection point of view are not protons but
  secondary particles, in particular neutrons.

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Radiation protection issues Staff
1/cm of primary protons are lost due to
interactions with atomic nuclei, which then
produce secondary particles. E.g.
Primary protons
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Radiation protection issues Staff
Secondary particle production by protons
E.g. MCNPX Monte Carlo calculations for a passive
scattering nozzle (Hitachi, Houston)
p and p flux
Fontenot et al, Phys. Med. Biol. 53 (2008)
16771688
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Radiation protection issues Staff
The PSI proton therapy facility and its major
neutron sources
OPTIS2 (Passive)
Gantry 2 (scanning)
Gantry 1 (scanning)
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Radiation protection issues Staff
Analytically calculated equivalent dose rates
(µSv/h)
OPTIS2 (Passive)
0.3
0.05
2.0
1-2
Gantry 2 (scanning)
0.13
Gantry 1 (scanning)
0.03
0.02
Major sources of neutrons
Teichmann 2004, Internal PSI report
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Radiation protection issues Staff
Shielding for proton therapy facilities

• Based on analytical calculations (confirmed by
  measurements) dose rates in entrances, control
  rooms and public areas can be reduced below legal
  limits
• For the PSI facility, to reduce extraneous
  neutron dose minimum of 2-4 meters of concrete is
  required
• For a single treatment room, concrete costs
  alone can be of the order of 500000 pounds or
  more

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Radiation protection issues Staff
How accurate are analytical calculations?
Newhauser et al 2002, Nucl. Inst. Meth. Phys.
Res. 476, 80-84
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• Overview of presentation
• Proton therapy An overview
• Radiation protection issues Staff
• 3. Radiation protection issues The patient
• 4. Summary

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Radiation protection issues The patient
Neutron and photon scatter doses for protons and
photons
103
103
102
102
101
101
Neutron equivalent dose (H/mSv/Treatment Gy)
Absorbed dose (D/mGy/Treatment Gy)
100
100
10-1
10-1
Irradiated volume
10-2
10-2
10-3
10-3
0
40
20
60
80
Distance from target (cm)
Adapted from Haelg et al 2012, Submitted to
Medical Physics
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Radiation protection issues The patient
but dont forget the primary dose
A comparison of non-target integral doses for
IMRT and scanned protons for nine pediatric cases
IMRT
Protons
On average, protons reduced integral dose by a
factor 2
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Radiation protection issues The patient
Are there potential cost consequences from
reducing integral dose?
With thanks to Hakan Nystrom, Skandion Clinic,
Sweden
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Radiation protection issues The patient
Are there potential cost consequences from
reducing integral dose?
Effective dose (protons) 4000mSv / 2
2000mSv
Alpha value saving 2000mSv x 100 200000 per
patient!
With thanks to Hakan Nystrom, Skandion clinic,
Sweden
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Summary

• Due to the Bragg peak characteristics of the
  depth dose curve, proton therapy can deliver
  highly conformal treatments with significantly
  reduced integral dose to the patient.
• Due to the limited range of therapeutic protons
  (lt32 cm in water), challenges for radiation
  protection and shielding are mainly to do with
  secondary neutron production
• Analytical shielding calculations are relatively
  straightforward but tend to overestimate
  transmitted dose rates. MC calculations are more
  accurate . Consequences for shielding costs?
• The significantly reduced integral dose of
  protons may have important radiation protection
  (and cost? ) consequences for the patient,
  particularly pediatrics.

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Thank you!