Einfhrung in die Physikalischen Grundlagen der Magnetresonanz MR Akademie fr den radiologisch techni

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Center for Medical Physics and Biomedical
Engineering
PAG and normoxic MAGAT gels
Dose response for electrons and photons
Aspects of radiation beam quality and their
effect on the dose response of polymer gels
photons, electrons and fast neutrons
fieldsAndreas Berg, Christian Bayreder, Dietmar
Georg, Achim Bankamp, Gerd Wolber
Fast neutron fields
Dose efficiency e for neutrons
A. Berg, DOSGEL 2008, HernissonsGreece
29.09.-03.10.2008
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History energy dependance
A. R. Farajollahi et al. The British J. of
Radiology 72, 1085-1092 (1999).
BANG polymer gels D 5 Gy
BANG-polymer gels (gelatin 5, acrylamide, 4
BIS 4) - no significant energy dependence in
dose response at D 5 Gy
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History Energy Dependance
Novotny et al. Medical Physics, 28, 2379-2386
2001

• BANG-2 polymer gels
• no significant energy dependence in dose
  sensitivity
• trend reduction in dose response for higher
  energies

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History energy dependance
Y. De Deene et al. The fundamental radiation
properties of normoxic polymer gel dosimeters a
comparison between a methacrylic acid based gel
and acrylamide based gels, Phys. Med. Biol. 51,
653673 (2006).
nPAG (acrylic acid polymer gels with THPC)
E1 6 MV E2 25 MV

• nPAG (acrylic acid polymer gels with THPC)
• no significant energy dependence in dose
  response for photons

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History energy dependance HIGH-LET
Gustavsson H, Bäck S, Medin J et al., Phys. Med.
Biol. 49, 3847-55 (2004)
A. Berg et el. Biomedizinische Technik/Biomedical
Engineering 50 S1 118-119 (2005)

• MAGAT- polymer gels methacrylic acid THPC
• significant reduction in dose response in high
  LET region

S Dgel/Dreference lt 1
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History energy dependance High LET
Ramm et al, Phys. Med. Biol. 45 N95-102 (2000)
BANGTM polymer gels

• BANGTM polymer gels
• significant LET dependence in dose response

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AIMS Energy dependence of polymer gel response
1.) MAGAT Methacrylic Acid Gel and
THPC photons E 100 keV to E 15
MeV electrons E 4, 12, 20 MeV 2.) PAG
(BANG) Polyacrylamide and Nitrogen
Flushing neutrons ltEgt 7 MeV
Linear accelerator Vienna/Austria
cyclotron DKFZ Heidelberg/Germany
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METHOD and MATERIALS Polymer Gels
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MATERIALS Polymer Gel Composition

• 1.) Gelatin
• to 700 ml water (T 25C)
• after swelling heating to 50C (1/2h) -gt clear
  solution
• cooling down to about 35C.

2.) methacrylic acid solution (50g50g) (100 ml)
3.) THPC solution (70 ml)
Mixture by continuous stirring.

• Containers
• 30 ml vials
• (outer diameter 28 mm)
• BAREX? (BP Amoco, UK)

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RESULTS Dose Response for Photons and Electrons
C. Bayreder, PHD-thesis Med. Univ. Vienna 2008
Polymer gel type MAGAT-gel

• Dose response for several beam qualities
  (MAGAT-Gel)
• seemingly trend to higher sensitivity at
  low-energy photons especially in high dose
  region
• Caution dose rates are different !

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Results dose response for photons and electrons
C. Bayreder PHD-thesis Med. Univ. Vienna 2008
Polymer gel type MAGAT-gel

• Dose response by sensitivity (DR2/DD) for several
  beam qualities
• left x-ray and photons 0,3 lt E lt 15 MV
  right e-beams 4 lt E lt 20 MeV
• No significant difference (with consideration of
  high dose rate for photons and electrons)

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Results dose response for photons and electrons
C. Bayreder PHD-thesis, Med. Univ. Vienna 2008

• Dose response for several dose rates as typical
  for clinical linear accelerators
• Left Dose response at low dose (2 Gy)
  Right Dose response at high Dose (5Gy)
• Significant reduction of dose response in high
  dose range (Dlt5 Gy)

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Results dose response for photons and electrons
C. Bayreder PHD-thesis, Med. Univ. Vienna 2008

• Dose sensitivity for several dose rates as
  typical for clinical linear accelerators
• reduced sensitivity as indicated by DR2/DD
• interpretation model diffusion time of
  monomers for finding polimerization partners is
  reduced til recombination with other radical
  carrying partners takes place -gt lower
  polimerization level

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Neutron-Irradiation

• Source compact cyclotron (Scanditronix MC 32
  NI) DKFZ/Heidelberg/Germany
• protons on thick Be-target p(16,7 MeV) Be -gt
  n
• fast neutron field
• (13x13 cm2), ltEgt _at_ 7 MeV

• position polymer gels 3,3 cm to surface
• - cylindric water container (d20cm, h13 cm)
• - rotation of the container with polymer gels
• (homogeneous irradiation)
• reference dosimetry (calibration of MU)
• - boron-ionization chamber
• calibrated in small volume ref. ionization
  chamber
• (Vol. 0,6 cm3, PTW Freiburg, Deutschland)

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Photon - Irradiation

• Co60
• E1 1.17 MeV, E2 1.33 MeV
• low LET, Q 1
• Dose range
• D 2, 4, 8, 12, 16 Gy
• Position samples
• water container PMMA (d5 mm)
• depth 1.5 cm
• Reference dosimetry
• ionization chamber

Irradiation arrangement at Co60-Gammatron Siemens
(DKFz, Heidelberg/Germany)
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RESULTS Dose response in a fast neutron-field
A. Berg et al. MR-basierte Polymergel-Dosimetrie
Neutronen- und Photonen-Antwort Tagungsband (ISBN
3-925218-77-7) 34. Jahrestagung DGMP (2003)
e (DR2/DDn0)/(DR2/DDCo60) 0,37 lt 1
Neutron field ltEgt _at_ 7 MeV

• Dose response of PAG-Gel within a fast neutron-
  and a Co-60 photonfield
• significat reduction in dose response dose
  efficiency lt 1

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DISCUSSION Dose Response in a fast Neutron-Field
Interpretation Model Fast neutron-field (ltEgt _at_
7 MeV) energy dissipation mainly scattered by
Hydrogen (p) (p-contribution to KERMA 90 of
KERMAall) -gt lower energy protons -gt high-linear
energy transfer (LET) -gt low mean free path
between radical molecules in irrradiation
direction -gt recombination of radical carrying
monomers and other molecules with radicals -gt
reduction in dose response
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CONCLUSION AND SUMMARY

• Dose response of MAGAT gels
• in photon and electron fields
• - independent on energy (0,1 MeV lt E lt 20 MeV)
• taking into account dose rate dependence
  within accuracy of measurement
• dependent on dose rate in middle and especially
  high dose region near saturation region
• Dose response of PAG-gels in Co60- and fast
  neutron fields (ltEgt _at_ 7 MeV)
• Significant reduction in dose response,
  efficiency e 0,37 lt 1
• most likely due to high LET of backscattered
  protons

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RESULTS 3D-data set surface projection
A. Berg ICMP 14.09.2005

• 3D-dose distribution of Dose image as obtained
  from a T2-map in the polymer gel
• Voxel size 250 x 250 x1000 µm3
• Mtx 128 x 128 x 20
• number of single point measurements for a
  zero-dimensional dosimetric method (ionisation
  chamber, diode etc.)
• 330 000 measurements!

5 mm
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ACKNOWLEDGEMENTS

• Mayor of Vienna
• (Hochschuljubiläumsstiftung der Stadt Wien, Nr.
  H-194-99)
• Austrian National Bank
• (Österreichische Nationalbank ÖNB Projekt
  Nr.10229/2003)

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Center for Medical Physics and Biomedical
Engineering
PAG and normoxic MAGAT gels
Dose response for electrons and photons
Aspects of radiation beam quality and their
effect on the dose response of polymer gels
photons, electrons and fast neutrons
fieldsAndreas Berg, Christian Bayreder, Dietmar
Georg, Achim Bankamp, Gerd Wolber
Fast neutron fields
Dose efficiency e for neutrons
A. Berg, DOSGEL 2008, HernissonsGreece
29.09.-03.10.2008