The role of gelatin in a methacrylic acid based gel dosimeter

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The role of gelatin in a methacrylic acid based
gel dosimeter

• DOSGEL2008
• Sep. 29th Oct. 3rd, 2008
• Hersonissos, Crete, Greece

S.HAYASHI, M.YOSHIOKA, S.USUI, K.HANEDA and
T.TOMINAGA Dept. clinical radiology, Hiroshima
Int. Univ. , JAPAN
Japanese green tea
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Motivation

• MAGAT type gel dosimeter Gelatin
  affects the polymerization of monomers.
  No response in R2 is observed in a sample without
  gelatin after irradiation.

• Does polymer form in a solution without
  gelatin ? or not?

• Polymerization is exothermic reaction.

• Temperature monitoring of sample during
  irradiation.

• The dependency on gelatin concentration in
  the temperature variation.

• Gelatin was replaced by a few amino acids and
  the other acids.

• The another role of gelatin in MAGAT type
  dosimeter.

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Gel composition
I. MAGAT Type
The gel was poured into glass vials (4 cm
diameter and 7 cm height).
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Method (1/3) Irradiation

• Facility Medical linear accelerator
• ( MITSUBISHI Co. EXL-12SP )
• at Hiroshima Int. Univ. (Japan)
• Beam 6 MV photon
• Dose 5, 10 and 20 Gy
• Dose rate 2 Gy/min
• SSD 100 cm
• Field size 40 x 40 cm2
• Room temperature 23oC

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Method (2/3) Temperature measurement

• Test phantom 60 ml vial bound by PE sheet
• Thermometer Digital, accuracy of 0.3 oC
• Time Irradiation start to 3600 sec.

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Method (3/3) MR Imaging

• Whole body MRI scanner
• ( 0.3T AIRIS II Comfort, Hitachi Medical Co.)
• at Hiroshima
  Int. Univ. (Japan)
• multiple spin-echo
• TR 4000 ms, TE1 20ms, TE 2100ms
• transverse relaxation rate
• S signal intensity at TE

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Result (1/4)Dose-R2 responseswith gel
containing different concentrations of gelatin
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Result (2/4)Temperature variations due to
irradiation
Gelatin conc. is 40 g/L
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Result (3/4)Gelatin conc. vs. Max temperature
variation
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The another role of gelatin ?
Gelatin initiates the polymerization.
What causes the polymerization ? Particular
region (amino acid residue) of gelatin ? Higher
order structure (such as helix) of gelatin ?

• Gelatin was replaced by Glycine
  (H2N-CH2-COOH), Alanine (H2N-CHCH3-COOH),
  Proline (HN(CH2) 3CH-COOH), Acetic acid
  (H-CH2-COOH), Propionic acid (H-CHCH3-COOH).

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Result (4/4)Temperature variations due to
irradiationin amino acid solution
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Summary Future plans
Thank you!

• Gelatin is an indispensable component for
  polymerization in MAGAT type gel.
• Gelatin might be use as trigger to initiate
  polymerization.

Application to the gel dosimeter with new
component. (by M.Yoshioka et al. in this
conference.)

• Gelatin can be replaced by an amino acid.
• The temperature rising after irradiation
  (overshoot).

Possibilities Creation of gelatin radicals to
initiate the polymerization. Grafting of
monomers onto gelatin (radicals?) and propagation.
Clarification of the mechanism of the
polymerization for development of new convenient
gel dosimeter.
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Responses
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Result in opacity
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Similar structures
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Gly conc. R2
0 and 20 Gy
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Method (3/3) MR Imaging

• Whole body MRI scanner
• ( 0.3T AIRIS II Confort, Hitachi Medical Co.)
• multiple spin-echo
• TR 4000 ms, TE1 20ms, TE 2100ms
• transverse relaxation rate
• S signal
  intensity at TE
• Estimation of opacity
• by the mean pixel value of digital picture

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An application
Polymerization cant occur in gelatin free
solution. Polymerization can occur even by a
small amount of gelatin.
Gelatin might be use as trigger to initiate
polymerization, not matrix, in a gel dosimeter.
Application to the gel dosimeter with new
component. (by M.Yoshioka et al. in this
conference.)