New 3D radiochromic gel dosimeters with inhibited diffusion

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New 3D radiochromic gel dosimeters with inhibited
diffusion
Jaroslav olc1,2 Václav Spevácek1
1Czech Technical University in Prague 2Czech
Metrology Institute
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Radiochromic gels

• Change of color during irradiation
• can be evaluated using optical methods
• Fricke-gel dosimeter with xylenol orange
• the only wide-spread used
• main disadvantage fast ferric ions diffusion

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New radiochromic gels

• The main goal of the research
• development of radiochromic gels with suppressed
  diffusion
• 2 types of gels developed
• A gel based on creation of a dye Turnbull blue
• A gel based on creation of insoluble mercurous
  chloride (Hg2Cl2)

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Gel based on Turnbull blue

• Turnbull blue
• insoluble blue dye, KFeIIFeIII(CN)6
• particles of Turnull blue fixed in a gel matrix
• product of radiation-induced reactions
• 1. radiation-induced reduction of ferric ions
  (Fe3) to ferrous ions (Fe2)
• 2. interaction of ferrous ions with potassium
  ferricyanide (K3Fe(CN)6)
• 3. creation of Turnbull blue

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Gel composition

• 3 versions are suggested due to background and
  light-sensitivity issues

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TB gel version 1

• Overview
• gelatin concentration as low as possible (it
  increases background)
• no extra acid needed (ferric chloride dissolved
  in acid)
• Basic properties
• easy to prepare
• higher background (0.6 cm-1)
• moderate ageing

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TB gel version 2

• Overview
• gelatin concentration as low as possible (it
  increases background)
• ferric ammonium citrate instead of ferric
  chloride
• Basic properties
• easy to prepare
• low background (0.17 cm-1)
• high light-sensitivity
• moderate ageing

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TB gel version 3

• Overview
• gelatin replaced by agarose
• lower concentration of ferric chloride due to
  agarose lumping
• added ferric ammonium citrate
• no extra acid needed (ferric chloride dissolved
  in acid)
• Basic properties
• slightly complicated preparation (higher agarose
  melting point)
• low background (0.14 cm-1)
• very slow ageing

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Absorption spectra

• Absorption maximum of Turnbull blue 690 nm

Left to right 0 Gy, 25 Gy, 100 Gy
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Dose response

• Gel version 3
• Linearity up to at least 400 Gy
• Sensitivity 5x10-3 Gy-1cm-1

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Ageing

• For a gel in version 3
• Fast if stored at light
• Very slow if stored in a dark place at 5C

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Diffusion rate

• Determined from feathering of sharp dose gradient
• Diffusion ratelt 4x10-3 mm2h-1at 24C

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Gel based on mercurous chloride

• Mercurous chloride
• insoluble white chemical, Hg2Cl2
• particles of Hg2Cl2 fixed in a gel matrix
• product of radiation-induced reactions
• 1. solution of mercuric chloride containing Hg2
• 2. radiation-induced reduction of Hg2 to
  mercurous ion (Hg)
• 3. creation of insoluble Hg2Cl2

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Gel composition

• pH sensitive
• ideal pH 3.6 adjusted by adding a solution of
  sodium hydroxide

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Absorption spectra

• Light dispersion
• An unirradiated gel bright, transparent
• Irradiated gel - cloudy

Left 30 Gy, right 0 Gy
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Dose response

• Linearity up to at least 30 Gy
• Sensitivity 3.8x10-2 Gy-1cm-1
• at 850 nm

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Other characteristics

• Light sensitivity
• low
• Ageing
• slow (in a dark place at 5C)
• Background
• low (0.15 cm-1 at 850 nm)
• Diffusion rate
• lt 2x10-4 mm2h-1 at 24C

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Disadvantages

• Promising dosimetric characteristics but
• Toxicity of mercury
• Complicated evaluation of dose patterns
• cone-beam optical CT with problems
• no response on MRI

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Conclusions

• New radiochromic gels were developed
• Inhibited diffusion
• A gel based on Turnbull blue
• Can be evaluated using optical CT
• Easy to prepare
• Lower sensitivity
• A gel based on mercurous chloride
• High sensitivity
• Problems with evaluation
• Toxicity

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Thank you for your attention!