Optical Dosimeters: Basics and beyond

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Recent advances in non gel tissue equivalent
dosimeters Kevin Jordan DOSGEL 2008
Hersonissos, Crete, Greece
Schulich School of Medicine Dentistry
The University of Western Ontario
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Introduction

• Papers selected mostly from PubMed
  searches(2006-current, dosimetry, tissue
  equivalence,)
• Subset of dosimeters covered in talk
  I. optically stimulated luminescence
  II. Radiochromic film (EBT)

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Optical Dosimeters Part 1 optically stimulated
luminescence
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Optical Dosimeters Part 1 OSL
NanoDot
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Dosimetry Issues

• Measure ionizing radiation dose easily and
  inexpensively
• Detector must be robust, e.g., no fading, no
  sensitivity to heat or chemical fumes
• Detector must be small
• Read-out should be quick and simple

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• Characterization of OSLDs for clinical dosimetric
  measurements
• P. Jursinic, Med. Phys. 34 (12) 4594-4604, Dec.
  2007

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Aluminum Oxide

• Al2O3C (sapphire) has been used for personnel
  dosimetry since 1996
• Can be read out in many ways
• It is the same material used in sandpaper
• robust and not sensitive to
• environmental factors

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OSL Basics
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Low energy traps
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OSL Signal Sequential readings
E 6MV D 100cGy 10 min in dark
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OSL Signal Sequential readings

• E 9 MeV
• D 60cGy
• 10 min in dark
• FS 10x10 cm2
• 2cm of buildup
• SSD 100 cm

Our data Sept 08 Note Microstar reader reads low
if NanoDot not in optimum position
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Optical Illumination
15 ? - 2 hrs
93 ? - 2 hrs
98 ? - 45 s
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Sensitivity
E 6MV D 100cGy 8 min wait
4 / 10Gy
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OSLD Dose Response 6MV
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Angle of Incidence
E 6MV D 50cGy 10x10 cm2
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Depth Dose 15 MV
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OSLD Sensitivity
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OLSD Sensitivity (Sept 08)
Irradiation Conditions 100 cm SSD, 10 x 10 cm2,
bolus dmax Delivered 50 cGy (using 9 MeV
calibration low/high dose file) Data represents
mean standard deviation (5 measurements per dot)
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Temperature Dependence
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microStar NanoDot

• Measures radiation exposure with OSL
• Only small portion of stored information is
  removed when dose read
• Sensitive over wide range 0.01 mGy to 100 Gy
• Dose does not fade
• Allows for incremental readings and accumulation
  of total dose over time

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Summary

• Dot can be read repeatedly, 0.05 signal
  decrease/ reading
• After transient signal decays the signal is
  stable within 2 for 2.5 days
• Also reported stable for up to 100 days
• OSLDs can be re-used once optically annealed
• Supra-linear response above 300 cGy
• No dependence on temperature
• Inexpensive
• High precision and accuracy in measuring dose

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Optical Dosimeters Part 2 radiochromic
GAFChromic EBT film
EBT( external beam therapy) film www.ispcorp.com
International Specialty Products Self developing
radiochromic film, (silver halide film processors
being retired from hospitals and replaced
with digital imaging) Radiochromic films second
strength is energy dependence similar to tissue
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Optical Dosimeters Part 2 radiochromic
GAFChromic EBT film
C G Soares 2006 Radiat Prot Dosim 120 100-106
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Optical Dosimeters Part 2 EBT film
C G Soares 2006 Radiat Prot Dosim 120 100-106
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Optical Dosimeters Part 2 EBT film
C G Soares 2006 Radiat Prot Dosim 120 100-106
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Optical Dosimeters Part 2 EBT film
S Devic et al 2007 Med Phys 34 112-118
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Optical Dosimeters Part 2 EBT film
S Devic et al 2007 Med Phys 34 112-118
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Optical Dosimeters Part 2 EBT film
S Devic et al 2007
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Optical Dosimeters Part 2 EBT film
S Devic et al 2007 Med Phys 34 112-118
Spectral analogies in optical CT laser
vs filtered LED Can optical CT scanners measure
EBT film?
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Optical Dosimeters Part 2 EBT film
Menegotti et al 2008 Med Phys 35 3078-84
scatter effect? 1D problem
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Optical Dosimeters Part 2 EBT film
Menegotti et al 2008 Med Phys 35 3078-84
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Optical Dosimeters Part 2 EBT film
Menegotti et al 2008 Med Phys 35 3078-84
Excellent commercial website
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Optical Dosimeters Part 2 EBT film
M Ranade et al 2008 Med Phys 35 473-79
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Optical Dosimeters Part 2 EBT film
M Ranade et al 2008 Med Phys 35 473-79
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Optical Dosimeters Part 2 EBT film
M Ranade et al 2008 Med Phys 35 473-79
EDR2 film measured higher doses in the low dose
regions wrt to Mapcheck and EBT film
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Optical Dosimeters Part 2 EBT film
T Chueng et al 2006 Med Phys 33 2912-14
more silver ? larger penumbra
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Optical Dosimeters Part 3water phantom for film
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Optical Dosimeters Part 3water phantom for film
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Optical Dosimeters Part 4 3D moving phantom
H. Nakayama et al, 2008 Med Phys 35 1643
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Optical Dosimeters Part 2 radiochromic
GAFChromic EBT film
Summary EBT film over responds lt200 keV Caution
required in reading film, reader specific for EBT
spectrum preferred Similar scatter problems to
optical CT readers A common optical CT / EBT
film reader would be convenient!