Determination of Angular dependency of OSLDs with respect to 6 Megavolt photon radiation using Linear Accelerators

1. Presenter: SUBHRENDU GHOSH
Fortis Memorial Research Institute
Gurugram , Haryana
Determination of Angular Characteristics of
Optically Stimulated Luminescence Dosimeter
Subhrendu Ghosh, Radhakrishnan B Nair, Kanan Jassal, Tarun Kumar, Vinoth
Kumar, Elan Mariagandhi, Ashu Abhishek, Amal Roy Chaudhoory

2. CONTENTS
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Introduction
Background and Motivation
Method
Results
Comparison
References

3. Introduction
Optically Stimulated Luminescence
Dosimeter (OSLD) is a passive dosimeter like
TLD.
Multi read-out is possible.
Lesser time consuming.
The material mainly used is Al2O3:C .
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4. Introduction(cont.)
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5. Motivation
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The response of an OSL detector
depends on the following factors :
Mass
Errors that may arise during
measurement by the reader.
How many times the OSLDs are used .
Geometrical Factors

6. Geometrical Factor
The most important factor out of all the mentioned factors .
The OSL crystals are placed in a rectangular cassette .
As it is composed of thin layer of crystals, the angle of
incidence of beam plays a major role .
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7. Materials used
PMMA slabs comprising a total thickness of 12 cm.
Microstar OSLDs (Nanomet technology)
ELEKTA SYNERGY LINAC.
0.6 cc farmer chamber with Electrometer( PTW unidos)
OSL Reader (Landauer,Inc/Microstar)
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8. Method
Verification of the set-up and
reliability of OSLD reading:
 0.6 cc farmer chamber was
placed in the appropriate slot at
5 cm depth from surface.
 150 MU was delivered to the
chamber centre with 6 MV
photon beam with 100 cm SSD
with 10 x10 cm2 FS
 From the 6 MV PDD data, the
surface dose was derived as
44.86 cGy.
 Dose measured with OSLD was
45.78 cGy.
 The variation was 2% validating
the set up and the reliability of
OSLD dose. 8
.

9. Method
• A total of 37 OSLDs were
calibrated and selected for the
study
• Graph paper was pasted over
slab to ensure positional
reproducibility.
• The crosswire of the OSLD was
matched with LINAC crosswire.
 150 MU was delivered by 6 MV
photon beam with 100 cm SSD
and 10 x 10 cm2 FS at zero
degree gantry angle.
• Gantry angle was incremented
at the rate of 100 from +900 to -
900 and 150MU was delivered at
each angle by changing the
OSLD 9

10. Method
• The first set of OSLDs
were deployed with
orientation in G-T
direction
• The second set of
OSLDs were deployed
with orientation
perpendicular to G-T
direction
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A--B
C--D
GUNTOTARGET
C--D
A--B
GUNTOTARGET

11. Results
OSLD response at various
gantry angles along G-T
OSLD response at various gantry
angles perpendicular to G-T
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12. Results(cont.)
Along G-T direction Perpendicular to G-T direction
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13. Results(cont.)
The above graphs display the dependence of
OSLDs on the incident beam angle
It was observed that as the beam incident angle
increases, the measured surface dose
increases.
It was also observed that the surface dose
increases at slower rate up to 500 beam angle
and thereafter increases steeply.
 The dose values measured in two orientations
agree within 1% to 2% for almost all the angles of
incidence.
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14. Fasihah Hanum Yusof’s Study
Angular dependence of
OSLD was earlier studied
by Fasihah Hanum
Yusof, etal
• Plots obtained from our
study follow the similar
pattern of this study
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15. Comparison
Fasihah Hanum Yusof’s
measurement
The measurements were
done from -750 to +750 at
150 increments
The measurements were
not done in two different
orientations
11 data points
Our measurement
Measurements had a wide
range from +900 to -900 with
100 increments
Measurements were done in
two different orientations
perpendicular to each other
37 data points in two
orientations put together
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16. Future Scope
The mathematical formulation of the trend seen in the graph
can be derived.
The Physics behind the different response at different gantry
angles.
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17. Conclusion
The dose responses by the OSLDs at various angles of
incidence were studied for 6 MV photon beam and it was
observed that:
Dose responses increase with increase in angle of
incidence, at a slower rate up to 500 on either side and
steeply up to 900.
The responses were almost similar irrespective of the
orientation of the OSLDs in perpendicular or along the G-T
direction
The angular dependence needs to be considered while
deploying the OSLDs for in-vivo dosimetry or surface dose
estimation applications
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18. References
 Fasihah Hanum Yusof, Ngie Min Ung. On the Use of Optically Stimulated
Luminescent Dosimeter for Surface Dose Measurement during
Radiotherapy. PLoS One v.10(6); 2015.
 Jursinic PA, Yahnke CJ. In vivo dosimetry with optically stimulated
luminescent dosimeters, OSLDs, compared to diodes; the effects of
buildup cap thickness and fabrication material. Medical physics.
2011;38(10):5432–40.
 Lehmann J, Dunn L, Lye JE. Angular dependence of the response of the
nanoDot OSLD system for measurements at depth in clinical
megavoltage beams. Med Phys. 2014 Jun;41(6):061712.
 Joerg Lehmann , Leon Dunn. Angular dependence of the response of the
nanoDot OSLD system for measurements at depth in clinical
megavoltage beams. Med Phys. 2014 May.
 Jursinic PA. Changes in optically stimulated luminescent dosimeter
(OSLD) dosimetric characteristics with accumulated dose . Med Phys.
2010 Jan;37(1):132-40.
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19. 19
Comparison
• More data points were obtained in the current measurement and
hence a more genuine trend is achieved.
• Both the lateral sides were examined.