Sam Ju Cho

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Sam Ju Cho
A Study on the characteristic of normoxic polymer
gel dosimeter according to its composition

• Dept. of Radiation Oncology
• Dongguk University International Hospital

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Introduction
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Introduction
To evaluate complex radiation therapy such as
IMRT, IGRT, SRS and brachytherapy, The polymer
gel has been developed as a 3D dose verification
dosimeter Need for the polymer gel to use as a
dosimeter Have to know the dose response
characteristic for different dosimetry
requirement Because the polymer gel is a type of
chemical dosimeter Component type and
composition ratio of polymer gel affect the dose
response characteristic
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Introduction
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Materials and Methods
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Materials and Methods
Ø 1.6 cm, W 6 cm
Normoxic polymer gel fabrication and test vial
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Materials and Methods
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Materials and Methods
30x30x30 cm3 water phantom Medical linac 6 MV
Put the test vials in the 2 dose uniformity of
water phantom TRS 398 protocol for dose
calibration
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Materials and Methods
MR image acquisition
Before imaging, put the test vials in the MR room
(24 h) Styrofoam case for the test vials 1.5T
and Head coil Multi spin-echo, MX 256, ST 5 mm,
FOV 180, BW, 130, NEX 1 TR 3000 ms, TE 30 240
ms equal space
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Materials and Methods
Dose response delivered dose D and measured MR
T2 (1/R)time
relationship Dose sensitivity dose response
divide by delivered
dose D Dose reproducibility deviation of
T2 variation among
measured gel dosimter - 8 gelatin, 8 MAA,
10 mM THPC, 0.05 mM HQ - 2, 4 Gy to each 5 vials
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Materials and Methods
Dosimeter analysis

• Dose accuracy delivered dose Dd and measured
  dose
• Dm relationship
• - 8 gelatin, 8 MAA, 10 mM THPC, 0.05 mM HQ
• 0, 2, 4, 6 Gy delivered to each 3 vials for
  fitting curve
• using fitting curve, Absorbed doses were
  calculated
• for 10 vials which used dose reproducibility
  study
• Dose rate dependency dose rate and measured dose
  D
• relationship
• - 8 gelatin, 8 MAA, 10 mM THPC, 0.05 mM HQ
• 200 MU/min, 600 MU/min and 2, 6 Gy delivered

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Materials and Methods
Dose uncertainty used as measurement dose error
Combined standard uncertainty of the dose
For a 95 level of confidence
Dose resolution for a given level of
confidence, the minimal detectable dose
For a 95 level of confidence
Baldock C, Lepage M, Bäck SÅJ, et al. Dose
resolution in radiotherapy polymer gel dosimetry
effect of echo spacing in MRI pulse sequence.
Phys Med Biol 46449-4602001
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Results
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Results
T2 time calculation I
T2 times of each polymer gel were calculated by
using TR, TE and signal intensity
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Results
T2 time calculation II
Signal intensity versus TE
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Results
Dose response I
The concentration of the gelatin is high, the
threshold R2 value increase and the dose response
decreases.
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Results
Dose response II
The concentration of the MAA is high, the
threshold R2 value decrease and also the dose
response decrease.
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Results
Dose Sensitivity I
The concentration of the gelatin increase, the
dose sensitivity increase within some rage.
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Results
Dose Sensitivity II
The concentration of the MAA increase, the dose
sensitivity increase within some rage.
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Results
Dosimetric Characteristic I
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Results
The solid line is a calibration curve and the
circles are measured data for dose accuracy
evaluation
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Results
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Results
Dose rate dependency is shown in the high dose
region of high dose rate
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Conclusions
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Conclusions
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Thank you for your attention