Two-Dimensional Thermoluminescence Dosimetry
System for Proton Beam Quality Assurance
Jan GajewskiInstitute of Nuclear Physics, Kraków, PolandGerman Cancer Research Center, Heidelberg, Germany
Existing methods used in dosimetryJan Gajewski IFJ PAN / DKFZ
TL pellet
diamond
OSL
ionization chamber
semiconductor diode
Films
• Gafchromic
• Radiographic
TLD foils
matrix of ionisation chambers
strip and pixel semiconductor detectors
Fricke gel
3-D scintillators
TLD personal badge
1-dimensional 2-dimensional 3-dimensional
Strip semiconductor detector 3-D Scintillator
2D TLD for proton beam QA
Presentation plan
• Principle of operation
• 2D Thermoluminescence System
• TL Foils
• Readers
• Dosimetric properties
• 2D TL system for broad beam Quality Assurance
• TL foils and LET-painting technique
• Summary and plans for future
2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ
The principle of 2-D TL Dosimetry
Preparation of foil
Irradiation
Heating
Collection of emitted light
Data analysis
2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ
• Water resistance and flexibility
• Up to 20 x 20 cm2
• Reusability
• Resolution below 0.1 mm2
• Linearity of dose response: 0.05-20 Gy
Dosimetric system – TLD foils2D TLD for proton beam QA
MPC-2D CaSO4
Zeff 8.1 13.4
Two types of foils:
• LiF:Mg,Cu,P (MCP-2D)
• CaSO4:Dy
Jan Gajewski IFJ PAN / DKFZ
Laboratory Reader:
• detector size 50 x 50 mm2
• resolution 640 x 480 px2
• fully adjustable
Clinical Reader:
• detector size 200 x 200 mm2
• resolution 1024 x 1024 px2
• easy and safe to use
Laboratory reader
Clinical reader
Dosimetric system – hardware2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ
Dosimetric properties – uniformity
After corrections the uniformity of readouts is around 2%
20 cm
2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ
Dosimetric properties – dose responseLinearity Index was constant within ±5% measured with the Laboratory Reader.
For the Clinical Reader it is ±2%
Laboratory Reader
Clinical Reader
±2%
2D TLD for proton beam QA
f(D)Df(D)
f(D)D
f(D)D
Jan Gajewski IFJ PAN / DKFZ
Dosimetric properties – Reproducibility
Repeatability was found below 2%
More than 20 equivalent irradiations and readouts
For previous reader and software it was 5%
For radiochromic films it is 1-6%[1] McLaughlin et al. Methods Phys. Res. A 302[2] N. V. Klassen et al. Med. Phys. 24
2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ
Beam cross-section in PMMA phantom
Irradiations have been performed with 60 MeV proton beam at IFJ PAN in Kraków
(AIC-144 cyclotron)
Diode
TLD
2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ
Profile of proton beam – PBP
Beam
25 mm collimator PMMA plates TLD foil
Experimental setup Pristine Bragg Peak
2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ
Profile of proton beam – SOBP
Beam
25 mm collimatorPMMA plates TLD foilSOBP
wheel
Spread Out Bragg PeakExperimental setup
2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ
Profile of proton beam – summary
3D visualisation of a cross-section of a proton broad beam
• About 100 beam cross-sections have been measured
• Dose profiles of beam measured with TL foils and photodiode are comparable
• Measured flatness of dose profiles is in 5-12% range (for diode it is 2-3%)
• Penumbra is broader with deeper location in phantom (difficult to measure with diode)
• Experiments conducted at IFJ PAN in Kraków show that 2D TLD system is a good tool for proton beam Quality Assurance
2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ
MCP-2D relative efficiency – η
TL response depends not only on dose but also on ionization density.
2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ
LET-painting with TL foils
Difference in relative efficiency
Set of two foils: MCP-2D + CaSO
4:Dy
Energy response for CaSO4:Dy foils needs to be verified
Biological response depends on ionisation density. Determination of LET is very important for ion radiotherapy.
The idea
Beam
CaSO4:Dy
MCP-2D
2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ
Plans for future• Incoming experiments (HIT-Heidelberg)
– Energy response for 12C and p+ ions
– Tests of QA of scanning beam
– Calibration curve for dose/LET dosimetry
– Validation of the dose/LET response in clinical conditions
– Other TL foils properties: transparency, angular response, fading, etc.
• 2D TLD system will be used for QA of therapeutic scanning beam at Bronowice Cyclotron Center in Kraków (C-235 IBA cyclotron)
2D TLD for proton beam QAJan Gajewski IFJ PAN / DKFZ