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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


• 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


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


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


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


Profile of proton beam – PBP

Beam

25 mm collimator PMMA plates TLD foil

Experimental setup Pristine Bragg Peak


Profile of proton beam – SOBP

Beam

25 mm collimatorPMMA plates TLD foilSOBP

wheel

Spread Out Bragg PeakExperimental setup


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


MCP-2D relative efficiency – η

TL response depends not only on dose but also on ionization density.


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


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)


Thank You for Your attention
