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 CaSO4Zeff 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)

DiodeTLD

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 + CaSO4: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:DyMCP-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

Thank You for Your attention

Jan Gajewski IFJ PAN / DKFZ

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