01.11.2012

A manual Multileaf Collimator

for use in Cobalt-60 teletherapy

Gernot Echner, DKFZ Heidelberg

Stefan Ueltzhoeffer, Precisis AG

AMPICON 2012Mangalore, India

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G. EchnerDept. of Med. Phys. in RT

Introduction

• Recent reports: Need for affordable Radiotherapy in LMI1

• Quest for MLC for Co-60 machines

• Industrial partner for development: Precisis AG, Germany

IAEA, Radiation Oncology Physics Handbook, 2005

Rosenblatt et.al (IAEA), Radiotherapy&Oncology 104, (2012) 269-271

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G. EchnerDept. of Med. Phys. in RT

Background / Development constraints

• Adaptable to Co-60

• Up-to-date Dosimetry: <2% Leakage, Single Focus, Rounded Leafends (small

Penumbra)

• Field size 20x30 cm2

• Power source independent / Mechanical MLC

• Low Maintenance: Stable mechanism, Standard parts

• Low cost

Image: © Ideenkoch - Fotolia.com

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G. EchnerDept. of Med. Phys. in RT

Technical Solution (1)

Drive: Closed-loop Pneumatics

• Optimal “Spring” properties• High force• Low wearing

Leaf Material: Brass

Density = 8.47 g/cm3

μCuZn39Pb3 = 0.4311 cm-1 HVL = 1.6079 cm 6*HVL = 9.65 cm ≙ 1.563 %

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G. EchnerDept. of Med. Phys. in RT

Technical Solution (2)

• Drive integrated into Leaves (Compactness)

• Workflow: Mechanical field adjustment

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G. EchnerDept. of Med. Phys. in RT

Dosimetry: Material & Methods

Material• PTW Ion chamber• Theratron Elite80 (Ø1.5cm) & Theratronics Equinox (Ø2.0cm)

• GafChromic EBT film• PTW Phantom/Virtual Water

Methods• 80cm/85cm/100cm SSD• Varying field size • pdd & skin dose• Interleaf & End2End Leakage• Penumbra: 80% / 20%

Images: © Precisis AG

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G. EchnerDept. of Med. Phys. in RT

Dosimetry: Results Penumbra

Penumbra with depth Penumbra with fieldsize

Source Ø 2.0 cm:Reference Penumbra: 0.85 cm

Source Ø 1.5 cm:Reference Penumbra: 0.55 cm

Source Ø 2.0 cm, Depth 10 cmPenumbra: 0.69 cm – 1.39 cm

Pen

um

bra

/ cm P

enu

mb

ra /

cm

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G. EchnerDept. of Med. Phys. in RT

Dosimetry: Results Leakage

Interleaf Leakage End2End Gap

Average Leakage ~1.5%Max < 3%

End2End Gap ~5%Improved planned

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G. EchnerDept. of Med. Phys. in RT

Summary

Features:• Drive: Closed-loop Pneumatics, power independent• Field size: 20cm x 30cm• Leaf width: 10mm• Focus: Single focus + rounded leaf ends• Penumbra: < 10mm (Reference Field)• Leakage: < 2%• Compact design (65cm x 35cm x 12,5cm; 45kg)

Marketed by Precisis AG as „Cob(alt)Ra(diation)Leaf“

CobRaLeaf®

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G. EchnerDept. of Med. Phys. in RT

Outlook

• mark -> patient treatment

• Automatic Interlocking system

• Improve ergonomics (easier movement)

• Adaptation also to non-Theratronics machines

Image: © Anatoly Maslennikov - Fotolia.com

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G. EchnerDept. of Med. Phys. in RT

Acknowledgments

Martin Baumann1, Gernot Echner1, Armin Runz 1, Marco Langhans1, Roland Schwandtner2,

Dr. Jozef Kurzeja2, Prof. Irenaeus Admietz2, Mr. Stefan Ueltzhoeffer3, Andrei Ciresianu4, Mark Xu4,

Shawn Luimes4, Prof. Wolfgang Schlegel1

1Deutsches Krebsforschungszentrum, Heidelberg2Klinik f.Strahlentherapie, Evangelisches Krankenhaus Witten 3Precisis AG, Heidelberg4Best Theratronics, Ottawa, Canada

Thank you for your attention

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G. EchnerDept. of Med. Phys. in RT

Backup Information

Skin dose for 85 cm SSD

Field size Skin dose, 85 cm SSD Skin dose, 100 cm SSDEquinox Jaw size (cm)

5x5 54,70% 54,70% 6x6 10x10 59,90% 58,70% 12x12 20x20 79,50% 74,50% 25x25 20x30 79,40%

Properties Tungsten (Densimet®, Plansee)Density: 18.0 g/cm3 Minimum Attenuation w/o coherent scattering (cm2/g) for E=1.332 MeV: 0.0521 μW= 0.9378 cm-1

HVL = ln2/μ=0.739 cm 6*HVL ( Residual:1.563 %) = 4.43 cm (target) Residual: 2.0 % -> 5.644 HVL = 4.17 cm (minimum)

Maximum edge length

Tumor/PTV

10cm 20cm 30cm 40cm0.00%

20.00%

40.00%

60.00%

80.00%

100.00%Co-60

Linac_EN

Linac_DE

Gesamt

Maximum Edge length is >=

Cas

es

Fieldsize Study

Max. Edge length

=>Approx.80% of casestreatable in 1 field