novel system for 2d dose map s in complex radiotherapy treatment verification

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Novel system for 2D dose maps in complex radiotherapy treatment

verification

Maria Cristina Battaglia3rd oPAC Topical Workshop on Beam Diagnostics, CIVIDEC, Vienna, 8th-9th May 2014

http://ec.europa.eu/research/mariecurieactions/



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Outline

Motivation The RADIA project Detector characteristics Characterization of the system (setup and

data analysis) Algorithm for 2D dose map reconstruction

(setup, theory and tests) Conclusions and perspectives Bibliography

3rd oPAC Topical Workshop on Beam Diagnostics, CIVIDEC, Vienna, 8th-9th May 2014


MotivationRadiotherapy plays an important role in the treatment of a wide range of

cancers

Very important: monitoring the dose delivered to the patient

A novel dosimetric system based on silicon detector for radiotherapy treatment verification.

Advantages: silicon detectors have good radiation hardness; on line treatment verification -> for example, no need of film development; acceptable spatial resolution; reproducibility; dose maps in the axial plane.

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The RADIA project: 2D dosimetric method for radiotherapy treatment verification using silicon

detectors


TWO DETECTORS

A feasibility study:W1 SS 500

A commercial Single Sided Silicon Strip Detector (SSSSD)

New detector based on BB7 technology

Dual chip SSSSD, designed by our group,

following clinical constraints

Patent at OEMP (Oficinal Española de Patentes y Marcas), Ministry of Industry & Commerce:

Number P201101009 (13/09/2011)


Detectors characteristics


Characterization of the system: experimental set up (1)

Mechanical systemBOX SLAB PHANTOM

Siemens Linac in 6 MV photon mode

Irradiation tests performed at the Virgen

Macarena Hospital in Seville

Detector placed perpendicularly to the beam


Characterization of the detector (2)Complete characterization of the system in terms of:

(a) linearity:The response of each strip is linear as function of irradiation time



(b) uniformity:a fundamental step to establish a common ground behavior for the strips of each detector



(c) Percentage Depth Dose (PDD): study of the dose at different depth in solid water, compared to the ionization chamber data



(d) Penumbra: penumbra is defined as the region located between 20% and 80 % of the maximum dose level along X and Y directions

Detector irradiated by asymmetric fields


Algorithm for dose map reconstruction (setup)

Cylindrical phantom: new project

Housing the detector

• Versatile and rotating phantom;• homogeneus: water equivalent

material;• Able to house different detectors

(films, ionization chambers, strip detectors,..)

Detector parallel to the beam fieldDose maps in the axial plane

Old system setup


Algorithm for dose map reconstruction: radon transform

Mathematical algorithm for dose map reconstruction based on:

Radon Transform

𝑅 {𝑓 (𝑥 , 𝑦 )}=𝑔 (𝑥 ′ ,𝜗 )=∫−∞

+∞

𝑓 ¿¿

: our set of data for each angle θ

f(x,y): the function representing the dose map we want to reconstructTo solve the equation: back projection theorem


Algorithm for dose map reconstruction: back projection

𝑓 (𝑥 , 𝑦 )=∫0

𝜋

𝑔 (𝑥 ′ ,𝜗 )∗𝐹 −1 ¿¿

Real case with the detector Discretization is needed

The dose in each pixel is reconstructed by the formula:

,(,Where:• a is the strip lenght, • n is the number of strips, • q is the number of measurements,• Δθ is the angular step between consecutive measurements.

Filter


Dual chip SSSSD: 32 strips for both detectors

Algorithm for dose map reconstruction: tests

SSSSD: 16 strips (developed by M.A. Cortés Giraldo, University of Seville)

Simulated dose map image of a circle (R=9 mm) for both the systems

Reconstructed area 48x48 mm2 64x64 mm2

Image resolution 3 mm 2 mmAngular range 0º-180º 0º-90ºAngular step 5º 3º


Conclusions and perspectives

• The new detection system shows good performances in radiotherapy conditions;

• A preliminary, complete characterization of the system as a dosimeter has been done;

• New set of measurements, with the new cylindrical phantom;

• Calibration of the system in such configuration;

• Implementation of new algorithm for dose map reconstruction

Work to be done :


Appreciated contributions to make this project a success have been received from the silicon detector manufacturer, Micron Semiconductor Ltd., web:

www.micronsemiconductor.co.uk (Dr Susanne Walsh Design /Colin D.Wilburn Director), ATI Sistemas S. L., www.atisistemas.com (Mrs. Marta Trueba) and

Instalaciones Inabensa.

Acknowledgment

Radia Collaboration

Department of Atomic, Molecular and Nuclear Physics, University of Seville: GETERUS group (M. A. Cortés Giraldo, M. I. Gallardo, J. M. Quesada), J. M. Espino (also CNA), M. C. Ovejero and A. Selva.

University Hospital “Virgen Macarena”, Seville (SAS): R. Arráns, H. Miras.

National Accelerator Centre (CNA): Z. Abou-Haïdar, M. Alvarez, M. C. Battaglia, A. Bocci.

Department of Electronic Engineering, University of Seville: A. Pérez Vega-Leal


Bibliography

(1) A. Bocci, M. A. Cortés-Giraldo, M. I. Gallardo, J. M. Espino, R. Arráns, M. A. G. Alvarez, Z. Abou-Haïdar, J. M. Quesada, A. Pérez Vega-Leal, and F. J. Pérez Nieto, “Silicon strip detector for a novel 2D dosimetric method for radiotherapy treatment verification”,

Nucl. Instrum. Methods Phys. Res., Sect. A. 673, 98 (2012).(2) Z. Abou-Haïdar, A.Bocci, M. A. G. Alvarez, J.M. Espino, M.I. Gallardo, M.A. Cortés-Giraldo, M.C. Ovejero, J.M. Quesada, R. Arráns, M. Ruiz Prieto, A. Pérez Vega-Leal y F.J. Pérez Nieto. “Output factor determination for dose measurements in axial and perpendicular planes using a silicon strip detector”, Phys. Rev. ST Accel. Beams 15,042802 (2012).(3) M.A.Cortés-Giraldo, M.I. Gallardo, R. Arráns, J.M. Quesada, A. Bocci, J.M. Espino, Z. Abou-Haïdar and M. A. G. Alvarez, "Geant4 simulation to study the sensitivity of a Micron silicon strip detector irradiated by a Siemens PRIMUS linac", Progress in Nuclear Science and Technology, Vol. 2, pp. 191-196 (2011).(4) Patent at the OEMP - Oficina Española de Patentes y Marcas – Ministry of Industry & Commerce: Number P201101009 (13/09/2011).


Thank you

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novel system for 2d dose map s in complex radiotherapy treatment verification

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