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Medical Physics / Volume 37 / Issue 6 / RADIATION THERAPY PHYSICS

Med. Phys. 37, 2445 (2010); http://dx.doi.org/10.1118/1.3327455 (12 pages)

Treatment plans optimization for contrast-enhanced synchrotron stereotactic radiotherapy

M. Edouard

INSERM, U836, Equipe 6, B.P. 170, Grenoble Cedex 9 F-38042, France; Université Joseph Fourier, B.P. 51, Grenoble Cedex 9 F-38041, France; and European Synchrotron Radiation Facility, B.P. 220, Grenoble Cedex 9 F-38043, France

D. Broggio

Institut de Radioprotection et de Sûreté Nucléaire, Laboratoire d’Evaluation de la Dose Interne, IRSN/DRPH/SDI/LEDI, B.P. 17, Fontenay-aux-Roses Cedex F-92262, France

Y. Prezado

European Synchrotron Radiation Facility, B.P. 220, Grenoble Cedex 9 F-38043, France

F. Estève, H. Elleaume, and J. F. Adam

INSERM, U836, Equipe 6, B.P. 170, Grenoble Cedex 9 F-38042, France; Université Joseph Fourier, B.P. 51, Grenoble Cedex 9 F-38041, France; European Synchrotron Radiation Facility, B.P. 220, Grenoble Cedex 9 F-38043, France; and Centre Hospitalier Universitaire, B.P. 217, Grenoble Cedex 9 F-38043, France

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(Received 17 September 2009; accepted 30 January 2010; revised 28 January 2010; published online 6 May 2010)

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Purpose: Synchrotron stereotactic radiotherapy (SSRT) is a treatment that involves the targeting of high-Z elements into tumors followed by stereotactic irradiation with monochromatic x-rays from a synchrotron source, tuned at an optimal energy. The irradiation geometry, as well as the secondary particles generated at a higher yield by the medium energy x-rays on the high-Z atoms (characteristic x-rays, photoelectrons, and Auger electrons), produces a localized dose enhancement in the tumor. Iodine-enhanced SSRT with systemic injections of iodinated contrast agents has been successfully developed in the past six years in the team, and is currently being transferred to clinical trials. The purpose of this work is to study the impact on the SSRT treatment of the contrast agent type, the beam quality, the irradiation geometry, and the beam weighting for defining an optimized SSRT treatment plan.
Methods: Theoretical dosimetry was performed using the MCNPX particle transport code. The simulated geometry was an idealized phantom representing a human head. A virtual target was positioned in the central part of the phantom or off-centered by 4 cm. The authors investigated the dosimetric characteristics of SSRT for various contrast agents: Iodine, gadolinium, and gold; and for different beam qualities: Monochromatic x-ray beams from a synchrotron source (30–120 keV), polychromatic x-ray beams from an x-ray tube (80, 120, and 180 kVp), and a 6 MV x-ray beam from a linear accelerator. Three irradiation geometries were studied: One arc or three noncoplanar arcs dynamic arc therapy, and an irradiation with a finite number of beams. The resulting dose enhancements, beam profiles, and histograms dose volumes were compared for iodine-enhanced SSRT. An attempt to optimize the irradiation scheme by weighing the finite x-ray beams was performed. Finally, the optimization was studied on patient specific 3D CT data after contrast agent infusion.
Results: It was demonstrated in this study that an 80 keV beam energy was a good compromise for treating human brain tumors with iodine-enhanced SSRT, resulting in a still high dose enhancement factor (about 2) and a superior bone sparing in comparison with lower energy x-rays. This beam could easily be produced at the European Synchrotron Radiation Facility medical beamline. Moreover, there was a significant diminution of dose delivered to the bone when using monochromatic x-rays rather than polychromatic x-rays from a conventional tube. The data showed that iodine SSRT exhibits a superior sparing of brain healthy tissue in comparison to high energy treatment. The beam weighting optimization significantly improved the treatment plans for off-centered tumors, when compared to nonweighted irradiations.
Conclusions: This study demonstrated the feasibility of realistic clinical plans for low energy monochromatic x-rays contrast-enhanced radiotherapy, suitable for the first clinical trials on brain metastasis with a homogeneous iodine uptake.

© 2010 American Association of Physicists in Medicine

ACKNOWLEDGMENTS

The authors would like to thank Professor Franck Verhaegen for providing the spectra data, ESRF SCISOFT team, especially Rainer Wilcke and Dr. Claudio Ferrero for MCNPX and other software issues, and Mathias Vautrin and Pierre Deman for DICOM segmentation.

Article Outline

  1. INTRODUCTION
  2. MATERIAL AND METHODS
    1. Monte Carlo simulations: Source code
    2. Monte Carlo simulations: Geometries and irradiation parameters
      1. Human head analytical phantom
      2. Brain tumor, patient specific data
  3. RESULTS
    1. Dose enhancement in the tumor
    2. Dose distribution versus beam quality
    3. Dose distributions according to irradiation geometry
      1. Axial DVHs
      2. Volumetric DVHs
    4. Use of margins for increasing dose distribution homogeneity
      1. Dose homogeneity versus tumor position
    5. Optimization of dose distribution by weighting the beams
      1. Analytical human head phantom
      2. Patient specific data
  4. DISCUSSION
    1. Contrast agent enhanced radiotherapy using synchrotron radiation
      1. Contrast agent type and concentration
      2. Optimal irradiation energy
    2. Dose distribution optimization
  5. CONCLUSION: TOWARD A TREATMENT PLANNING SYSTEM THAT CAN BE USED IN CONTRAST-ENHANCED CLINICAL TRIALS
Digital Object Identifier
http://dx.doi.org/10.1118/1.3327455

KEYWORDS and PACS

Keywords

biological effects of X-rays, computerised tomography, dosimetry, phantoms, physiological models, radiation therapy, tumours, X-ray applications, stereotactic radiotherapy, synchrotron radiation, Monte Carlo dosimetry, contrast agents

PACS

PUBLICATION DATA

ISSN

0094-2405 (print)  

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physicists in Medicine

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