Treatment plans optimization for contrast-enhanced synchrotron stereotactic radiotherapy

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 pa...

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Bibliographic Details
Published in:Medical physics (Lancaster) 2010-06, Vol.37 (6), p.2445-2456
Main Authors: Edouard, M., Broggio, D., Prezado, Y., Estève, F., Elleaume, H., Adam, J. F.
Format: Article
Language:English
Subjects:
Algorithms
biological effects of X‐rays
Brain
Brain Neoplasms
Brain Neoplasms - surgery
Cancer
Computer Simulation
computerised tomography
contrast agents
Dose‐volume analysis
dosimetry
Dosimetry/exposure assessment
Gold
Humans
Life Sciences
Models, Biological
Monte Carlo dosimetry
Monte Carlo methods
Neurons and Cognition
phantoms
Photons
physiological models
radiation therapy
Radiation therapy equipment
Radiation treatment
Radiosurgery
Radiosurgery - methods
stereotactic radiotherapy
Surgery, Computer-Assisted
Surgery, Computer-Assisted - methods
synchrotron radiation
Synchrotrons
Therapeutic applications, including brachytherapy
Tissues
tumours
X‐ray applications
X‐ray effects
X‐ray imaging
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Summary: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 theMCNPX 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
ISSN:0094-2405
2473-4209
DOI:10.1118/1.3327455