Mohammad Salehpour
Professor
The University of Texas MD Anderson Cancer Center
Department of Radiation Physics
Research Theme: Convergent Radiation
Small Animal Irradiator Project
Research into the development of a compact, variable dose rate, variable precision small animal irradiator using a novel miniature x-ray source based on carbon nanotubes. The long-term goals of the project include Simulation, Prototyping, and validating a high dose rate, low energy, directional x-ray tube no more than several centimeters long. From there, a collimating apparatus will be designed that arranges several of these sources in a converging beam geometry with individual control over each source’s exposure rate and distance from the target to create variable dose rates and variable beam sizes. A further aims of this work are to have an irradiator capable of FLASH dose rates at one setting and ultrafine beam delivery on another setting, complete with 4D staging, treatment planning software, a robust 3-dimensional dose painting algorithm, and validated QA routines. This invention will allow preclinical research to access far more of the modern radiotherapy parameter space than currently accessible with commercial irradiators.
Currently, we are in the stages of designing the miniature x-ray source. Through Monte Carlo simulation we have proven the advantageous dosimetric properties of our proposed geometry. Now we are in the process of designing the electrodes, simulating the electron transport, and calculating the heat transfer against various voltage waveforms prior to construction of the x-ray tube. Next steps include partnering with an engineering form to develop a prototype of the source for experimental evaluation and characterization.
An IDR (Invention Disclosure Record) has been filed with the Office of Technology Transfer.
Converging (focused) X-Ray Radiotherapy
MD Anderson has formed a strategic alliance partnership with the Convergent Radiotherapy and Radiosurgery (CRNR Ltd.) of Israel, to develop a novel focused x-ray radiotherapy device.
MDACC and CRNR strategic alliance Press Release
CRNR Ltd. has a developed a lens that produces a converging beam of x-rays from a diverging source such as that from a conventional x-ray tube. The nature of the physical process that produces the reflected x-rays within the lens structure results in a nearly monoenergetic beam produced from a polyenergetic radiation source. Such a novel focused monoenergetic beam can produce highly localized doses of radiation within the target with significantly decreased surface dose. The whole system, x-ray source and lens, is mounted on a robotically controlled arm which is used to manipulate the focal spot and paint conformal dose distributions.
MD Anderson’s contribution to the CRNR development is multi-faceted. We have recently installed the generation 2 prototype of the lens and x-ray tube. We are currently performing a wide range of measurements to characterize the beam in clinically relevant materials. We are also preparing to perform cell irradiations experiments. Additionally, we are contributing to dosimetry development for this system by establishing a collaboration with Medscint inc. (Québec, Canada) in order to evaluate a small-field scintillation dosimeter for the CRNR beam. We also have ongoing work to perform Monte Carlo simulations of the CRNR system which involves developing a novel Geant4 application incorporating Bragg diffraction as a Geant4 physics process. We are also contributing to the academic dissemination of the novelty of the system. Our first manuscript on this work was published in Nature Scientific Reports:
Analysis of a novel X-ray lens for converging beam radiotherapy.
Additional manuscripts have been submitted to Physics in Medicine and Biology (PMB).
Converging (focused) High Energy Electron Radiotherapy
A novel electron beam delivery system is being researched and proposed that uses Very High Energy Electrons (VHEE) to produce a localized spot of high dose within the target volume through a technique referred to as Magnetically Optimized Very High Energy Electron Therapy (MOVHEET). This high dose region is dynamically controlled to produce a distribution of dose within the tumor volume that is higher than surrounding normal tissue which results in greater normal tissue sparing and a larger degree of tumor control. The delivery system is based on the principle of dynamically focusing a beam of 50 – 250 MeV electrons to a desired target depth determined by a radiation treatment plan dose distribution where the output of the focusing system is a uniformly symmetric beam with a focusing angle that results in a low beam density at the patient surface producing low entrance dose. A set of quadrupole magnets will be used for dynamically controlling the focal spot depth of the electron focusing system to alter the electron trajectories to produce the desired beam behavior.
A wide range of simulations and analysis of the parameters affecting converging beam dose delivery has been completed. Furthermore, additional simulations have been completed to characterize the basic parameters required for the quadrupole delivery system. A patent on said delivery system has been applied for and granted. Collaborations with accelerator physicists and manufacturers have been established and parameters for a novel VHEE accelerator have be determined. A licensing agreement has been reached with Empyrean Medical Systems (Boca Raton, FL) to develop the MOVHEET concept into a commercial radiotherapy device.
Education & Training
PhD, University of Missouri-Columbia, 1991