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High-Energy Electrons for Radiation Treatments and Cancer Imaging SCIT Seminar Erica Cherry and Rebecca Fahrig 2/5/14 What is PHASER? Pluridirectional High-energy Agile Scanning Electron Radiotherapy New medical device for delivering faster, more accurate radiation treatments Uses a high-energy electron beam instead of a photon beam Ideally, lack of moving parts allows treatment in < 1 sec Why bother? Current radiation treatments take 5-20 minutes to deliver a full dose. Organs move during that time and healthy tissue can be irradiated. Right: Superposed views of a patient’s liver at different points in the breathing cycle K.K. Brock, “Imaging and Image-Guided Radiation Therapy in Liver Cancer,” 2011 FASTER = MORE ACCURATE! Preliminary Design Linear Accelerator structure Patient Table Treatment Area Preliminary Design 2 One linac line (100 MeV electrons) Treatment region 80-cm bore Preliminary Design 3 Array of linac lines Diverging electron beam Preliminary Design 4 IMAGING SYSTEM! beam stop Key imaging questions How can we rapidly image the cancer before treatment? How can we register the pre-treatment image to the image used for treatment planning and adjust the plan? How can we fit the necessary hardware into a limited space? How can we verify that the treatment was delivered to the correct location? Electron Imaging Using the treatment beam for imaging would eliminate additional patient dose Imaging with electrons has been dismissed in the past Thick tissue is opaque to low-energy electrons Coherent high-energy electron beams are made with expensive and unwieldy machinery High-energy electrons impart a high radiation dose PHASER already must include hardware for making VHEE– why not try it for imaging? Key Questions on Electron Imaging What is the energy distribution of high-energy electrons exiting inhomogeneous tissue? How much do electrons scatter in various materials? What dose to tissue is required to achieve observable image contrast? Does adding a contrast agent help? Electron Monte Carlo Simulation: Part 1 Question: can any useful image data be collected using a high energy electron beam? Monte Carlo simulation setup: Plane electron source Beam monitoring plane Inhomogeneous phantom Image plane (DATA HERE!) Conclusions from Phantom #1 Minimal soft tissue contrast Reasonable contrast with iodine and bone Question: is the contrast enough that we can see objects in the body when surrounded by other tissue? Electron Monte Carlo Simulation: Part 2 Plane electron source Beam monitoring plane Image plane (DATA HERE!) Cross section view: “Projection column” Total Energy Flux 4% difference Blood Bone Dilute Iodine Fat Medium Dense Iodine Muscle Gold Gold Collimated Energy Flux Restriction: no particles incoming at more than 10° relative to normal vector 6% difference Blood Bone Dilute Iodine Medium Dense Fat Iodine Muscle Gold Gold Conclusions from Phantom #2 Energy spectrum of electrons exiting realistic phantom is indistinguishable for different materials Energy flux may be distinguishable Collimation helps differentiate materials but decreases flux For 1010 incoming electrons/cm2, difference of 2 x 108 MeV/cm2 between regions (~0.16 mJ/cm2) Questions for Future Work Is there a type of detector that can distinguish between different materials? Is it possible to build a combined beam stopping and energy integrating detector? Can we use fluorescence at lower energies to distinguish materials?