03 - Treatment Machines and Generators I

03 - Treatment Machines and Generators I - Lecture #3...

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Lecture #3 Treatment Machines and Generators - 1 Tarun K. Podder, PhD, DABR Department of Radiation Oncology Brody School of Medicine Leo Jenkins Cancer Center East Carolina University January 18, 2011
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2 Treatment Machines Production of X-rays -- X-ray tube Electrons Target Cathode (-) Anode (+) High voltage supply Glass envelop Thermionic emission
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3 Treatment Machines: x-ray generation Khan (Ch 3)
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4 Treatment Machines: x-ray generation Why tungsten is chosen as filament material and target material? Efficiency = = 9 10 -10 Z V X-ray energy produced Electron energy deposited (limited to a few MV) Tungsten Z=74 e.g. 100KV efficiency < 0.7% melting point = 3370 C
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5 Treatment Machines: x-ray generation Anode design line focus principle Focal spot: the apparent source of x-rays in the tube Small enough to produce sharp image (focal spot = 0.1x0.1 mm 2x2 mm) Large enough to tolerate a high heat loading A Electrons a = A Sin θ ( θ = 6-17 degree) θ Anode target X-ray For a diagnostic x-ray machine Anode heel effect Anode stronger x-ray Electron from cathode weaker x-ray
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6 Treatment Machines: x-ray generation • High energy x-ray therapy machines use transmission type targets. • Target is larger compared to that of diagnostic x-ray (θ≤30 0 , focal spot = 5x5 mm – 7x7 mm). Anode design - Stationary anode Tungsten, Molydbenum, rhodium Rotating anode increase the effective target area, raise heat capacity Electrons X-ray Transmission type target For a therapy x- ray machine Rotating target Electrons Anode Cathode X-ray
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7 Treatment Machines: x-ray generation Circuit diagram of a self-rectified x-ray unit half-wave rectification full-wave rectification Typical operating characteristics of x-ray
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8 Physics of x-ray production -- electron interaction What happened when electron hit a target? When they travel through medium, how do they interact with atoms? Heat + X-rays Coulomb force interaction Inelastic collision lose energy Elastic collision energy redistributed, but not lost
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9 What happened when electron hit a target? When they travel though medium, how do they interact with atoms? Heat + X-rays Coulomb force interaction Inelastic collision Elastic collision With nucleus With atom electrons With nucleus With atom electrons Bremsstrahlung ionization and excitation scattering Characteristic x-rays Physics of x-ray production -- electron interaction
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10 When electron collides with atom electrons: Excitation: atom electron is energized to higher energy state.
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This note was uploaded on 01/21/2012 for the course PHYS 6720 taught by Professor Hu during the Spring '10 term at East Carolina University .

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03 - Treatment Machines and Generators I - Lecture #3...

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