Electron Beams: Physical Principles in addition to Dosimetry Kent A. Gif as long as d, Ph.D. Departm

Electron Beams: Physical Principles in addition to Dosimetry Kent A. Gif as long as d, Ph.D. Departm www.phwiki.com

Electron Beams: Physical Principles in addition to Dosimetry Kent A. Gif as long as d, Ph.D. Departm

Hung, Melissa, Founding Editor has reference to this Academic Journal, PHwiki organized this Journal Electron Beams: Physical Principles in addition to Dosimetry Kent A. Gif as long as d, Ph.D. Department of Radiation Physics UT M.D. Anderson Cancer Center kagif as long as d@md in addition to erson.org Medical Physics III: Spring 2010 Physical aspects Electron Interactions Inelastic collisions atomic electrons (ionization & excitation) nuclei (bremsstrahlung) Elastic collisions w/ atomic electrons w/ nuclei

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Electron Interactions Collisional (ionization in addition to excitation) Energy loss electron density (Z/A) Radiation losses (bremsstrahlung) Energy loss Energy & Z2 Electron Interactions Mass Stopping Power (S/r): Rate of energy loss (units: Mev-cm2/g) Collision losses (ionization in addition to excitation) & radiation losses (bremsstrahlung): Electron Interactions Restricted Mass Stopping Power (L/r)D: AKA LET (linear energy transfer) or energy loss per unit path length ( as long as local absorption not radiated away) E < D Electron interactions Absorbed dose Fluence Dose Electron beam characteristics Rapid rise to 100% Region of uni as long as m dose (proximal 90% to distal 90%) Rapid dose fall-off High surface dose Clinically useful range 5-6 cm depth Electron Energy Specification (the average energy of the spectrum) (most probable energy @ surface) (average energy at depth z) Electron Energy Specification Energy specification: R50 - depth of the 50% dose Rp - maximum range of electrons From: Khan Electron Energy Specification Average Energy (E0): Most Probable Energy (Ep0): Energy (Ez) at depth z MDACC 21EX AAPM TG-25 Med Phys 18(1), 73-109 (1991) Determination of Absorbed Dose Calibration in water with ion chambers ADCL-calibrated system Cylindrical-chamber reference point located upstream of the chamber center by 0.5 rcav Reference conditions 100 cm SSD as long as a 1010 cm2 field Formalism: Depth-Dose Distribution Dose is calculated from ionization measurements: M is ionization is the ratio of water-to-air mean restricted stopping powers is the ratio of water-to-air fluence Prepl is a chamber replacement correction Clinical aspects in addition to dosimetry Characteristics of clinical electron beams X-Ray Contamination Surface Dose Depth of 80% Dose Depth of 50 % dose Depth of 90% Dose Characteristics of Clinical Electron Beams Surface Dose: Surface dose increases with increasing electron energy From: Khan Characteristics of Clinical Electron Beams Depth of the 80% Dose: Equal to approximately Enom/2.8 : Depth of 90% is approximately Enom/3.2 MDACC 21EX Characteristics of clinical electron beams Practical Range: Equal to approximately 1/2 nominal energy: Energy loss is about 2 MeV / cm MDACC 21EX Characteristics of clinical electron beams X-Ray Contamination: Increases with energy: Varies with accelerator design Defined as RP+2 cm MDACC 21EX Characteristics of clinical electron beams Accelerator design variations Penumbra X-ray Contamination From: Tapley Characteristics of clinical electron beams Penumbral Effects: Low energies show expansion of isodose values High energies show constriction of high isodose values with bowing of low values. Electron Beam Dosimetry Isodoses (6 MeV) Electron Beam Dosimetry Isodoses (20 MeV) Electron Beam Dosimetry PDD- effect of field size (6 MeV) Hung, Melissa Hyphen Magazine Founding Editor www.phwiki.com

Electron Beam Dosimetry PDD- effect of field size (20 MeV) Electron Beam Dosimetry Beam abutment Electron Beam Dosimetry Beam abutment- electrons (6 & 20 MeV)

Electron Beam Dosimetry Beam abutment- electrons (6 & 12 MeV) Electron Beam Dosimetry Beam abutment- electrons Electron Beam Dosimetry Beam abutment- photon & electron (6 MeV & 6 MV)

Electron Monitor-Unit Calculations – Sample Problems Electron Monitor-Unit Calculations – Sample Problems Electron MU Sample Problems

Hung, Melissa Founding Editor

Hung, Melissa is from United States and they belong to Hyphen Magazine and they are from  San Francisco, United States got related to this Particular Journal. and Hung, Melissa deal with the subjects like Asian Interest; United States

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