Medical Physics 501 Qualifying Oral Exam Flashcards

Flashcards for Medical Physics 501 Qualifying Oral Exam Review

Dosimetry Issues

Conversion to charged particles, ionization vs. excitation, dominance of dosimeters, small amount of energy, no general relation between dose and fluence unless some spatial equilibrium.

Gray Unit

Small unit where 1 Gy = 1 J/kg. A 30cc tumor given 60Gy will only add 0.5 calories to the body.

Differences between , tr, en

: Linear attenuation coefficient, tr: energy transfer coefficient, en: energy absorption coefficient; for diagnostic energies, tr = en

Attenuation Equation

 = 0 * e^(-dl), where  = (N / A)

Photoelectric Effect

Interaction with the whole atom resulting in a photoelectron with energy Te-  h - Eb

Compton Scattering

Interaction with a single electron following the description e = Z * ae

Pair/Triplet Production

Requires Tavail = h - 2m0c2 energy for both pair and triplet, but triplet has a threshold of 4m0c2

Rayleigh Scattering

Coherent version of elastic scattering involving the whole atom, similar to Thomson scattering per electron but still elastic.

Photonuclear Interactions

Small cross-sections with an energy threshold based on binding energies.

Dose Creation

Created by charged particles that are either primary or secondary results of other interactions.

Unrestricted Stopping Power

Continuous slowing down, straight-ahead approximation, signifies no delta-rays events in the approximation.

Restricted Stopping Power

Considers hard collisions that make delta-rays that need to be tracked themselves individually. Needed for Spencer-Attix cavity theory.

Equilibrium Condition

Exists when what leaves a region is replaced with what comes in.

Transient Charged Particle Equilibrium

Dose is from secondary charged particles from photon interactions.

Dose Proportionality

Dose  Kc * depth dose, Kerma includes all energy losses

AF in Dose Calculations

AF = 0: just charged particle equilibrium at most; AF = 1: radiation equilibrium, and safe to assume charged particle equilibrium.

Alpha Decay

Tunneling of helium nuclei from nucleus: X -> Y + He + Q

Beta Decay

Uses 'comparative half-life' to describe the probability of an electron or a positron leaving a neutron-rich nucleus.

Gamma Decay

Gamma released from excited nucleus with multiple radiation: X* -> X + Q

Cavity Theory

Determines how to relate dose in a cavity to dose in the surrounding medium based on charged particle equilibrium and interaction properties.

TG-21

Dosimetry protocol based on air kerma or exposure

TG-51

Dosimetry protocol based on water dose

Radiographic Film

Integrated dosimeter which relies on oxidation-reduction of silver halide.

Geiger Counter

Pulsed dosimeter that operates in the Geiger region of the voltage curve.

Rossi Detectors

Used in neutron dosimetry to obtain LET spectrum.

Kerma-factor

Used instead of Kerma in neutron dosimetry.