DOSM 315 Physics for Medical Dosimetry I • 5 Cr.


Explores the fundamentals of radiation therapy physics with special attention to nuclear transformations and decay, x-ray production, radiation generators, interactions of ionizing radiation, x-ray beam quality, measurement of absorbed dose, dose distribution and scatter analysis. Prerequisite: Acceptance into the program.


After completing this class, students should be able to:

  • Calculate the decay constant, mean and half-life of a radioactive source
  • Identify internal structure of an x-ray tube and identify the two different mechanisms by which x-rays are produced.
  • Identify key components and differential mechanisms between current linear accelerator technology and historical delivery units.
  • Define the difference between transmission and geometric penumbra and be able to calculate geometric penumbra.
  • Define the terms attenuation and linear attenuation coefficients and apply these terms to Half and Tenth Value Layers.
  • Discuss the differences between coherent scattering, photoelectric effect, Compton effect, pair production and annihilation radiation and their associated energy ranges.
  • Calculate the incident photon energy, scattered photon energy or scattered electron energy for Compton interaction.
  • Describe the dependence of various interactions’ on atomic number
  • Calculate equivalent attenuation using electron density across multiple mediums.
  • Define the stem effect and the two root causes for this effect.
  • Define the unit of measurement, the Roentgen, and its relationship to electronic equilibrium within a free-air ionization chamber.
  • Calculate the temperature and pressure correction for exposure measurement
  • Calculate the exposure in Roentgens for a field of radiation.
  • Calculate the HVL for a radiation beam
  • Discuss the limitations to HVL alone as a measure of beam quality in superficial and orthovoltage range units.
  • Define the relationship between kerma, exposure and absorbed dose.
  • Calculate dose to any medium using the f-factor and define the change in the f-factor as function of energy.
  • Analyze the TG-21 and TG-51 recommendations for absorbed dose measurements and calibration.
  • Calculate the dose to a prescribed depth using Percentage Depth Dose charts (PDD).
  • Calculate the equivalent square for an irregular field size.
  • Calculate the Tissue-Air Ratio (TAR) for a given clinical field size and depth.
  • Define the relationship between the Backscatter Factor and TAR.
  • Define the relationship between the TAR and PDD for a given beam.
  • Calculate the Scatter-Air Ratio using TAR data.
  • Define the Clarkson method of dose calculation for irregular fields.