# DOSM 315 Physics for Medical Dosimetry I • 5 Cr.

## Department

## Description:

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.

## Outcomes:

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 interactionsâ€™ 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.