Student presentation:

“Development of a hybrid alanine-calorimetry absorbed dose standard for linac electron beams”

The NRC primary standard water calorimeter is well-established for measuring dose to water in cobalt-60, linac photon beams and high-energy

(18 MeV and 22 MeV) linac electron beams.  However, for lower energy electron beams, given the short range of electrons and the physical dimensions of the calorimeter, it is impossible to perform measurements at the reference depths in water. To extend the measurement of absorbed dose to lower energy electron beams, an alternative system is required. The goal of this work is to establish a hybrid absorbed dose standard for linac electron beams by calibrating alanine against secondary standard ionization chambers, with calibrations traceable to primary standard water calorimeter measurements in high-energy electron beams, and subsequently using alanine in low-energy electron beams to determine absorbed dose.

This method requires that the response of alanine be energy-independent, which was verified in this work using Monte Carlo calculations of absorbed dose to alanine and absorbed dose to water for the electron beam energies investigated.  Ionization chambers calibrated against alanine in electron beams yield results for beam quality conversion factors that are in good agreement within ~1 % with literature data for five ionization chambers investigated.

By Rodi Surensoy

Department of Physics, Carleton University

Supervisor: Dr. Bryan Muir, National Research Council

Member presentation:

“Development and clinical applications of a 4D dosimetry system”

Organ motion is of particular concern in the treatment of lung and abdominal cancers, where breathing induces large tumor displacement and organ deformation. Many technological innovations developed over the years help to mitigate inter- and intra-fraction organ motion. 4D radiation therapy is the ultimate approach to organ motion management.

In this seminar, I will present the development and clinical applications of the 4D dosimetry system which can be used as an end-to-end or in vivo QA tool for 4D radiation therapy.

By Dr. Joanna Cygler

The Ottawa Hospital Cancer Centre