Medical Physics Seminar – Monday, January 28, 2013
How to accurately represent and measure a radiotherapy beam's spectrum
David W.O. Rogers (guest of Dr. Larry DeWerd)
Professor, Medical Physics, Physics Department - Carleton University, Ottawa, ON, Canada
Measuring the spectrum of photons from a radiotherapy beam is notoriously difficult. The transmission technique, used since the 30's, is in general ill- conditioned for clinical spectra. With a few measurement innovations, very careful measurements, a robust functional form to represent the spectrum and use of Monte Carlo simulations to calculate small corrections, my former student, Elsayed Ali, has shown how this method can be used accurately, without prior knowledge of the maximum energy.The measured transmission is such a stringent test of Monte Carlo calculations that Ali had to re-engineer the EGSnrc code to include photonuclear attenuation and more accurate photon cross sections.