An independent algorithm to check the monitor units calculation in radiosurgery
Luis Isaac Ramos, Rafael Martínez Monge, José Javier Aristu, and Leire Arbea Moreno
Department of Oncology, Clínica Universitaria de Navarra, University of Navarra,Avda Pío XII s/n. Pamplona, Navarre, Spain, Pc 31008
Double checking of the monitor units (MU) is an important step in the quality assurance (QA) process in radiosurgery. In this paper we propose the use of an independent algorithm constructed using the ellipsoid which best fits the measurements taken with the bubble head frame.
The monitor units calculated by this independent algorithm and the commercial planning system were compared in 40 patients treated with radiosurgery (57 isocenters, 320 arcs). The average relative difference was -0.2% +/- 2.1 (k=1). These results are better for the variance, -0.4% +/- 1.8 (k=1), when all the depths of the bubble head frame are measured and no arcs are calculated by extrapolation or when only one of these factors appear.
If there are missing values in the bubble head frame measurements and the model is extrapolated, the variance of the results is greater, 0.4% +/- 3.9 (k=1). The algorithm is reliable as a QA tool for linac radiosurgery.
CITATION Med Phys. 2008 Jan;35(1):48-51