Po‐Thur Eve General‐08: Monte Carlo Simulation of Helical Tomotherapy

Abstract

Helical tomotherapy represents the state of the art in intensity modulated radiation therapy (IMRT) and image guided adaptive radiotherapy (IGAR). This work is aimed at carrying out Monte Carlo (MC) dose calculations of tomotherapy deliveries to real phantom and virtual phantom/patient CT data. All MC calculations are performed with the EGSnrc‐based MC simulation codes, BEAMnrc and DOSXYZnrc. Various MC parameters and variance reduction techniques were investigated and optimized. Single projection simulations are carried out to get percent depth dose (PDD) and beam profiles at various depths and lateral field dimensions. Simulations are compared with measured results taken with an A1SL ionization chamber in a water tank. A complex delivery was simulated with the 64 leaf binary multileaf collimator (MLC) modulating at fixed radiation angle for a solid water phantom. Further, a rotational treatment plan to a cheese phantom CT data set was also simulated. Simulations are performed by taking the sinogram (leaf opening vs. time) of the treatment plan and decomposing it into different projections, each of which is segmented further into several opening configurations with different MLC settings and weights, which corresponded to leaf opening time. Then the projection is simulated with the result of sum of all of the opening configurations, and the overall rotational treatment is simulated with the result of sum of all of the projection simulations. Measured and simulated profiles and PDDs are found agree with each other well. Preliminary simulations of full treatment plans are also presented.