Abstract
Purpose:To validate dose calculations in a rigidly moving object.Methods:An off‐line version of the TomoTherapy™ dose calculation software was extended to allow dose calculation for rigidly moving objects. The interface allows users to extract the necessary data from TomoTherapy patient archives to perform an off‐line dose calculation, and to specify arbitrary translational motion by creating a text file with a column for time, and columns for x, y, and z translations. Film measurements were performed using a phantom that was rigidly moved with the same motion profile as used in the calculation. A variety of motion profiles were studied and the motion profiles were applied to delivery plans with varying field sizes (1, 2.5, and 5 cm) and with dynamic jaws and static jaws.Results:Calculations matched measurements to within 2% or 1 mm for the variety of motion profiles studied. A 4‐mm step motion in the longitudinal (IEC‐Y) direction timed to occur halfway through a 1 cm field‐width delivery resulted in a 29% decrease in both the calculated dose and measured dose in a central region of the dose profile. For a 5 cm field‐width dynamic jaw delivery, the 4 mm step motion resulted in a more broadly distributed reduction in dose of 8%. A 6 mm sinusoidal motion in the longitudinal direction with a 6 second period had a negligible impact on delivered dose for one particular delivery plan. Similarly, a step motion in the transverse direction (IEC‐X) had a negligible impact on delivered dose other than to shift the dose volume.Conclusion:A research version of the TomoTherapy™ dose calculator can accurately calculate dose for a rigidly moving object. Further studies with more clinical motion traces and with clinical treatment delivery plans will yield valuable insight into the impact of motion on the delivered dose.
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