SU-F-BRB-06: Validation of Dose Calculation for Helical Tomotherapy with a Rigidly Moving Object




To validate dose calculations in a rigidly moving object.


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.


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.


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.