SU‐C‐108‐05: A Novel Technique to Evaluate 4D Dose Delivery to a Moving Tumor

Abstract

Purpose: Delivering highly modulated radiation beams accurately to a moving tumor is a difficult task; it is crucial to have tools to evaluate the efficacy of treatment delivery in such cases. We are reporting a novel technique to evaluate 4D dose delivery to moving tumors. We are also presenting an evaluation of RapidArc treatment delivery using this method. 4D position dependant dose is crucial because the peripheral regions of the tumor may not get adequate dose due to moving out of the MLC aperture. In our procedure we accomplish the position dependant dose evaluation by creating the effects of tumor motion as follows: instead of moving the tumor, we simulate to move the active MLCs in the direction opposite to tumor motion by the corresponding motion amplitude calculated at the time of delivery. Methods: Ten RapidArc plans were created, delivered at a Varian Trilogy unit and corresponding log files were recorded. A simulation, written in MATLAB, reads in the dynalog files, and calculates average time per each control point delivery with respect to beam initiation. A sinusoidal respiratory motion signal with a given maximum amplitude and period was implemented to obtain the motion amplitude at the time of delivery of each control point. A modified DICOM file was created where the active MLCs were moved to simulate the effects of tumor motion. This DICOM plan was reimported to Eclipse treatment planning system, and 4D dose was recalculated. To verify the accuracy of our simulation, a sample plan with 2.5cm motion amplitude was compared with delivery. Results: Simulation agrees well with the dose measurement (3% /3mm gamma acceptance of 98%). GTV under‐dosing is observed for large motion amplitudes, and small tumor volumes. Conclusion: A novel technique is developed to obtain delivered 4D dose distributions for moving tumors using machine log files.