SU‐GG‐T‐529: Pre‐Clinical Evaluation of a 4D Tracking DmMLC‐Based Delivery to Lung Tumor

Purpose: The aim of this study is to provide a pre‐clinical evaluation of four‐dimensional tracking radiation therapy to lung tumor using a prototype tracking system. The evaluation was based on films dosimetric analysis, time delay measurements and treatment planning DVH analysis by using two types of dynamic phantoms. Method and Materials: The key component of the 4DTRT system was a prototype of TrackBeam. It consists of an image processing tools and a first‐of‐its‐kind dual‐layer micro MLC. DmMLC has two layers of orthogonal leaves which provide advantages in speed and conformality when forming beam aperture for tracking. The TrackBeam was mounted to a Varian Linac and connected to a workstation which process the online MV fluence and controls each leaf's motion. A Quasar dynamic phantom was used for radiographic film irradiation with 4DTRT and also 3DCRT. The phantom has a Gafchromic film insert and a gold marker in the insert. It can move in Sinusoid mode as well as real patient respiratory cycle. Another tissue‐equivalent thorax dynamic phantom was used for DVH analysis after a phantom‐based 3DCRT planning and a 4DTRT planning developed respectively. Results: The synchronization of marker motion and the DmMLC leaf motion was achieved within less than 0.05 seconds. The films analysis indicated that total 29.91% over the tolerance of 5% and 5.09% of over the tolerance of 5% when the 3DCRT and 4DTRT films compared to a static film. The DVH comparisons indicate 4DTRT reduces significant dose to the Ring from 75% (80% volume) to 60% (50% volume). 4DTRT also reduces considerable amount dose to the total lung from 33% (30% volume) to 22% (22%). Conclusion: The 4D tracking using MLC provides a feasible solution delivering conformal dose to lung tumor and spare the surrounding tissue. Conflict of Interest: The work was partially supported by Initia‐RT medical device.