Sci—Wed PM: Delivery—06: Management of Intra‐Fraction Organ Motion: First Performance Evaluation of an Experimental Dynamic Tumor Tracking System
The management of intra‐fraction organ motion is an area of active research in medicalradiation physics. We present the development of a technical platform that allows a dynamic real‐time adaptation of radiation fields to moving radiation targets with a multi‐leaf collimator. The system consists of a dynamical control‐loop for an experimental MLC160 integrated with an ARTISTE linear accelerator. The information about the real‐time tumor position is taken directly from potentiometers that steer the movement of phantoms in the iso‐centric reference frame of the linear accelerator. As a second input the real‐time signal of the 4D‐tumor tracking device of CalypsoMedical Inc. can be employed. The performance of the system is evaluated by experimental studies with two moving phantoms: i) 2‐dimensional movements of the radiation target are simulated by a block of RW3 slabs that moves perpendicular to the treatment beam with different amplitudes for each direction of motion ii) an anatomically shaped lung phantom for which a solid tumor of RW3 is embedded in a low‐density material can be moved periodically in the cranial‐caudal direction with different amplitudes and frequencies. The irradiation of both phantoms can be analyzed by film dosimetry. The geometrical accuracy of the radiation field adaptation was measured with an EPID and gafchromic films imbedded into the phantoms. In a first test we have determined the latency of the complete system to approximately 500 ms; however a geometrical tracking accuracy within few millimeters could be established for periodical target movements of 2–4 cm amplitudes and characteristic breathing frequencies.