Room: AAPM ePoster Library
The Synchrony system allows for target tracking and motion correction using the Radixact Tomotherapy system. Before clinical implementation, evaluation of the system performance was undertaken.
This study evaluates the accuracy of the Synchrony motion correction for the “respiratory” and “respiratory with fiducials” tracking modes using a Delta4 phantom and Hexamotion stage. EBT3 film was also used to allow for increased resolution and comparison to Delta4 values. Custom inserts were designed and 3D printed to allow for target tracking using both a dense silicon rubber plug and triangular fiducial arrangement. The planned dose was delivered to a stationary phantom and a moving phantom both with and without motion correction enabled. The dose delivery changes were evaluated using the gamma index (2%, 2mm, 10% threshold) for the Delta4 and film placed in horizontal and vertical orientations. 1D motions in the y plane only (jaw correction) and x-z plane only (MLC correction) were evaluated separately.
With increasing phantom motion the delivered dose distribution became increasing distorted, reflected in low gamma pass rates. For the respiratory tracking mode Delta4 data shows an increase in pass rates of 4.4 % for 2.5mm y-direction motion, 16.6% for 5mm motion and an average increase of 74% for motions =7.5mm. For xz-motions a benefit was found when the motion exceeded the MLC leaf width of 6mm at isocenter, with an average increase in pass rate of 9.8%. Measured pass-rates were above 99% for all corrected plans. Analysis of film data shows similar improvement.
These results clearly show the benefit of jaw tracking using Synchrony and to a lesser extent the benefit of MLC tracking, due to the limited MLC resolution. Further investigation of more complex motions and changes in breathing patterns will be undertaken.