SU-E-T-392: Physical Characterization and Clinical Experience for An Integrated 160-Leaf Multi-Leaf Collimator with a New Concept Design

Abstract

Purpose: A new concept design of an Elekta radiation head (agilityTM) has an integrated 160-leaf multi-leaf collimator (MLC). The agilityTM consists of 160-leaves with 90 mm height and 5 mm width at isocenter. The MLCs are located at a stair head in a linear accelerator head and works as X-jaws. The purpose of this study is to conduct a measurement and treatment planning study on the dosimetric properties and delivery advantages of agilityTM. Methods: The dosimetric characterizations including dose leakage, leaf position accuracy, tongue-and-groove (T&G) effect, and field penumbra were evaluated using 4, 6 and 10 MV photon beams. Furthermore, clinical plans such as intensity modulated radiation therapy were tested using a Monaco (Elekta) treatment planning system (TPS). Results: The leakage was remarkably low with 0.44% (average) and 0.47% (maximum) for 10 MV due to a new design principle of tilted leaves. However, the T&G effect occurred due to the tilt and it was approximately 20.8% (average) and 22.3% (maximum) for 6 MV. The leaf position accuracy was within 0.5 mm for all gantry angles and each MLC. The penumbra width was greater with a wider field size and the maximum width of 8.5 mm for 4 MV. As for clinical plans, dose distributions for all plans with TPS were in good agreement with measurements. The absolute dose at isocenter agreed with TPS in less than 2%. The comparison of gamma analysis was more than 95% pass rate with criteria of 3 mm/3%. High position designed MLCs made wider penumbra but instead, it can gain a large head clearance. Conclusion: The experimental results in this study indicate that the dosimetric characteristics of agilityTM are capable of improving the quality of dose delivery. The agilityTM provides a large head clearance, the flexible and safe radiotherapy.