Dosimetric comparison of 2.5 mm vs. 3.0 mm leaf width micro-multileaf collimator-based treatment systems for intracranial stereotactic radiosurgery using dynamic conformal arcs: Implications for treatment planning

Purpose. The objective of our study was to explore any significant dosimetric differences between different leaf width (3.0 mm vs. 2.5 mm) micro-multileaf collimator (mMLC)-based treatment systems for intracranial stereotactic radiosurgery using dynamic conformal arcs (DCAs). Materials and methods. The systems included a 3 mm leaf width mMLC (m3) mounted on a nondedicated linac, and the Novalis Tx system with an integrated 2.5 mm width mMLC (HD120). Thirty plans for brain metastases were replanned for both systems using a uniform method for target definition and treatment planning for baseline comparison. Results. The target coverage values for the 80% isodose surface (IDS) and the D95 values in the HD120 plans were significantly lower than those for the m3 plans. The ratios of lower isodose volumes to the target for the HD120 were smaller than those for the m3. When a 1 mm leaf margin was added to the HD120 plans, these differences were reversed, but statistically significant differences were still observed. Conclusion. Significant dosimetric differences were observed between these systems. Different planning methods are required for the two systems to attain similar target coverage values with selected IDS, which can be achieved by adjusting the leaf margin with 0.1 mm increments or isocenter dose settings.