SU‐E‐T‐603: Evaluation of MLC‐Based Robotic Radiotherapy

Purpose: A multi‐leaf collimator (MLC) system has been introduced for the CyberKnife M6 system, enabling conformal shaping of beam apertures in robotic radiotherapy. Through a multi‐disease site study, the potential for the use of MLC‐based robotic delivery is assessed for conventionally fractionated regimens. Methods: The InCise MLC, consisting of 41 leaf pairs, with leaf thickness of 2.5 mm at 800 mm SAD, and a maximum field‐of‐view field size of 120 mm × 100 mm was used in conjunction with the MultiPlan 5.0 platform for comparative planning study relative to the pseudo‐conical IRIS variable aperture collimator. Conformal avoidance technique with relaxed convergence was used for the optimization, and identical dose‐volume optimization parameters and normalization (95%) for the comparative studies. Disease sites, including the prostate, partial breast, and peri‐orbit carcinomas were evaluated, and the results were quantified with respect to total monitor units (MUs), treatment time, conformality, and dose‐volume coverage. Results: The MLC system results on average of 3– 4 modulated segments for a series of non‐coplanar nodes. Relative to plans generated by the IRIS variable aperture collimators, the MLC‐based plans resulted in a 38±10% reduction of both the MUs and treatment time. While similar dosimetry is achieved by both systems, for a dose rate of 1000 MU/min, it is shown that treatment times of less than 20 minutes are possible for most conventionally fractionated treatments with the MLC system. Conclusion: A limiting factor in the adaptation of the robotic delivery for conventional radiotherapy has been the prolonged treatment times. The introduction of compact MLC fixture enables reduction of MUs and treatment time, making conventionally fractionated treatments feasible to more efficiently leverage the higher delivering accuracy and intrafraction motion correction capabilities of robotic delivery.