Dosimetric Comparison with Different ARC and Beam VMAT Optimization in the Monaco Treatment Planning System

Introduction: The Monaco Treatment planning system provides the sequencing parameter ‘Max Number of Arcs’ in volumetric modulated arc therapy optimization. Using this, we can have a maximum of four arcs per beam. In this study, different arc and beam combinations are evaluated. Aim: To compare the dosimetric parameters of VMAT plans in oral cavity radiotherapy treatment planning using single beam multiple arcs and two beam single arcs, and thereby evaluate the effects of the ‘Max Number of Arcs’ optimization parameter in the Monaco treatment planning system. Materials and methods: Data from 10 previously treated head and neck cancer (oral cavity) patients were used for this study. For each patient, four plans were generated with different arc and beam arrangements (one beam with 4 arcs, one beam with 3 arcs, one beam with 2 arcs, and two beams with a single arc). Plans were generated with similar constraints and dose coverage objectives, and all plans were normalized to receive 95% of the PTV receiving 100% of the prescription dose. Plans were evaluated using different dosimetric parameters. Results and discussion: Using one beam with four arc optimization parameter, homogeneous plans were generated, compromising delivery time and MU. One beam three arc plan gives comparative dose coverage, reduced delivery time, and MU compared to one beam four arc plan. One beam with two arc shows poor coverage. Two beam, one arc doesn’t give the expected result with a higher Dmax value, but MU and delivery times are on par with the three beam, one arc plan. Conclusion: For complex head and neck plans, one beam with three arcs is recommended for obtaining the optimum dose coverage, delivery time, and MU. This leads to reduced patient-on-table time and quality assurance time.