Planning quality and delivery efficiency of sMLC delivered IMRT treatment of oropharyngeal cancers evaluated by RTOG H-0022 dosimetric criteria

Abstract

The time required to deliver intensity modulated radiation therapy (IMRT) treatments can be significantly longer than conventional treatments, especially for the segmented multileaf collimator (sMLC) delivery system with a large record and verification (R&V) overhead. In this work, we evaluate the impact of the number of intensity modulated beams (IMB) and the number of intensity levels (IL) on the quality and delivery efficiency of IMRT plans, generated by Corvus planning system for sMLC delivery on a Siemens linear accelerator with Lantis R&V system. Detailed studies were performed for three image data sets of previously treated oropharyngeal patients. Treatment plans for patient 1 were developed using 5, 7, 9 or 15 evenly spaced axial IMB as well as one with 7 user-selected axial IMB, each using IL of 3, 5, 10 or 20. For patients 2 and 3, plans with 15 IMB and 20 IL were not attempted. A total of 42 plans were developed using three oropharyngeal cancer CT image data sets. Plan quality was evaluated by assessing compliance with the Radiation Therapy Oncology Group (RTOG) H-0022 protocol criteria and clinical judgment of the physician. Plan efficiency was accessed by number of segments of each plan. It is found that for our treatment planning and delivery system, an IMRT plan that uses a moderate number of IMB and IL, such as 7 or 9 IMB with 3 or 5 IL, would appear to be the optimal approach when both quality of the plan and delivery efficiency are considered. Based on this study, we have routinely used 9 IMB with 3 IL or 7 IMB with 5 IL for head and neck patients. A retrospective comparison indicates that the delivery efficiency is improved on the order of 30% comparing to plans generated with 9 IMB with 5 IL.