Comparison of IMRT planning with two-step and one-step optimization: a way to simplify IMRT.

Intensity-modulated radiotherapy (IMRT) plans are often complex, increasing the potential for dosimetric errors and prolonged treatment times. The purpose of this study is to evaluate the effectiveness and efficiency of one-step optimization as compared to conventional two-step optimization in inverse IMRT planning and to investigate the tradeoff between the number of segments and IMRT plan quality. Ten IMRT cases were studied, including five prostate patients and five nasopharynx patients. For each patient, seven research plans were generated with the same beam angles and objectives as the clinical plan using a commercial treatment planning system with the ability to perform one-step and two-step optimization. Two-step plans had the number of intensity levels set to 10, 5 and 3. One-step plans had the maximum number of segments set at 80, 60, 40 and 20 for prostate, and 100, 65, 50 and 25 for nasopharynx. When compared with two-step plans with similar numbers of segments, one-step plans resulted in lower MUs, higher homogeneity and conformal indices, and lower doses to sensitive structures. One-step optimization is an effective method for simplifying IMRT plans, resulting in a significant reduction in the number of segments for step and shoot delivery without significantly sacrificing plan quality.