Minimizing static intensity modulation delivery time using an intensity solid paradigm

Purpose: A leaf sequencing optimization algorithm that minimizes the delivery time for a static intensity modulated field is presented. Methods and Materials: Sets of segments are created by intensity map operations subject to leaf collision constraints and tongue and groove effects. Each set's delivery time is evaluated as a function of leaf travel, beam on time, and the verify and record (V&R) overhead. The configuration with the minimum delivery time is chosen. As a test, optimization was done on three clinical cases of varying complexity. Results: Assuming 10 x 10-cm fields with an average of 17 intensity levels, the optimization technique reduced delivery times by 27% and 45%, when compared to rod pushing and power of two extraction, respectively. The treatment time for the optimal case with a V&R overhead of 4 s would be 11.5 min for 9 coplanar ports. Tongue-and-groove underdosages are removed, and the worst case leakage is 2% of the peak dose. Conclusion: Compared to previously reported leaf sequencing methods, the new optimization algorithm described here reduces treatment times for complex static intensity modulated fields, Additionally, leakage is minimal and no tongue-and-groove underdosage occurs. (C) 1999 Elsevier Science Inc.