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.