Robust Planning for ITV-Based Lung VMAT SBRT
A Buczek1*, S Peca2, (1) Wayne State University, Detroit, MI, (2) McLaren Northern Michigan, Petoskey, MI
Presentations
PO-GePV-T-362 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To provide treatment planning tools that improve robustness to motion of ITV-based VMAT SBRT of lung cancer. In highly modulated plans, the interplay effect between tumor, gantry, and MLC motions may cause the target to be underdosed. However, more robust plans can be created to help deliver the tumoricidal dose.
Methods: A novel method of using the Aperture Shape Controller (ASC) and Monitor Unit (MU) objective to create plans more robust to motion is explored. From a clinical treatment, nine plans were created with varying ASC and MU objective settings. Each plan was delivered to four films: stationary, 10-, 20-, and 40-mm of superior-inferior motion to simulate breathing. First, gamma analysis between the stationary film and the TPS-calculated dose confirmed processing methods. Next, within each plan, gamma analysis between the stationary film and each motion film was performed.
Results: By comparing gamma scores, we show that certain ASC and MU objectives produce plans that, when delivered to a moving target, produce a dose distribution that is similar to that delivered to a stationary target. This is what we refer to as plan robustness to motion. Alone, a strict MU objective or a high ASC setting produce better gamma pass rates. The highest gamma pass rate was obtained combining high ASC with MU objective at 50% of unrestricted MU. A similar combination, low ASC and the same MU objective, was a close second.
Conclusion: For motion-encompassing lung SBRT, if tumor motion is more than about 1 cm, we recommend utilizing both of these treatment planning tools, limiting MU to up to 50% of the unrestricted value, and setting ASC to, or close to, the high setting.
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