The dependence of interplay effects on the field scan direction in PBS proton therapy.

The dependence of interplay effects on the field scan direction in PBS proton therapy. Phys Med Biol. 2019 Mar 20;: Authors: Fattori G, Klimpki G, Hrbacek J, Zhang Y, Krieger M, Placidi L, Psoroulas S, Weber DC, Lomax AJ, Safai S Abstract The literature is controversial about the scan direction dependency of interplay effects in pencil beam scanning (PBS) treatment of moving targets. A directional effect is supported by many simulation studies, whereas the experimental data are mostly limited to simple geometries, not reflecting realistically clinical treatment plans. We have compared increasingly complex treatment fields, from a homogeneous single energy layer to a more modulated lung plan, under identical experimental settings, seeking evidence for differences in motion mitigation due to the selection of primary scanning direction. In total, 120 experimental samples were taken, combining two primary scan directions and three rescanning regimes with different motion scenarios. 4D dose distributions were measured in water with a moving ionisation chamber array and compared to those of a stationary delivery using 2D gamma analysis. Each plan has been verified twice for the same rescanning regime and motion scenario, changing the meandering direction in between to scan perpendicularly to, or along, the target motion. Additionally, machine log files of the lung plan, together with 4D CT data, were used to calculate the dose distribution...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research