Figure 1.

Schematic indicating prototype linac components and biology-guided beam delivery. (a-c) Image acquisition steps, (d-f) image reconstruction and analysis, and (g) beam delivery. (h-i) The difference between standard target volumes and biology-guided radiation therapy (BgRT) target volumes. In both cases, plans are optimized to cover the PTV. The major difference is that the BgRT approach does not require an internal target volume (ITV) to account for internal tumor motion. Instead, internal motion is tracked during delivery within a valid boundary defined by the biology-tracking zone (BTZ). Abbreviations: CTV = clinical target volume; GTV = gross tumor volume; PET = positron emission tomography; PTV = planning target volume.