BLUE RIBBON POSTER THERAPY: 4D Robustness Assessment of Proton Lattice Radiotherapy for Large Lung Tumors Considering Robust Optimization and Tumor Motion
Abstract
Purpose
The Bragg peak of proton beam enables precise dose delivery and superior dose modulation in proton lattice radiotherapy (LRT), yet it remains susceptible to uncertainties. This study aims to investigate the impact of robust parameter settings and respiratory motion on IMPT–based LRT plans for bulky lung tumors.
Methods
Eight patients with bulky lung tumors were retrospectively analyzed. Target and OARs were contoured in the RayStation. An in-house script was developed in RayStation to generate sphere vertices. A non-robustly optimized plan (NRO plan) was generated without robust optimization. Both single-field and multi-field optimized IMPT-LRT plans were created. For each optimization, seven robust parameter settings (1mm-9mm) were applied to investigate the effect of setup uncertainty on LRT dose distribution. Four-dimensional dynamic dose (4DDD) was calculated by incorporating dynamic pencil beam scanning delivery with respiratory motion to evaluate the impact of motion on PVDR and dose distributions.
Results
PVDRs decreased as setup uncertainty parameters increased. Multi-field optimization resulted in slightly higher PVDR values. Most of the PVDR values were in the range of 2–4. Doses to OARs increased with larger setup uncertainties. Respiratory motion resulted larger PVDR deviations for single-field plan than multi-field plan. The 4DDD maintained the volume of high dose region inside GTV in single-field plan, while decreased in multi-field plan. The volume of high dose region decreased in 4DDD for both single-field and multi-field plans.
Conclusion
Increased setup uncertainty resulted in a reduction of the PVDR. Under respiratory motion, the single-field plan maintained high-dose coverage within the target but did not preserve the PVDR. In contrast, the multi-field plan retained the PVDR at the expense of high-dose volume within the target. With appropriate vertex contouring, neither single- nor multi-field plans introduced additional high-dose volume to the target boundary, thereby ensuring safe beam delivery in proton LRT during respiratory motion.