01 - A comparison of various scanned proton pencil beam delivery strategies for the treatment of moving targets

Purpose:The treatment of moving targets with pencil beam scanned proton therapy (PBS-PT) relies on repainting strategies to smooth out interplay effects. PBS-PT machines, such as ProteusPlus (PPlus) and ProteusOne (POne), deliver a continuous or a pulsed beam, respectively. In PPlus, non- or scaled repainting can be applied, while POne implies intrinsic repainting due to its pulsed delivery. We investigate here the efficacy of these two machine characteristics for the treatment of thoracic tumours.Materials and Methods:4D robust optimised PBS-PT treatment plans were calculated for eight non-small cell lung cancer (NSCLC) patients. All plans were delivered in dry runs at PPlus (with and without five times layered repainting) and POne facilities to obtain machine log files. By using these log files and verification 4DCTs per patient (acquired at different time points), a 4D robustness evaluation was performed towards setup and range errors, machine errors, anatomy changes, breathing motion, and interplay effects. Plan robustness was then assessed through the resultant voxel-wise worst-case dose.Results:Clinically relevant differences in voxel-wise worst-case dose distributions were observed between the PPlus and the POne plans (Fig. 1). In PPlus, repainting generally provided more robust plans. POne resulted in better target coverage than the PPlus repainted plans. A maximum voxel-wise worst-case V95(CTV) improvement from 50.30% (repainted PPlus) versus 94.57% (POne) was observed for patient case Pt.5 (Table 1).Conclusion:Repainting enables the mitigation of potential disturbing effects of PBS-PT for moving targets. The intrinsic repainting of POne showed to be more effective than the scaled repainting of PPlus to treat NSCLC.