Abstract
Due to anticipated clinical benefits, thoracic tumors are potential future indications for PBS-PT. However, the concern of plan robustness as a result of motion hamper its clinical implementation. Here we present a comprehensive evaluation of different planning strategies based on patient and machine specific data in order to define optimal PBS-PT protocols for lung and esophageal tumors. This study includes 3 non-small cell lung and 3 esophageal cancer patients with a planning as well as 5 weekly repeated 4DCTs available. For all patients, the CTV volume and motion were monitored throughout the treatment course. Layered rescanned (5 times) 3D and 4D robust optimized PBS-PT plans were created, and approved clinically. These plans were then delivered in dry runs at our proton facility to obtain machine log files, and subsequently evaluated through our 4D robustness evaluation method (4DREM). The 4DREM assesses the plan robustness for the combination of (1) setup and range errors, (2) machine errors, (3) anatomy changes, (4) breathing motion, and (5) interplay effects. The disturbing effects (2), (3), (4), (5) are considered by calculating subplan doses on particular 4DCT phases and performing 4D dose accumulation in all 4DCTs. The subplans were split from the nominal plan by retrieving log files information. For each evaluated plan, 14 4D accumulated scenario dose distributions were obtained, representing 14 possible full fractionated treatment courses. Only small differences in V95(CTV) between nominal and voxel-wise worst-case dose distributions were observed for all 3D / 4D robust optimized plans (consistently ≥ 99.89 %). Similarly, averaged Dmean(lungs-GTV) over all scenarios considered within the 4DREM changed only slightly (Table 1). For 6 patients with lung / esophageal cancer, our 3D / 4D PBS-PT planning protocol showed to be clinically suitable. After confirming these results in an extended patient cohort, we will proceed to investigate less conservative, more conformal planning strategies. The experience gained through comprehensive robustness evaluations based on patient and machine specific data is essential for the definition of optimal PBS-PT protocols for patients with thoracic tumors.Abstract 3762; Table 1Patient characteristics (mean ± SD volume and motion variations) and plan statisticsLungPt. 1Pt. 2Pt. 3Volume [cm3]108.2 ± 16.254.6 ± 5.755.6 ± 2.9Motion [mm]3.9 ± 0.84.6 ± 1.43.8 ± 1.23D4D3D4D3D4DDmean(lungs-GTV) [GyRBE] Nominal9.4010.478.497.359.078.47 Scenarios9.8310.688.617.598.927.96EsophagusPt. 4Pt. 5Pt. 6Volume [cm3]367.4 ± 14.0133.6 ± 10.3209.9 ± 2.6Motion [mm]6.5 ± 0.96.5 ± 0.73.1 ± 0.63D4D3D4D3D4DDmean(lungs-GTV) [GyRBE] Nominal4.304.281.381.411.911.98 Scenarios4.354.531.521.641.972.00 Open table in a new tab
Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
