Assessment of a diaphragm override strategy for robustly optimized proton therapy planning for esophageal cancer patients

Abstract

To ensure target coverage in the treatment of esophageal cancer, a density override to the region of diaphragm motion can be applied in the optimization process. Here, we evaluate the benefit of this approach during robust optimization for intensity modulated proton therapy (IMPT) planning.Materials and Methods: For ten esophageal cancer patients, two robustly optimized IMPT plans were created either using (WDO) or not using (NDO) a diaphragm density override of 1.05 g/cm 3 during plan optimization. The override was applied to the excursion of the diaphragm between exhale and inhale. Initial robustness evaluation was performed for plan acceptance (setup errors of 8 mm, range errors of ±3%), and subsequently, on all weekly repeated 4DCTs (setup errors of 2 mm, range errors of ±3%). Target coverage and hotspots were analyzed on the resulting voxel-wise minimum (Vw min ) and voxel-wise maximum (Vw max ) dose distributions. Results:The nominal dose distributions were similar for both WDO and NDO plans. However, visual inspection of the Vw max of the WDO plans showed hotspots behind the right diaphragm override region.For one patient, target coverage and hotspots improved by applying the diaphragm override. We found no differences in target coverage in the weekly evaluations between the two approaches. Conclusion:The diaphragm override approach did not result in a clinical benefit in terms of planning and interfractional robustness. Therefore, we don't see added value in employing this approach as a default option during robust optimization for IMPT planning in esophageal cancer.

Management of Motion and Anatomical Variations in Charged Particle Therapy: Past, Present, and Into the Future

“…ITVs can be constructed using different methods based on 4DCT images, including Max/Min inhale-based, MIP-based, and MidV-based. In addition, the concept of using density overrides within and around the ITV has been shown in recent simulation studies to improve dose coverage when the target moves through regions of highly variable density ( 78 , 79 ). Once an appropriate ITV has been determined, additional population-based margins reflecting setup and beam-specific range uncertainties are applied to generate a planning target for each beam ( 80 ).…”

Robustness assessment of clinical adaptive proton and photon radiotherapy for oesophageal cancer in the model-based approach

“…During treatment, weekly repeat 4DCTs were acquired and the ITV was redelineated on the average CT. The IMPT plan was evaluated both nominally, and robustly including 2 mm setup errors and 3 % range uncertainty [11,20,27,28]. The 2 mm setup error accounts for residual errors after patient alignment, such as intrafractional patient variation, isocentre and positioning accuracy.…”