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Background: Robust optimization has been suggested as an approach to reduce the irradiated volume in lung Stereotactic Body Radiation Therapy (SBRT). We performed a retrospective planning study to investigate the potential benefits over Planning Target Volume (PTV)-based planning., Material and Methods: Thirty-nine patients had additional plans using robust optimization with 5-mm isocenter shifts of the Gross Tumor Volume (GTV) created in addition to the PTV-based plan used for treatment. The optimization included the mid-position phase and the extreme breathing phases of the 4D-CT planning scan. The plans were compared for tumor coverage, isodose volumes, and doses to Organs At Risk (OAR). Additionally, we evaluated both plans with respect to observed tumor motion using the peak tumor motion seen on the planning scan and cone-beam CTs., Results: Statistically significant reductions in irradiated isodose volumes and doses to OAR were achieved with robust optimization, while preserving tumor dose. The reductions were largest for the low-dose volumes and reductions up to 188 ccm was observed. The robust evaluation based on observed peak tumor motion showed comparable target doses between the two planning methods. Accumulated mean GTV-dose was increased by a median of 4.46 Gy and a non-significant increase of 100 Monitor Units (MU) was seen in the robust optimized plans., Interpretation: The robust plans required more time to prepare, and while it might not be a feasible planning strategy for all lung SBRT patients, we suggest it might be useful for selected patients.

Purpose: This work examines the dosimetric performance of two algorithms creating a corrected CBCT (corrCBCT) and a virtual CT (vCT) implemented in a commercial treatment planning system., Methods: 60 patients distributed across all patient groups treated with curative intent at Vejle Hospital (breast, lung, prostate and anal/rectal cancer) were selected for the present study. Clinical treatment plans were recalculated on corrCBCT and vCT, as well as a reference CT (refCT) acquired as close in time to the CBCT image as possible. Recalculated doses were compared using gamma analysis, as well as by comparing D 98% , D 50% , and D 2% for all delineated targets and organs at risk., Results: High dosimetric accuracy is demonstrated on both the corrCBCT and vCT. Gamma 2%/2mm pass rates >98% were found for all patients except two outliers still having >93% pass rates. Equivalence of all evaluated dose metrics within ±1Gy was observed for all patient groups, while the pelvic patients additionally showed equivalence for all metrics within ±1% of the refCT dose. For the thoracic patients, equivalence within ±2.5% was established for all metrics except median dose to the ipsilateral lung, calculated on corrCBCT for the breast patient group., Conclusion: The corrCBCT and vCT images are shown in excellent dosimetric agreement with refCT images, and show high potential for future use for streamlined adaptive radiotherapy workflows., (Copyright © 2022 Associazione Italiana di Fisica Medica e Sanitaria. Published by Elsevier Ltd. All rights reserved.)