Evaluation of CBCT based dose calculation in the thorax and pelvis using two generic algorithms
Rune Slot Thing, Rasmus Nilsson, Sean B. Andersson, Martin Berg, Mikkel Drøgemüller Lund
Abstract
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.