ESTRO 2023 - Abstract Book

S1392

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ESTRO 2023

Results Good agreement was found between the doses calculated on CT and re-calculated on CBCT scans. For all phantoms mean PTV dose difference was below 0.5 Gy, with CBCT-based calculation resulting in slightly higher doses. Small dose differences were also observed in Dmean to surrounding OARs. Dose difference was below 0.5 Gy for all OARs analyzed for Plans 1, 3, 5 and 6. In the CBCT-based dose re-calculation for Plan 2 (configuration with multiple metal implants), the Dmean to the left parotid was underestimated by 0.6 Gy and the Dmean to the middle pharyngeal constrictor muscle was overestimated by 0.8 Gy. For Plan 4, the Dmean to a 0.5 cm ring around the PTV was underestimated by 0.6 Gy. All plans had excellent gamma agreement, 3%/1mm > 97%, and only Plan 2 had gamma agreement 2%/1mm < 94% (Fig. 2).