ESTRO 2023 - Abstract Book

S1635

Digital Posters

ESTRO 2023

For our cohort of 14 patients this gave a total of 227 010 simulated treatment scenarios per planning method that were used for evaluation.

Results Both FLU and IRN achieved at least 95% of the intended dose in more than 90% of the simulated treatments, despite tumor motion amplitudes being larger in the cine-CT images than in the 4DCT and patient shifts being applied. The ISD method led to consistently higher D50% doses than the intended one. Confidence intervals at 80% for CTV D50%, in Gy, were [51.9, 54.6] for FLU, [51.7, 54.6] for IRN and [57.1, 63.5] for ISD.Our study shows that the tumor motion during free breathing not covered by the 4DCT gives a risk of underdosage but that this effect is small when planning for an additional PTV margin together with 4DCT derived ITV. Further, it was shown that the PTV prescription level for ISD corresponded poorly to the intended CTV dose and we do not recommend PTV based prescriptions when a certain CTV dose is desired. Confidence intervals at 80% for CTV HI were [0.08, 0.22] for FLU and [0.16, 0.23] for IRN and ISD. Further advantage of FLU over IRN and ISD was lower dose to the ipsilateral lung.