ESTRO 2024 - Abstract Book

S3597

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

scanning, the narrow CBCT beam geometry with different scanning parameters was chosen. The CIRS DYNAMIC THORAX PHANTOM MODEL 008A was used to simulate a lung lesion of a 2cm sphere insert. CT and CBCT reconstructions of this phantom were obtained and transferred to the TPS. In planning, the structures of interest (the target volume and organs at risk) were delineated on the CT study set and then copied to the CBCT study set. A Stereotactic Ablative Body Radiation (SABR) lung plan was prepared following the SABR UK Consortium Guideline 2019 [5], planned with a prescribed dose of 55Gy/5#, MU=2078.33. CT plans were generated with clinical CT HU curves. These plans were recalculated using the CBCT reconstructions and RMI (CBCT) & CIRS (CBCT) calibration curves (see example - FIG.1.). , as well as for overridden densities from ICRU44 publication for comparison [6].

Fig.1. The TPS screen – 3 plans displayed for CT, M20 RMI(cal) CBCT, M20 CIRS(cal) CBCT, and DVH statistic.

Finally, the dose distribution and statistics for PTVs and OARs structures were compared using Consortium Guidelines 2019 for SABR lung cases.

Results:

The table Tab.1. displays the dose statistic metrics for the plan calculated using the CT images and CT calibration curve, and for the same plan recalculated using the CBCT scans and RMI/CIRS calibration curves as well for CBCT scans with synthetic overwriting applied. The dose distribution statistics were normalized to CT-based PTV and OAR volumes.