ESTRO 2023 - Abstract Book

S1444

Digital Posters

ESTRO 2023

Conclusion The poor performance observed in the PD verification is mostly caused by the energy dependence of the EPID (high Z phosphor) response, such that the imager response to the beam spectrum transmitted through closed MLC leaves is much lower than for the open beam spectrum, as several authors have pointed out (Med Phys. 2008;35(4):1267-1277). This issue is more important for 6 MV FFF beams because the FFF open beam is softer than the 6 MV beam. This issue is not taken into account by the PDIP algorithm. Refinement or ad hoc corrections are need for this algorithm and 6 MV FFF beams.

PO-1727 Impact of the dosimetric leaf gap on the AAA portal dose image prediction algorithm

J. Calvo-Ortega 1,2

1 Hospital Quirónsalud Barcelona, Radiation Oncology, Barcelona, Spain; 2 Hospital Quirónsalud Málaga, Radiation Oncology, Málaga, Spain Purpose or Objective The Eclipse treatment planning system offers portal dose image prediction (PDIP) for the 6 MV FFF energy using the AAA algorithm (AAA-PDIP). The aim of this study is to evaluate the impact of the clinical dosimetric leaf gap (DLG) on the AAA PDIP algorithm used for patient-specific quality assurance. Materials and Methods A TrueBeam linac equipped with the High Definition (HD) MLC and the aS1200 EPID was used. The Acuros v. 16.1 algorithm is clinically used in our department for treatment planning. The DLG and MLC transmission (T) values required by Acuros for 6 MV FFF beams were optimized for clinical plans by chamber measurements to achieve measured-calculated dose differences within ±2%. Values of DLG= 1.25 mm and T= 0.01 were found.