ESTRO 2023 - Abstract Book

S1485

Digital Posters

ESTRO 2023

Conclusion A preliminary dataset of a standardization project involving several Italian departments was presented. The pilot center values were consistent with the reference one in small fields generated by 5 cm and 2.5 cm jaws positions, also comparing water phantom with solid water acquisitions. Discrepancies, found between the reference and pilot dataset, may be due to different equipment models, this will be evaluated by enrolling other pilot centers to the study. An analysis including all other italian departments will be taken on for smaller fields (1 cm jaw’s ) especially in order to establish a GAF reference dataset. Eventually, correction factors for the detector (here investigated and not present in TRS 483 protocol), could be calculated.

PO-1764 Implementation of SunCHECK Patient for systematic selection of gamma metrices in patient specific QA

T. Hehne 1 , P. Rosenthal 1 , A.A. Schönfeld 2 , N. Chofor 3

1 Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Klinik für Radioonkologie und Strahlentherapie, Berlin, Germany; 2 Sun Nuclear, A Mirion Medical Company, Research & Development, Melbourne, USA; 3 Sun Nuclear, A Mirion Medical Company, Research & Development , Melbourne, USA Purpose or Objective As a vital part of setting up our patient-specific QA (PSQA) program, we systematically investigated suitable gamma criteria for detecting clinically relevant errors. This work summarizes the investigations and clinical implementation of the SunCHECK Patient platform for the quality assurance (QA) of EPID in-vivo dosimetry (EIVD) at our institution. We evaluated error detectability for pre-clinical tests on a cylindrical cortical bone-surrogate and an anthropomorphic phantom. Results were further used to evaluate clinical patient head-and-neck (H&N) deliveries in an aim to establish gamma metric combinations for routine use. Materials and Methods We evaluated a conventional 3D open-field delivery, a dynamic IMRT and two VMAT plans, one with a 180° and the other a 360° arc. In all evaluations, gamma analysis was performed in PerFRACTION using a 10 % low dose threshold for various distance-to-agreement (DTA) and dose difference (DD) combinations. During delivery, the cylindrical bone surrogate was suspended within a water-filled tank, whereas the anthropomorphic Alderson phantom was placed on the treatment couch beneath a VARIAN Clinac. EPID acquisition was done both for the original plan and modified plans with investigations primarily focusing on errors with lateral and longitudinal shifts to mimic patient positional uncertainties. Obtained gamma metrices were then implemented for daily EIVD for our clinical cases. Results Analysis was done for a dose plane perpendicular to the normal beam incidence. The cortical bone tests did not show significantly representative results, due to the homogeneous nature and symmetry of the test object. Results from the Alderson phantom were more clinically relevant, and are shown here in the heat maps for the 3D and IMRT plans. Error detectability for the VMAT plans were more difficult, given the rigid nature of the phantom and the lack of effects from physiological changes.