ESTRO 2022 - Abstract Book

S1368

Abstract book

ESTRO 2022

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Conclusion In this study, linear regression analysis was used to predict the TrueBeam output drift over time and a unique factor identifying the rate of increase was found. Therefore, MPC with daily output measurements is a reliable tool in predicting TrueBeam output behavior and helping physicists to find the right timing for preventive beams calibration throughout the year. Further investigation is needed to eventually include in the analysis other factors affecting the output such as seasonal fluctuations and environmental factors.

PO-1587 HyperArcTM dosimetric validation for multiple targets using ionization chamber and polymer gel

L. zirone 1 , E. Bonanno 2 , G. Borzì 2 , N. Cavalli 2 , M. Pace 1 , G. Stella 2,1 , A. Girlando 3 , A.M. Gueli 4 , C. Marino 2,1

1 University of Catania, School of Medical Physics, Catania, Italy; 2 Humanitas - Istituto Clinico Catanese, Medical Physics, Catania, Italy; 3 Huminitas - Istituto Clinico Catanese, Radiotherapy, Catania, Italy; 4 University of Catania, Medical Physics, Catania, Italy Purpose or Objective Multiple brain metastases stereotactic radiosurgery (SRS) treatments with single isocenter approach are increasingly used in many radiotherapy departments. Because of the complexity of such techniques, it is recommended to perform end-to- end tests, before their introduction into the clinical routine, to evaluate the overall dosimetric and geometric uncertainties on the treatment planning and delivery system. In this work, we report the results of end-to-end tests for five HyperArc TM treatment plans using an ionization chamber (IC) and polymer gel. Materials and Methods Five SRS treatments with single and multiple brain metastases were planned using HyperArc TM technique with a prescription dose of 15-22 Gy and 6-9 Gy respectively for IC and polymer gel. The SRS plans were calculated using AcurosXB 15.6.06 algorithm on Eclipse v.15.6 Treatment Planning System (Varian Medical Systems), 6 MV Flattening Filter Free (FFF) mode, maximum dose-rate of 1400 UM/min, mono-isocenter technique and 3-4 non-coplanar arcs on a TrueBeam machine (Varian Medical Systems) with High Definition 120 MLC at Humanitas Istituto Clinico Catanese. The end-to-end tests were performed using a 3D-printed anthropomorphic head phantom. Point dose measurements were performed placing a CC04 ion chamber (IBA dosimetry) in the center of each target volume; a total of 15 plans was delivered. 2D and 3D dose distributions were evaluated for each target using polymer gel (RTsafe). 24h after irradiation, the phantom filled of gels was read by Philips dStream 1,5T Magnetic Resonance Imaging (MRI). The dose distributions measured by the polymer gels were compared to the dose distribution calculated by the treatment planning system using gamma evaluation by different criteria (5%2mm, 3%2mm). Results A mean point dose difference of 0.23% [min 0.01% - max 2.81%] was found using IC. For each target volume the results obtained in terms of ɣ index passing rate show an agreement > 95% with 5%2mm and 3%2mm criteria for both 2D and 3D distributions. Conclusion The HyperArc TM dosimetric validation has allowed the introduction of this technique in the clinical routine of Humanitas Istituto Clinico Catanese. Further investigations will regard the use of a 3D printer for customized anthropomorphic phantoms.