ESTRO 2021 Abstract Book

S1352

ESTRO 2021

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Conclusion The first version of FilmQADog proved to be a useful, reliable and easy-to-use software for radiochromic film analysis allowing accurate and reproducible radiation therapy plan verification, thus facilitating accessibility to film-QA routine. The actual version was tested using Eclipse TPS, but current work focuses to develop the interface to other TPSs. It is hoped that this tool contributes to widely extend the use film dosimetry, especially in developing countries, where it can be one of the best alternatives for making radiation treatments secure. PO-1631 Validation of daily quality assurance of output, flatness and symmetry of an MR linear accelerator H.L. Riis 1,2 , A. Fietje 3 , K.H. Engstrøm 1 , U. Bernchou 4,5 , C. Brink 1,5 , V.N. Hansen 1 , A.S. Bertelsen 4 1 Odense University Hospital, Department of Oncology, Odense, Denmark; 2 University of Southern Denmark (SDU), Department of Clinical Research, Odense, Denmark; 3 Elekta Instrument AB, Service, Stockholm, Sweden; 4 Odense University Hospital, Department of Oncology, Odense , Denmark; 5 University of Southern Denmark (SDU), Department of Clinical Research, Odense , Denmark Purpose or Objective Daily quality assurance (QA) of the radiation beam on linear accelerators (linacs) used for radiotherapy is important for ensuring a high quality of treatment delivery to the patient at all times. Frequently QA has to be reliable, simple and fast to carry out. Linac build-in systems such as the MV imaging controller (MVIC) of the Elekta Unity MR linac has the advantages of easy to use and with no risk of collision during usage. This project was initiated by an abrupt change in the MVIC image analyses, Fig. 1, after two years of daily QA on an Elekta Unity using the MVIC. The abrupt change occurred around day 35 shown in the Fig. 1 after Elekta adjusted slightly the microwave energy by reducing the Charging Capacitive Power Supply (CCPS) value from 1200 to 1195 V. The CCPS parameter sets the energy of the microwaves. The aim of this work was to investigate the reliability of daily QA using the MVIC and how to interpret observed changes.

Materials and Methods A PTW 1D water phantom with two PTW Farmer chambers type T30006 located in a water phantom on the beam axis at depth 10 and 20 cm. The detector at depth 10 cm was located at the isocentre of the linac. An electrical pulse counter was connected to the linac. The gantry was at 90 degree, the field size was 22×10 cm,