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Linac Dynamic QA with An EPID

F San Miguel*, F Clemente-Gutierrez, P Chamorro Serrano, Hospital Central de la Defensa "Gomez Ulla", Madrid, MES

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
One of the main issues that a medical physicist could face, is that is impossible to find an ideal device for measuring all the different tests suggested in the guidelines. Another inconvenience is that there are no recommendations for dynamic QA (DMLC, VMAT). The aim of the work is to develop a dynamic QA program, using only the EPID. Besides the advantage of being mounted on the linac, it also has a high resolution.

Methods:
For this study it has been used the EPID mounted on an Elekta Synergy accelerator . The panel was calibrated in water for absolute dosimetry and tested against a farmer type ion chamber. This procedure allowed to replace the ion chamber in dosimetry tests. Dynamic tests were designed including positioning of the MLC using different delivery techniques, leaf speed and backup jaw speed, flatness and symmetry as a function of dose rate, etc. The files for controlling each component of the delivery were implemented using the iCom Customer Acceptance Test (iComCAT). Using the raw images exported from IviewGT (version 3.4) as input data, the analysis was made with a self-developed software.

Results:
Physical analysed data, like leaf and gantry speed, showed very small differences between the nominal values entered in the treatment planning system (TPS) and the values measured. Dosimetric results also showed good agreement between the static and dynamic deliveries.

Conclusion:
Although slight differences were observed, it does not seem to be clinically relevant since the same device is used to measure IMRT planar dose maps, with quite good agreement with the TPS (previously tested against other devices). Dynamic QA can be performed with only one measuring device, already mounted on the linac, and one software. This allows the user for a fast method that can be included in the routine procedures.

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