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Analytical Study of Flatness and Symmetry of Electron Beam with 2D Array Detectors

Abstract

Pankaj Pathak, Praveen Kumar Mishra, Manisha Singh and Pankaj Kumar Mishra

Aims: The main aim of our study is to analyse Electron Beam Profiles like Flatness, Symmetry with 2D Array Detectors. The 2D Array can be used as an alternative device to measure the Electron beam profiles.

Introduction: Flatness and symmetry of a radiation beam: The flatness of the beam is defined by the following formula: Flatness (%) = Dmax/Dmin × 100% (1) Where Dmax and Dmin are the maximum and minimum doses respectively within the area. Radiation field symmetry is defined as the maximum ratio of doses at two symmetric points relative to the central axis of the field. Symmetry (%) = [D(x, y)]/[D (-x,-y)] × 100% (2)

Methods and Material: The beam symmetry is easily defined and is not very dependent on the depth of measurement. However, the flatness of the beam depends on the size and shape of the measurement phantom. However, 3% is sufficient measurement accuracy for a quick check. We measured the electron profiles of energies (4 MeV, 6 MeV, 8 MeV, 10 MeV, 12 MeV, 15 MeV and 18 MeV) from Elekta Synergy Linear accelerator for different electron applicators (6 × 6, 10 × 10, 14 × 14 and 20 × 20) at their depth of maximum dose (dm) respectively and Source-Surface-Distance (SSD) of 100 cm using PTW 729 2D array detectors.

Results: We analyzed the variations in Flatness and Symmetry of electron energies obtained from 729 2D Array Detector and compared with the standard values obtained from the Radiation Field Analyzer (RFA) during Commissioning.

Conclusions: We found that there is no significant variation in Flatness and symmetry obtained from the 729 2D Array detector as compared to the standard Flatness and symmetry obtained from the RFA .Thus we conclude that 729 2 D Array detector can be used for the routine measurement of electron beam profiles.