Dosimetric characterization of medical linear accelerator Photon and Electron beams for the treatment accuracy of cancer patients

In radiotherapy treatment planning process, quality assessment (QA) is indispensable for achieving accuracy and avoidance of treatment errors. In this perspective, present study focused on the Photon and Electron beams characterization of a medical linear accelerator (LINAC) to ascertain dosimetric QA in Absolute and Reference dosimetry. In this connection, the beam outputs were investigated in terms of Dmax and Dw,max (dose at depth dmax) in absolute dosimetry for Photon and Electron beams, respectively. In accordance with the measured Dmax and Dw,max parameters, Photon and Electron beam outputs were standardized to ensure standard output of 1 cGy/MU. In reference dosimetry, the parametric evaluation was performed for dosimetric QA in terms of percent depth dose (PDD), beam profile flatness and symmetry, output factors: Scp, Sc, Sp with varying field size (FS) ranging from 4´4 cm2 to 40´40 cm2 normalized at FS 10´10 cm2 for the 6 MV and 10 MV Photon beams. The measured PDDs at 10 cm depth (D10) were found to be 66.8% and 73.6% for 6 MV and 10 MV Photon beams, respectively, with significantly small deviation of 1% and 0.8% in comparison with an international PDD protocol of British Journal of Radiology-25 (BJR -25). In the case of Electron beams characterization, PDD was verified with 10´10 cm2 cone/applicator, beam profile flatness and symmetry were analyzed at the field sizes ranging from 6´6 cm2 to 25´25 cm2 normalized at 10´10 cm2 cone/applicator, and Electron cone ratios were investigated for a given cone/applicator relative to the 15´15 cm2 one for the 6, 9, 12, 15 MeV Electron energies. The PDDs of all the Electron beams revealed reasonable consistency with manufacturer’s estimations of 90%, 80%, and 50% PDDs at various depths of ionization.