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Comparison of Photoneutron Dose Equivalent Measurements for Two Different Medical Clinac

H Khilafath1*, G Bharanidharan2, G Singaravelu3, P Mahadevan4, J Vellingiri5, A Prakash Rao6, D Mohapatra7, N Sekar8, T Palraj9, (1) Anna University, ,,(2) Anna University, Chennai, ,IN, (3) ,,,(4) ,,,(5) ,,,(6) ,,,(7) Breactor And Radiological Safety Section, Safety Research Institute, Atomic, ,,(8) ,,,(9) ,


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

Room: AAPM ePoster Library


Cancer remains as one of the greatest threats to human health and poses clinical challenges despite fast development in the field of diagnostics and therapy. X-ray photons interacts with the higher atomic number materials present in the linac head which produce secondary neutron field due to photonuclear giant dipole resonances (GDR). The present study investigatesthe effect of flattening filter on photoneutron production for10MV photon beam produced from a Medical Linac.


The commercially available ClinacVarian TrueBeamTM(VTB) and Elekta VersaHD (EV) were utilized for the study. The Photoneutron dose equivalent (PNDE) was measured using a bubble detector based personal neutron dosimeter (BD-PND). The measured neutron dose equivalent (NDE) expressed in terms of bubbles per microsievert, and the PNDE has derived from the measured values of NDE for a field size of 5×5 cm2. The PNDE were estimated at a distance of 25, 50 and 100cm along the patient plane from field edge.


The measured PNDE for VTB were 89.3, 82.3 and 67.7 µSv/Gy at a distance of 25, 50, 100 cm for FF beam, and similarly for same distances the PNDE estimated for FFF beam were 76.8, 70.1 and 57.8 µSv/Gy, respectively.In case of EV, the measured PNDE was found to be 68.3, 60.9 and 50.1µSv/Gy at distance of 25, 50, 100 cm for FF beam and 61.6, 54.0 and 45.6 µSv/Gy for FFF beam, respectively.


The result infers that the ambient PNDE production is higher for the flattening filter when compared with the flattening filter free mode in both the medical Linac’s. Even though, the PNDE is relatively higher for Varian TruebeamTM when compared with an Elekta VersaHD Linac and the dose variation is not significant.


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