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Investigating the Electronic Portal Imaging Device for Small Radiation Field Measurements

J Koilpillai

KJ Maria Das1*, A Agarwal2 , N Nikhil Rastogi2 , SA Yoganathan1 , D Udayakumar1 , S Kumar1 , (1) Sanjay Gandhi PG Inst Med Scienes, Lucknow,Uttar Pradeh, INDIA (2) IFTM University, Moradabad, Uttar Pradesh, INDIA


SU-I-GPD-T-257 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: With the advent of state of art treatment technologies the use of small fields has been increased and dosimetry in small fields is highly challenging. In this study the potential use of Varian electronic portal imaging device (EPID) for small field measurements was explored for 6 and 15 MV photon beams.

Methods: The output factors and profiles were measured for a range of jaw collimated square field sizes starting from 0.8x0.8 cm2 to 10x10 cm2 using EPID. For evaluation purpose, reference data was also acquired using Exradin A16 micro ionization chamber (0.007cc) for output factors and stereotactic field diode for profile measurements in a radiation field analyzer.

Results: The output factors of EPID were in agreement with the reference data for field sizes down to 2x2 cm2 and for 6 MV the difference in output factors was +2.06% for 2x2 cm2 and +1.56% for 15 MV. For the lowest field size studied (0.8x0.8 cm2) the differences were maximum; +16% for 6 MV and +23% for 15 MV photon beam. EPID profiles of both energies were closely matching with reference profiles for field sizes down to 2x2 cm2 however; penumbra and measured field size of EPID profiles were slightly lower compared to its counterpart

Conclusion: EPID is a viable option for profile and output factor measurements for field sizes down to 2x2 cm2 in absence of appropriate small field dosimeters.

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