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  • Output correction factors for small static fields in megavoltage photon beams for seven ionization chambers in two orientations - perpendicular and parallel
    Casar, Božidar ...
    The goal of the present work was to provide a large set of detector-specific output correc-tion factors for seven small volume ionization chambers on two linear accelerators in four megavolt-age ... photon beams utilizing perpendicular and parallel orientation of ionization chambers in the beamfor nominal field sizes ranging from 0.5 cm290.5 cm2to 10 cm2910 cm2. The present study isthe second part of an extensive research conducted by our group.Methods:Output correction factorskfclin;frefQclin;Qrefwere experimentally determined on two linacs, ElektaVersa HD and Varian TrueBeam for 6 and 10 MV beams with and without flattening filter for ninesquare fields ranging from 0.5 cm290.5 cm2to 10 cm2910 cm2, for seven mini and micro ion-ization chambers, IBA CC04, IBA Razor, PTW 31016 3D PinPoint, PTW 31021 3D Semiflex, PTW31022 3D PinPoint, PTW 31023 PinPoint, and SI Exradin A16. An Exradin W1 plastic scintillatorand EBT3 radiochromic films were used as the reference detectors.Results:For all ionization chambers, values of output correction factorskfclin;frefQclin;Qrefwere lower for par-allel orientation compared to those obtained in the perpendicular orientation. Five ionization cham-bers from our study set, IBA Razor, PTW 31016 3D PinPoint, PTW 31022 3D PinPoint, PTW 31023PinPoint, and SI Exradin A16, fulfill the requirement recommended in the TRS-483 Code of Prac-tice, that is, 0:95\kfclin;frefQclin;Qref\1:05, down to the field size 0.8 cm290.8 cm2, when they are posi-tioned in parallel orientation; two of the ionization chambers, IBA Razor and PTW 31023 PinPoint,satisfy this condition down to the field size of 0.5 cm290.5 cm2.Conclusions:The present paper provides experimental results of detector-specific output correctionfactors for seven small volume ionization chambers. Output correction factors were determined in 6and 10 MV photon beams with and without flattening filter down to the square field size of0.5 cm290.5 cm2for two orientations of ionization chambers%perpendicular and parallel. Ourmain finding is that output correction factors are smaller if they are determined in a parallel orienta-tion compared to those obtained in a perpendicular orientation for all ionization chambers regardlessof the photon beam energy, filtration, or linear accelerator being used. Based on our findings, we rec-ommend using ionization chambers in parallel orientation, to minimize corrections in the experimen-tal determination of field output factors. Latter holds even for field sizes below 1.0 cm291.0 cm2,whenever necessary corrections remain within 5%, which was the case for several ionization cham-bers from our set.TRS-483 recommended perpendicular orientation of ionization chambers for the determination offield output factors. The present study presents results for both perpendicular and parallel orientationof ionization chambers. When validated by other researchers, the present results for parallel orienta-tion can be considered as a complementary dataset to those given in TRS-483.
    Vir: Medical physics. - ISSN 0094-2405 (Vol. 47, no. 1, Jan. 2020, str. 242-259)
    Vrsta gradiva - članek, sestavni del
    Leto - 2020
    Jezik - angleški
    COBISS.SI-ID - 3447931
    DOI

vir: Medical physics. - ISSN 0094-2405 (Vol. 47, no. 1, Jan. 2020, str. 242-259)

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