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The purpose of this work was to evaluate computed tomography simulators used in radio-therapy treatment planning in Serbia, Croatia, and Bosnia and Herzegovina. A survey of quality assurance programmes of 24 computed tomography simulators in 16 facilities was conducted. A dedicated CT-to-ED phantom was scanned at 120 kV and 140 kV, to obtain CT-to-ED conversion curves as well as CTDIvol. Thoracal phantoms were scanned in the standard and extended field of view to evaluate the dosimetric effect on treatment planning and delivery. The mean age of the measured scanners was 5.5 years. The mean water HU value was –6.5 (all scanners, all voltages) and air HU value was –997. Extended field of view computed tomography data differ from the standard field of view and differences between conversion curves have significant dosimetric impact. The CTDI data showed a large range of values between centers. Better quality assurance of computed tomography simulators in all countries is recommended. The CT-to-ED curve could be used as default at one voltage and per manufacturer. Extended field of view imaging can be used, but treatment planning should be avoided in the regions out of the standard field of view.

Poznavanje spektra x-zračenja kao i drugih osobina je od izuzetnog značaja kako za planiranje radijacione terapije tako i sa aspekta zaštite pacijenta i osoblja. Takođe, poznavanje svojstava neutrona nastalih u interakciji fotona sa materijalima oko akceleratora, je od izuzetnog značaja sa dozimetrijskog aspekta. Poslednjih godina sve se više upotrebljavaju linearni akceleratori bez homogenizacionog filtera tzv. FFF (Flatteninig Filter Free), a kako su karakteristike snopa u toma načinu rada akceleratora još uvek nedovoljno ispitane, njima smo posvetili posebnu pažnju. Urađena su i detaljna dozimetrijska merenja fotona kako u radu sa homogenizacionim filterom (FF) tako i bez njega (FFF), kao i dozimetrijsko merenje neutrona. Direktno merenje samog spektra nekim od detektora (NaI ili HPGe) nije moguće zbog visokih intenziteta stoga smo u radu koristili indirektne metode i to aktivacionu analizu i atenuacionu analizu. Urađena su detaljna dozimetrijska merenja ekvivalentne doze neutrona u terapijskoj sobi sa dva zaokreta hodnika i na osnovu rezultata predložena je korekcija metode za izračunavanje neutronske doze na ulaznim vratima. Fotoaktivacionimmerenjima, gde su se u oba načina rada terapijskog akceleratora pratile aktivnosti izomera 115m In, ustanovljeno je da se kod dva tipa akceleratora (Elekta Versa HD, Varian TrueBeam) oblik spektra u visokoenergetskom delu znatno razlikuje, kao i da postoji razlika u obliku spektra na ivici polja i u njegovoj sredini. Atenuacionom analizom na osnovu standardnog metoda rekonstrukcije fotonskog spektra putem Laplasovih transforma, dobijene su izvesne razlike u oblicima spektara za dva režima rada. Takođe, rekonstrukcijom spektra putem odabira parametara korekcine funkcije koja bi teorijski oblik spektra (Šifova funkcija) trebao da prevede u realan spektar za oba režima rada dobijene su izvesne razlike u oblicima spektra. Dozimetrijska merenja fotonske doze na ulaznim vratima terapijske sobe sa jednim zaokretom, s, Knoweledge of the x-ray spectrum as well as other characteristics of the beam is of great importance both for the planning of radiotherapy as well as for the protection of patients and staff. Also, the knowledge of the neutron properties generated in the interaction of photons with materials around the accelerator is of great importance from the dosimetric aspect. In recent years, linear accelerators are increasingly used without a flattening filter, so-called FFF (Flatteninig Filter Free), and as the characteristics of the beam in this mode of operation of the accelerator are still insufficiently investigated, we paid special attention to them. Detailed dosimetric measurements of photons were performed both with (FFF) and without the flattening filter (FF), as well as the dosimetric measurement of the neutron. Direct measurement of the spectrum itself by detectors (NaI or HPGe) is not possible due to high intensities, therefore, we used indirect methods in this work, both activation analysis and attenuation analysis. Detailed dosimetric measurements of the neutron equivalent dose in the therapeutic room with two band maze were made and based on the results, correction of the method for calculating the neutron dose at the entrance door was proposed. It was found by photoactivation measurements, where the activities of the isomer 115mIn were investigated, that in the two types of accelerators (Elekta Versa HD, Varian TrueBeam) the spectrum shape in the high-energy part is significantly different, and that there is a spectrum difference in the edge of the field and in the middle of the field. Attenuation analysis, based on the standard method of reconstructing the photon spectrum through Laplace transforms, showed some differences in the spectra of the two working modes of accelerators. Also, by reconstructing the spectrum by correction function that should transform the theoretical spectrum form (the Schiff function) into a real spectrum for