Naslov
EXPERIMENTAL DETERMINATION OF FIELD OUTPUT FACTORS AND DETECTOR SPECIFIC OUTPUT CORRECTION FACTORS IN SMALL FIELDS OF MEGAVOLTAGE RADIOTHERAPY BEAMS

Autori
Casar, Božidar

Vrsta, podvrsta i kategorija rada
Ocjenski radovi, doktorska disertacija

Fakultet
Prirodoslovno-matematički fakuletet

Mjesto
Zagreb

Datum
18.04

Godina
2019

Stranica
142

Mentor
Jurković, Slaven ; Jeraj, Robert

Ključne riječi
W1 scintillator, EBT3 films, diodes, ionization chambers, small fields, field output factors

Sažetak
The goal of this work was to determine field output factors, Ω𝑄𝑐𝑙𝑖𝑛, 𝑄𝑟𝑒𝑓 𝑓𝑐𝑙𝑖𝑛, 𝑓𝑟𝑒𝑓 , using EBT3 radiochromic films and W1 plastic scintillator as reference detectors on two different linear accelerators. Secondly, we aimed to provide a large and consistent set of data for detector specific output correction factors, 𝑘𝑄𝑐𝑙𝑖𝑛, 𝑄𝑟𝑒𝑓 𝑓𝑐𝑙𝑖𝑛, 𝑓𝑟𝑒𝑓 , for small static fields for seven solid state detectors and seven small ionization chambers. In the case of ionization chambers, 𝑘𝑄𝑐𝑙𝑖𝑛, 𝑄𝑟𝑒𝑓 𝑓𝑐𝑙𝑖𝑛, 𝑓𝑟𝑒𝑓 were determined in two orientations – parallel and perpendicular, to test the hypothesis, that 𝑘𝑄𝑐𝑙𝑖𝑛, 𝑄𝑟𝑒𝑓 𝑓𝑐𝑙𝑖𝑛, 𝑓𝑟𝑒𝑓 are lower and therefore advantageous for parallel orientation. Ω𝑄𝑐𝑙𝑖𝑛, 𝑄𝑟𝑒𝑓 𝑓𝑐𝑙𝑖𝑛, 𝑓𝑟𝑒𝑓 were determined for 6 and 10 MV photon beams with and without flattening filter and for nine fields ranging from 0.5 x 0.5 cm2 to 10 x 10 cm2 . Signal readings obtained with EBT3 radiochromic films and W1 plastic scintillator were fitted by an analytical function. 𝑘𝑄𝑐𝑙𝑖𝑛, 𝑄𝑟𝑒𝑓 𝑓𝑐𝑙𝑖𝑛, 𝑓𝑟𝑒𝑓 were determined empirically for 14 clinically used small detectors, under the same experimental conditions. It has been found that, for a given linear accelerator, Ω𝑄𝑐𝑙𝑖𝑛, 𝑄𝑟𝑒𝑓 𝑓𝑐𝑙𝑖𝑛, 𝑓𝑟𝑒𝑓 need to be determined for every combination of photon beam energy, filtration, and field size as the differences between them can be statistically significant (p < 0.05). Further, it has been demonstrated, that the parallel orientation of ionization chamber is advantageous over the perpendicular, which is an important contribution to the present international dosimetry protocol for small fields IAEA TRS-483. Use of two reference detectors for the determination of field output factors for small static fields in MV photon beams is a novel approach and has been justified in our thesis. Large set of 𝑘𝑄𝑐𝑙𝑖𝑛, 𝑄𝑟𝑒𝑓 𝑓𝑐𝑙𝑖𝑛, 𝑓𝑟𝑒𝑓 data for seven solid-state detectors and seven ionization chambers in four MV beams determined on two linear accelerators by a single group of researchers can be considered a valuable supplement to the literature and the IAEA TRS-483 dataset. Recommendation on the orientation of ionization chambers is the last significant outcome of our work.

Izvorni jezik
Engleski

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