Dosimetric uncertainness in verification of intensity modulated photon beams

doctoral thesis

• Title: Dozimetrijske nesigurnosti pri verifikaciji fotonskih snopova linearnog akceleratora modulirane jakosti
• Author: Slaven Jurković
• Mentor: Dario Faj (mentor)
• Committee member: Mladen Vrtar (predsjednik povjerenstva)
• Committee member: Jasminka Brnjas Kranjević (član povjerenstva)
• Committee member: Dario Faj (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2010-11-12, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53; NATURAL SCIENCES; Physics

Abstract

U disertaciji je opisana metoda za izračun oblika modulatora jakosti snopa linearnog akceleratora Osobitost metode je to što kod snopova s izrazito nehomogenim poprečnim presjecima, raspršeno zračenje uzima u obzir na egzaktniji način nego što je to bilo činjeno ranije. Metoda je primjenjiva u većini kliničkih situacija, a njena verifikacija je napravljena dozimetrijom ionizacijskim komorama i radiografskim filmom u različitim fantomima. Pri tome je na temelju mjerenja ionizacijskim komorama procjenjivan oblik kompenzatora, a radiografskim filmom su mjerene dvo-dimenzionalne raspodjele doze. Poznato je da je dozimetrija fotonskih snopova linearnog akceleratora modulirane jakosti, zbog nehomogene raspodjele doze, vrlo složena. Posebno stoga što se modulacijom jakosti snopa mijenja i energijski spektar snopa. Zbog toga su ispitane mogućnost korištenja i točnost različitih tipova detektora za mjerenje doznih distribucija snopova fotona. Korištene su ionizacijske komore malog volumena, poluvodički detektori različitih volumena, detektor od amorfnog silicija i radiografski film. Izmjerene raspodjele doze su uspoređivane međusobno, kao i sa raspodjelama dobivenim pomoću Monte Carlo simulacije transporta čestica. Na temelju toga predložena je najtočnija metoda za verifikaciju raspodjele doze u fotonskim snopovima linearnog akceleratora modulirane jakosti.

Abstract (english)

The doctoral thesis presents method for the calculation of the compensators’ shape to modulate linear accelerators’ beams. Characteristic of the method is more strict calculation of the scattered radiation in beams with an inhomogeneous cross-section than it was before. Method could be applied in various clinical situations. It's dosimetric verification was made in phantoms, measuring dose distributions using ionization chambers as well as radiographic film. Therefore, ionization chambers were used for the evaluation of modulator shape and film was used for the evaluation of two-dimensional dose distributions. It is well known that dosimetry of the intensity modulated photon beams is rather complicated regarding inhomogeneity of the dose ditribution. The main reason for that is the beam modulator which changes spectral distribution of the beam. Possibility of use different types of detectors for the measurements of dose distributions in modulated photon beams and their accuracy were examined. Small volume ionization chambers, different diodes and amorphus silicon detector and radigraphic film were used. Measured dose distributions were compared between each other as well as with distributions simulated using Monte Carlo particle transport algorithm. In this way the most accurate method for the verification of modulate photon beams is suggested.

• Keywords: modulacija intenziteta; kompenzatori; dozimetrija; Monte Carlo simulacija
• Keywords (english): intensity modulation; compenstators; dosimetry; Monte Carlo simulation
• Language: croatian
• URN:NBN: urn:nbn:hr:217:429440
• Study programme: Title: Fizika; Study programme type: sveučilišni; Study level: poslijediplomski doktorski; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika (doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika)
• Type of resource: Text
• Extent: 87 str.
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-08-24 07:10:35