Mjerenja perifernih doza za različite kolimatore gama noža

master's thesis

• Title (english): Measurements of peripheral organ doses for different secondary collimators of gamma knife
• Author: Paula Tomić
• Mentor: Marija Majer (mentor)
• Mentor: Nikola Poljak (mentor)
• Committee member: Nikola Poljak (predsjednik povjerenstva)
• Committee member: Marija Majer (član povjerenstva)
• Committee member: Tomislav Marketin (član povjerenstva)
• Committee member: Matko Milin (član povjerenstva)
• Committee member: Matko Glunčić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2016-11-15, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

U Leksellovom gama nožu se za oblikovanje promjera fotonskih snopova koriste primarni statički i sekundarni izmjenjivi kolimatori. U ovom diplomskom radu proučena je ovisnost perifernih doza o sekundarnom kolimatoru te je na jednostavnom primjeru radiokirurškog plana zračenja provjereno mogu li se dobiveni rezultati iskoristiti za procjenu perifernih doza u tretmanu gama nožem koji uključuje sva četiri sekundarna kolimatora. Mjerenja su provedena na antropomorfnom fantomu koji predstavlja desetogodišnje dijete, a za mjerenje doza su korišteni radiofotoluminescentni dozimetri koji su stavljeni u organe fantoma. Sekundarni kolimatori karakterizirani su promjerom otvora (4, 8, 14 i 18 mm) te izlaznim faktorom određenim od strane proizvođača gama noža. Za svaki od četiri sekundarna kolimatora napravljen je plan zračenja za isti ciljni volumen te su za svaki kolimator izmjerene periferne doze i izračunate doze u organima. Najveće periferne doze izmjerene su za 18 mm kolimator. Izborom kolimatora s manjim otvorima (14 mm i 8 mm) periferne doze su se smanjivale što je objašnjeno manjim curenjem zračenja. Za 4 mm kolimator nije nastavljen trend smanjivanja periferne doze. Prosječna periferna doza po organima za 4 mm kolimator usporediva je s vrijednosti dobivenom za najveći 18 mm kolimator što je objašnjeno značajno manjim izlaznim faktorom (te za istu dozu u ciljnom volumenu većim vremenom zračenja) za 4 mm kolimator nego za druge kolimatore. Za svaki organ izračunat je koeficijent kao omjer doze u organu i maksimalne doze u ciljnom volumenu. Pomoću tih koeficijenata, za svaki organ su izračunate periferne doze za plan zračenja u kojem se koriste sva četiri kolimatora, te su uspoređene s izmjerenim dozama. Slaganje izmjerenih i izračunatih doza je zadovoljavajuće.

Abstract (english)

The Leksell Gamma Knife radiation is collimated both by a fixed primary collimator system and a secondary replaceable collimator. The purpose of this diploma work was to study the dependence of the paediatric patient peripheral doses on the choice of the secondary collimator and for simple radiosurgery treatment plan verify whether the results obtained can be used to estimate peripheral doses if all four secondary collimators are used for gamma knife treatment. An anthropomorphic phantom representing a 10 year old child was used for measurements. Radiophotoluminescent dosimeters placed in the organs of the phantom were used for dose measurements. Secondary collimators are characterized with the diameter of their holes and output factor defined by the vendor. For each of the four secondary collimators, a treatment plan for the same target volume was made and for each collimator the peripheral doses were measured and organ doses were calculated. The highest peripheral doses were measured for a 18 mm collimator. By selecting collimators with smaller apertures (14 mm and 8 mm) the peripheral doses were decreased, which was explained by the smaller radiation leakage. The trend of reducing peripheral doses with the decrease of aperture size was not obtained for the 4 mm collimator. For the 4 mm collimator the average peripheral organ dose was comparable with value obtained for 18 mm collimator and that was explained with much smaller output factor (and the larger irradiation time for the same target dose) for the 4 mm collimator in comparison with other collimators. For each of the organs, a factor representing the ratio of the organ dose and the maximum target dose was calculated. Using these factors for a treatment plan that uses four collimators, the peripheral organ doses were calculated and compared to measured values. The comparison of measured and calculated doses was satisfactory.

• Keywords: Leksellov gama nož; dozimetrija
• Keywords (english): Leksell Gamma Knife; dosimetry
• Language: croatian
• URN:NBN: urn:nbn:hr:217:818507
• Study programme: Title: Physics; specializations in: Research; Course: Research; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra fizike (magistar/magistra fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-03-05 12:48:56