Dozimetrijska provjera konvolucijskog algoritma za izračun apsorbirane doze u radiokirurgiji mozga Leksellovim gama nožem

master's thesis

• Title (english): Dosimetric verification of convolution algorithm for absorbed dose calculation in Leksell Gamma Knife brain radiosurgery
• Author: Gabriela Jazvac
• Mentor: Hrvoje Hršak (mentor)
• Mentor: Tomislav Bokulić (komentor)
• Committee member: Tomislav Bokulić (predsjednik povjerenstva)
• Committee member: Hrvoje Hršak (član povjerenstva)
• Committee member: Mihael Makek (član povjerenstva)
• Committee member: Damir Bosnar (član povjerenstva)
• Committee member: Ivica Friščić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2024-02-19, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

U planiranju radiokirurgije mozga Leksellovim gama nožem koristi se računalni sustav za izračun i optimizaciju apsorbirane doze. Najčešće korišteni algoritam u sustavu za planiranje terapije Leksell GammaPlan (LGP, Elekta AB, Stockholm, Švedska) je TMR 10 (Elekta AB, Stockholm, Švedska), temeljen na omjeru tkivo-maksimum. On pretpostavlja da je gustoća tkiva ekvivalentna gustoći vode te da su sastav i gustoća svih tkiva homogeni. U neposrednoj blizini heterogenih struktura, predana apsorbirana doza i doza koju je izračunao TMR 10 algoritam mogu se znatno razlikovati. Uz TMR 10 algoritam dostupan je i konvolucijski algoritam. On konvoluira funkcije koje opisuju kako se energija prenosi iz primarnog fotonskog snopa na sekundarne elektrone sa funkcijama koje opisuju kako se ta energija dalje prenosi u tkivo. Time se uzimaju u obzir razlike medu tkivima. U ovom radu proveli smo dozimetrijsku provjeru točnosti konvolucijskog algoritma za jednostavne jednoizocentričke raspodjele doze Leksellovog gama noža, uz pretpostavku da se njime točnije računa apsorbirana doza u odnosu na TMR 10 algoritam. Za provjeru su korišteni radiokromski film GAFChromic EBT3 (Ashland Advanced Materials, Bridgewater, New Jersey, SAD), ionizacijske komore Semiflex TM31010 i PinPoint3D TM31022 (PTW, Freiburg, Njemačka) i silicijski detektor Diode E (PTW, Freiburg, Njemačka). Rezultati ovog rada ne podržavaju pretpostavku da konvolucijski algoritam točnije računa apsorbiranu dozu od TMR 10 algoritma za ciljne volumene u središtu mozga. TMR 10 algoritam daje rezultate unutar 2.1% od eksperimentalnih vrijednosti, čime daje točnije rezultate od konvolucijskog algoritma za većinu mjernih točaka, čija su odstupanja do 3.1%. Konvolucijski algoritam sustavno podcjenjuje apsorbiranu dozu. Sve računalno određene raspodjele doze i izlazni faktori su u odličnom slaganju s referentnim vrijednostima.

Abstract (english)

In the planning process of Leksell Gamma Knife brain radiosurgery a treatment planning system is used for the calculation and optimization of the absorbed dose. The most commonly used algorithm in Leksell Gamma Plan treatment planning (LGP, Elekta AB, Stockholm, Sweden) system is the TMR 10 algorithm (Elekta AB, Stockholm, Sweden), based on the tissue maximum ratio. It assumes tissue-water equivalency along with the homogeneity of tissue composition and density. Near heterogeneous structures, the dose delivered to the target volume and the dose calculated by the TMR 10 Algorithm can differ significantly. The convolution algorithm is available alongside the TMR 10 algorithm. It convolves functions describing the energy transfer between the primary photon beam and the secondary electrons with functions describing how that energy is further distributed in tissue. That way it accounts for the differences between tissues. This study aimed to verify the convolution algorithm’s accuracy for simple mono-isocentric dose distributions of Leksell Gamma Knife under the assumption that it might perform more accurately than the TMR 10 algorithm in the absorbed dose calculation. The detectors used were the GAFChromic EBT3 radiochromic film (Ashland Advanced Materials, Bridgewater, New Jersey, USA), the Semiflex TM31010 and the PinPoint3D TM31022 cylindrical ionization chambers (PTW, Freiburg, Germany) and the Diode E silicon detector (PTW, Freiburg, Germany). The results of this study do not support the hypothesis that the convolution algorithm performs better than the TMR 10 algorithm in calculation of the absorbed dose for the mid-brain locations of interest. The TMR 10 algorithm performs within 2.1% or less relative to the experimental values, yielding more accurate results than the convolution algorithm for most measurement points, which differ up to 3.1%. The convolution algorithm systematically underestimated the absorbed dose. All output factors and dose profiles calculated with both algorithms were in excellent agreement with reference values.

• Keywords: Leksellov gama nož; TMR 10 algoritam; konvolucijski algoritam
• Keywords (english): Leksell Gamma Knife; convolution algorithm; TMR 10 algorithm
• Language: croatian
• URN:NBN: urn:nbn:hr:217:343321
• Study programme: Title: The University Integrated Undergraduate and Graduate Programme in Physics; Research Physics; specializations in: Research Physics; Course: Research Physics; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: sveučilišni magistar fizike (sveučilišni magistar fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2024-04-05 12:22:56