Utjecaj pogrešaka pozicioniranja na izračun doze kod adjuvantnog zračenja

master's thesis

• Title (english): Influence of positioning errors on dose calculation for adjuvant radiation
• Author: Nikolina Mišak
• Mentor: Vedran Rajevac (mentor)
• Mentor: Davor Horvatić (mentor)
• Committee member: Davor Horvatić (predsjednik povjerenstva)
• Committee member: Vedran Rajevac (član povjerenstva)
• Committee member: Gorjana Jerbić-Zorc (član povjerenstva)
• Committee member: Mihael Makek (član povjerenstva)
• Committee member: Ana Sušac (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2014-07-16, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

Izrada radioterapijskog plana zračenja zahtijeva detaljno poznavanje fizikalnih procesa prijenosa energije ionizirajućeg zračenja na tvari, izbor algoritama koji omogućuju dovoljno točan i prihvatljivo brz proračun. U diplomskom radu se proučava utjecaj pogreške pozicioniranja na izračun doze kod adjuvantnog zračenja lijeve dojke. Usporedba kvalitete plana zračenja je načinjena usporedbom dozno volumnih histograma (DVH). Volumen pacijenta, odnosno geometrija u kojoj se radi proračun, je zadan u obliku CT slojeva debljine 2 mm. Onkolog na slojevima obilježi konture ciljnih volumena, rizičnih organa te zadaje uvjete u obliku frakcionirane terapijske doze na ciljne volumene (PTV, CTV) te dozna ograničenja. Cijeli volumen je podijeljen na prostorne elemente (voxele), kockice brida 2 mm. Za svaki voksel zna se kolika je njena prosječna elektronska gustoća i kakvom tkivu ili u planu obilježenom volumenu pripada. Fizičar izrađuje plan zračenja, usmjeravajući odabrane terapijske snopove tako da se u terapijskom volumenu postigne zadana homogena apsorbirana doza, a u drugim tkivima unutar dozvoljenih granica. Primijenjen je algoritam multigrid superpozicije. U proračunu se uvažavaju različite elektronske gustoće pojedinih volumnih elemenata. Međutim, u procesu terapije javlja se još jedna nesigurnost – pogreška koja se javlja kod postavljanja pacijenta za zračenje (set up pogreška) koja može biti sistematska ili slučajna, a može iznositi od nekoliko mm do nekoliko cm u svakom od smjerova koordinatnih osi. Diplomski rad se bavi utjecajem takve pogreške na raspodjelu doze. Pogreška namještanja je simulirana pomakom izocentra u tri dimenzija za po 2.5 mm u intervalu od -30 mm do +30 mm. Na taj način je generirano 72 plana zračenja, te se postupak ponavlja za 5 pacijentica. Za izdvajanje i obradu podataka potrebnih za usporedbu planova korištene su pogodnosti programskog jezika Python. U metodičkom dijelu razrađena je priprema za sat na temu fotoelektričnog efekta koji se obrađuje u srednjoj školi.

Abstract (english)

Developing radiotherapy radiation plan requires detailed knowledge of the physical process of ionizing radiation energy transfer on matter, variety of algorithms that allow sufficiently accurate and acceptable fast calculation. Influence of positioning errors on dose calculation for adjuvant radiation of left breast is studied in this graduation work. Comparison of the quality of the plan was made by comparing the radiation dose-volume histograms (DVH). The volume of the patient, or the geometry in which calculation are made, is given in the form of CT slices thickness of 2 mm. Oncologist on slices marks the contours of the target volume, organs at risk and sets the conditions in the form of fractionated therapeutic dose to the target volume (PTV, CTV) and dose restrictions. The whole volume is divided into spatial elements (voxels), cubes with edge of 2 mm. Average electron density for each cube is known and to which tissue or plan marked volume it belongs. Physicist makes a plan of radiation, directing selected therapeutic beams so that the therapeutic volume reaches default homogeneous absorbed dose and other tissues within the allowable limits. Multigrid superposition algorithm it is applied. The calculation will take into account the different electron density of individual volume elements. However, in the process of therapy, there is another uncertainty - an error that occurs during patient positioning for radiation (set-up error), which can be systematic or random and can be in range from a few mm to a few cm in all directions of coordinate axis. This work analyze the impact of such errors on dose distribution. Setting error is simulated by moving the isocenter in the three dimensions by 2.5 mm at an interval of -30 mm to +30 mm. That generated 72 radiation plans and the process was repeated for 5 patients. To extract and process the data needed to compare radiation plans, programming language Python has been used. Preparations for a class on the subject of the photoelectric effect, which is taught in high school, is developed in the methodological part.

• Keywords: zračenje; algoritmi; radioterapija
• Keywords (english): radiation; algorithms; radiotherapy
• Language: croatian
• URN:NBN: urn:nbn:hr:217:277306
• Study programme: Title: Physics and Computer Science; specializations in: Education; Course: Education; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra fizike i informatike (magistar/magistra fizike i informatike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Access restricted to students and staff of home institution
• Created on: 2017-06-16 10:26:53