Ocena nastavitvenih napak pri obsevanju bolnikov z rakom glave in vratu: pomen individualnih podlag za glavo : magistrsko delo

Androjna, Sabina (author), Strojan, Primož (mentor), Žager Marciuš, Valerija (co-mentor)

Uvod: Sledenje interfrakcijskih premikov ima v radioterapiji glave in vratu še posebno velik pomen, ker lahko že majhni premiki povzročijo predoziranost kritičnih organov in poddoziranost tarče. Glavno vlogo pri zmanjševanju tako nastavitvenih napak, kot tudi varnostnih robov ima zanesljiva in ponovljiva imobilizacija, ki jo lahko zagotovimo tudi z uporabo individualnih podlag za glavo in vrat. Namen: Namen raziskave je ovrednotiti natančnost obsevanja bolnikov z rakom glave in vratu ob uporabi standardnih in individualnih podlag za pod glavo in vrat ter primerjati izmerjene premike portalnih slik s pomočjo analiziranih sistematičnih in naključnih napak ter izračunanega varnostnega roba po van Herkovi formuli. Metode dela: V raziskavo je bilo vključenih 120 bolnikov z rakom glave in vratu, obsevanih z radikalnim namenom in intenzitetno modulirano (IMRT) oz. volumetrično modulirano ločno terapijo (VMAT). Razporedili smo jih v 6 skupin glede na časovno obdobje obsevanja in obsevalni aparat. V skupinah 1 in 2 (leto 2014) so bili vključeni bolniki, pri katerih so bile uporabljene standardne podlage za glavo in vrat, v ostalih skupinah (3-6, leti 2015 in 2017) pa bolniki z individualnimi podlagami. S pomočjo interfrakcijskih premikov na elektronskih portalnih slikah (EPI) smo analizirali sistematično in naključno populacijsko napako ter velikost varnostnega roba od kliničnega (CTV) do planirnega tarčnega volumna (PTV). Rezultati: Rezultati kažejo odstopanje interfrakcijskih premikov v posteriorno in inferiorno smer. Največja razlika interfrakcijskih premikov med standardnimi in individualnimi podlagami se pojavlja v anteroposteriorni (AP) smeri, sledi ji superoinferiorna (SI), najmanjše razlike je mogoče opaziti v mediolateralni (ML) smeri. Z uporabo individualnih podlag se sistematične in naključne napake večinoma zmanjšujejo – od 0,1 do 0,5 mm. Zaradi manjših sistematičnih in naključnih napak se z uvedbo individualnih podlag posledično zmanjša tudi CTV-PTV varnostni rob in sicer znaša v AP smeri 3,3 mm, 2,6 mm v SI in 3,2 mm v ML smeri. S p-vrednostjo p<10-3 lahko potrdimo statistično značilne razlike med interfrakcijskimi premiki pri uporabi standardnih oz. individualnih podlag. Razprava in zaključek: Dokazali smo, da uporaba individualnih podlag vpliva na zmanjšanje povprečnih interfrakcijskih premikov in števila povprečnih premikov izocentra. Pri standardnih podlagah je bila izračunana večja sistematična in individualno napaka ter opaženo večje število nedopustnih napak. 4 mm varnostni rob zagotavlja, da 90% bolnikov prejme vsaj 95% minimalne kumulativne doze na CTV.

• Language: Slovenian
• Keywords: individualne podlage, interfrakcijski premiki, nastavitvene napake, rak glave in vratu, portalno slikanje
• Work type: Master's thesis/paper
• Organization: ZF - Faculty of Health Sciences
• Year: 2018
• PID: 20.500.12556/RUL-105849
• COBISS.SI-ID: 5560683
• Publication date in RUL: 20.12.2018

Secondary language

• Language: English
• Title: Assessment of set-up errors in radiotherapy of patients with head and neck cancer: the importance of individual headrest : master thesis

Abstract

Introduction: The importance of evaluating interfractional movements in head and neck radiotherapy is crucial, since even small displacement can produce overdose of critical structures nearby or underdose the target volume. A solution to reduce set-up errors and safety margins is repeatable and certain immobilization, such as usage of individual headrest. Purpose: The purpose of this research was to evaluate the importance of individual headrest in head and neck radiotherapy, to calculate interfractional movements, systematic and random error and to compare optimum safety margin between group with individual and standard headrest. Methods: In present study we included 120 patients with head and neck cancer, radically treated with intensity modulated (IMRT) or volumetric modulated radiation therapy (VMAT). They were divided into 6 groups, considering linear accelerator and time period in which they were treated. Groups 1 and 2 represented patient with standard headrest, and the rest of them, ones with individual. Systematic population and random population errors were evaluated, based on interfractional movements, that were measured on daily pre-treatment electronic portal images (EPI). Also the optimum safety margins of clinical and planning target volume, according to van Herk, were calculated. Results: The substantial interfraction movements show in posterior and inferior direction. The major difference between individual and standard headrest is represented in anteroposterior (AP) direction and inconsiderable in mediolateral (ML) direction. Since the individual headrest have been in use, systematic and random errors have mostly reduced: for about 0,1 - 0,5 mm. Consequently narrower PTV-CTV margin is neeeded, to be specific - 3,3 mm in AP, 2,6 mm in SI and 3,2 mm in ML direction. Discussion and conclusion: Conclusion, based on the results, shows that imobilization with individual headrest reflects in minor interfractional movements and lower frequency of isocenter correction. Statistically significant differences (p<10-3) were found between individual and standard headrests. An extenstion, no greater than 4 mm, of clinical target volume margin ensures that 90% of patients will recieve a minimum cumulative dose greater than 95% of the prescribed dose.

• Keywords: individual headrest, interfractional movements, set-up errors, head and neck cancer, electronic portal imaging