Dozimetrični učinki intrafrakcijskih premikov organov pri brahiradioterapiji raka materničnega vratu : magistrsko delo

Marolt, Primož (author), Peterlin, Primož (mentor), Hudej, Robert (comentor)

Med obsevanjem z brahiradioterapijo s pulzno hitrostjo doze prihaja do premikanja organov v področju male medenice zaradi peristaltike in različne polnjenosti sečnega mehurja. Oddaljenost organov se s tem glede na aplikator in vir sevanja spreminja, kar lahko povzroči razliko med načrtovano in absorbirano dozo na kritičen organ. Doze na kritične organe preverjamo s pomočjo parametrov D0,1cm3 in D2cm3. Namen: Namen raziskave je ovrednotiti dozne razlike na kritične organe, nastale zaradi premikanja organov med brahiradioterapijo s pulzno hitrostjo doze. Metode dela: Raziskovalni vzorec predstavlja 15 bolnic z neoperabilnim rakom materničnega vratu, zdravljenih z magnetno resonačno slikovno vodeno brahiradioterapijo. Uporabljena sta bila klinično potrjen obsevalni načrt in kontrolni obsevalni načrt. Kontrolno magnetno resonačno slikanje je bilo opravljeno po koncu obsevanja. Pridobljene slike s ponovno vrisanimi organi so bile registrirane s kliničnimi slikami, ki so bile narejene za potrebe načrtovanja obsevanja. Opazovali in primerjali smo spremembo velikosti volumnov mehurja in danke ter razliko med obema obsevalnima načrtoma v dozi na 0,1cm3 in 2cm3 volumna mehurja, danke, sigmoidnega črevesa in tankega črevesa. Rezultati in razprava: Pri vseh bolnicah smo za mehur in danko med obema slikanjema z magnetno resonanco ugotovili premik oz. spremembo volumna vrisanih organov. Statistična obdelava podatkov kaže, da ne prihaja do statistično značilnih razlik v spremembi volumnov mehurja in danke med kliničnim in kontrolnim slikanjem. Pri opazovanju D2cm3 smo za danko odkrili statistično značilno razliko (p = 0,038), pri ostalih organih ni bilo statistično značilnih razlik. Z raziskavo nismo odkrili statistično značilnih razlik pri opazovanju D0,1cm3. Kljub povprečno majhnim razlikam v dozah med obema načrtoma prihaja v posameznih primerih do relativno velikih doznih razlik med obema obsevalnima načrtoma. Zaključek: V raziskavi smo dokazali, da se kritični organi med brahiterapijo s pulzno hitrostjo doze premikajo ali se spreminja njihov volumen. V povprečju so ti premiki majhni, prav tako nismo našli statistično značilnih razlik. Ugotovili smo tudi, da ne prihaja do statistično značilnih razlik pri opazovanem D2cm3 kritičnih organov, razen pri danki. V posameznih primerih prihaja do velikih razlik, zato bi veljalo razmisliti o kontrolnem magnetno resonančnem slikanju po 1. aplikaciji vsaj v primerih, ko so načrtovane doze blizu mejnih vrednosti.

• Language: Slovenian
• Keywords: intrafrakcijski premiki, brahiradioterapija, pulzna hitrost doze, kritični organi, D2cm3, D0, 1cm3, dozne omejitve, klinični obsevalni načrt, kontrolni obsevalni načrt, magnetno resonančno slikanje
• Work type: Master's thesis/paper
• Organization: ZF - Faculty of Health Sciences
• Year: 2017
• PID: 20.500.12556/RUL-97618
• COBISS.SI-ID: 5342571
• Publication date in RUL: 29.10.2017

Secondary language

• Language: English
• Title: Intrafractional organ motion in cervical carcinoma brachyradiotherapy: dosimetric impact : masterʹs thesis

Abstract

Introduction: During Brachytherapy treatment organs in pelvic region can move because of the peristaltic or different bladder filling. The result are differencies between planned and absorbed doses to organs at risk. We evaluate dose to the organ at risk with dose volume histogram parameters D2cm3 and D0,1cm3. Purpose: The purpose of this study is to evaluate impact of intrafractional organ motion on absorbed dose in organs at risk in cervical carcinoma brachytherapy during pulse dose rate brachytherapy. Materials and methods: In this study 15 patient with locally advanced Cervical cancer, treated with pulse dose rate brachytheapy after external beam radiotherapy and chemotherapy were observed. Clinicaly approved treatment plans and control plans were used. All plans were magnetic resonance imaging - based. Control magnetic resonance imaging was done after pulse dose rate irradiation. Clinically approved and control magnetic resonance images for each patient were registred together with respect to the applicator. We evaluated and compared volumes, D2cm3 and D0,1cm3 values for the bladder, rectum, sigmoid bowel and small intestine. Results and discussion: In all cases differences between observed bladder and rectum volumes were found. No statistically significant differences were found between the volumes between two scans of organ at risks. No statistically significant differences were found between two plans for organ at risks D2cm3 and D0,1 cm3, except for D2cm3 for the rectum (p = 0,038). We found no large average differences, but there were some large variations in D2cm3 observed for individual patients, which should be take into account. Similar results were reported in literature by other authors. Conclusions: The results show that organ at risks volumes change during pulse dose rate brachytherapy treatment, which results in dose varaiations. Although we found no large average differences, there were some large variations in D2cm3 observed, which should be taken into account, especially when on clinicaly approved treatment plan doses are close to the planning constraints.

• Keywords: intrafractional motion, brachyradiotherapy, pulse dose rate, organ at risk, D2cm3, D0, 1cm3, dose constraints, clinicaly approved treatment plan, control plan, magnetic resonance imaging