Author/Editor		Kasabašić, Mladen; Faj, Dario; Belaj, Nenad; Faj, Zlatan; Tomaš, Ilijan
Title		Implementing of the offline setup correction protocol in pelvic radiotherapy: safety margins and number of images
Translated title		Uvedba protokola za izvedbo ofline popravkov pri nastavitvah: varnostne meje in število slik
Type		članek
Source		Radiol Oncol
Vol. and No.		Letnik 41, št. 1
Publication year		2007
Volume		str. 48-55
Language		eng
Abstract		Background. Patient positioning errors in pelvic radiotherapy at Department of Oncology and Radiotherapy in Osijek are explored in order to establish the offline setup correction protocol and determine the safely margins. Material and methods. Film portal imaging is used during the whole treatment in order to find patient positioning errors. Eleven patients are included in the study and 420 images are analyzed. Setup errors are found by measuring distances between the center of the field and bony landmarks. Systematic and random errors are analyzed. Results. Safety margins that should be employed at our department are 11 mm, 13 mm and 14 mm in mediolateral, craniocaudal and anteroposterior direction, respectively. Time trend is found only in an aged, obese patient with a hip problem. No action level offline setup protocol was employed by taking and averaging first four images in mediolateral and craniocaudal and 5 images in anteroposterior direction. Conclusions. Since time tvend is found only in a patient who was hard to position because of his age, obesity and the hip problem, we decided that such patients are to be positioned without a bellyboard and in supine position. Time trends are not found in all of the other patients so we employed the offline setup error protocol by averaging setup errors from the first few consecutive images. Safety margins that will ensure 90% probability of depositing at least 95 % of the prescribed dose in the target are calculated. Safety margins and number of images that should be taken showed that the most inaccurate positioning was in the anteroposterior direction.
Summary		Izhodišča. Na Oddelku za onkologijo in radioterapijo Univerzitetne bolnice v Osjeku smo proučili, kakšne so napake pri nastavitvi pacientov ob radioterapiji v območju medenice. Izsledke smo uporabili za izdelavo protokola korekcij nastavitev in za določitev varnostnih robov. Bolniki in metode. Natančnosti nastavitve smo preverjali z gamagrafijo. V študijo smo vključili 11 bolnikov, obdelali pa smo 420 slik. Napake pri nastavitvi smo določali z meritvijo razdalj med centrom polja in značilnimi kostnimi točkami. Analizirali smo sistemske in naključne napake. Rezultati. Varnostni robovi, ki bi jih na našem oddelku morali upoštevati, so 11 mm v mediolateralni smeri, 13 mm v kraniokaudalni in 14 mm v anterioposteriorni smeri. V offline korekcijskem protokolu smo upoštevali povprečje prvih štirih gamagrafij za popravke v medio-lateralni in kranio-kavdalni smeri ter povprečje petih slik za popravke v anterio-posteriorni smeri. Zaključki. Natančnost nastavitve se med frakcijami ni bistveno spreminjala, razen pri enem bolniku. Tega bolnika je bilo posebno težko nastavljati zaradi njegovih let, debelosti in težav s kolkom. Odločili smo se, da bomo takšne paciente odslej nastavljali brez podlag za trebuh (bellyhoardov), na hrbet. Pri vseh ostalih bolnikih se natančnost nastavitve med frakcijami ni bistveno spreminjala. Za to smo uvedli offline nastavitveni protokol, pri katerem smo upoštevali povprečne napake pri prvih nekaj nastavitvah. Izračunali smo varnostne meje, za katere velja, da tarčni volumen z 90% gotovostjo obsega vsaj 95% predpisane doze. Varnostni robovi in variacije nastavitev kažejo, da je najnenatančnejše nastavljanje v anterioposteriorni smeri.
Descriptors		UTERINE NEOPLASMS RECTAL NEOPLASMS RADIOTHERAPY DOSAGE