Author/Editor		Stavrev, Pavel; Hristov, Dimitre
Title		Prostate IMRT fractionation strategies: two-phase treatment versus simultaneous integrated boost
Translated title		Radiobiološka primerjava dveh optimiziranih načinov obsevanja (IMRT) prostate: obsevanja v dveh delih in istočasnega visokodoznega obsevanja na manjše polje
Type		članek
Source		Radiol Oncol
Vol. and No.		Letnik 37, št. 2
Publication year		2003
Volume		str. 115-26
Language		eng
Abstract		Background. The purpose of the study was to investigate the radiobiological effect of the number of fractions, position uncertainties and clonogen spread (microscopic disease) on two different inverse treatment planning alternatives: (a) 2-phase strategy; (b) simultaneous integrated boost (SIB). Material and methods. The tumour control probability (TCP) and normal tissue complication probability (NTCP) were calculated for the 2-phase strategy, which has well defined fractionation scheme and compared to the TCP and NTCP for the SIB strategy calculated as a function of the number of fractions. For a 7-beam IMRT prostate treatment, we have performed inverse treatment planning for the two different strategies following the above method. Results. When the position uncertainties and clonogen spread were accounted for in the TCP calculation a drop as large as 10% was found. A drop of 5-7% in the TCP was obtained for the SIB strategy, if delivered in the same number of fractions as the 2-phased one. Conclusions. The potential of inverse planning to design tight conformal dose distributions is fully revealed in the SIB optimiyation process. The optimized SIB superior does distributions require modification of the delivered dose per fraction and therefore careful selection of the fractionation regime. Hence physically optimized SIB treatments may not always lead to better tumour control and tissue sparing.
Summary		lzhodišča. Namen raziskave je bil proučiti radiobiološki učinek števila frakcij obsevanja, natačnost namestitve bolnika med obsevanjem in klonogenost raka prostate glede na dva različna optimizirana načina obsevanja:-obsevanja v dveh delih in sočasnega visokodoznega obsevanja na manjše polje (simultaneous integrated boost -SIB). Material in metode. Verjetnost kontrole tumorja (TCP) in verjetnost poškodbe normalnega tkiva (NTCP) smo izračunali za obsevanje v dveh delih z natačno določenim frakcioniranjem obsevanja in ju primerjali s TCP in NTCP pri obsevanju s SIB načinom, pri čemer smo upoštevali odvisnost od števila frakcij. Za oba načina obsevanja smo uporabili metodo inverznega planiranja in obsevali prostate s 7 polji (IMRT). Rezultati. Ob upoštevanju natančnosti namestitve bolnika med obsevanjem in klonogenosti raka prostate smo izračunali, da se je TCP znižal za 10%. Če smo pri obsevanju s SIB načinom uporabili enako število frakcij kot pri obsevanju v dveh delih, se je TCP zmanjšal za 5-7%. Zaključki. Pri obsevanju s SIB načinom je razvidna prednost inverznega planiranja obsevanja za dosego konformne dozne porazdelitve. Metoda pa zahteva spremembo doze na frakcijo in tako tudi ustrezno prilagoditev frakcioniranja obsevanja. S fizikalnim optimiziranjem doze torej ne dosežemo vedno boljše kontrole tumorja pa tudi ne boljše ohranjanje zdravega tkiva.
Descriptors		PROSTATIC NEOPLASMS RADIOTHERAPY DOSAGE DOSE-RESPONSE RELATIONSHIP, RADIATION