SU‐E‐T‐437: Dosimetry Study of Setup Errors in Intensity‐Modulated Radiotherapy of Cervical Cancer Post‐Surgery

Abstract

Purpose: To measure the setup errors by using cone beam computed tomography (CBCT) and to analyze the effect of the setup errors on the physics dose of targets and peripheral organs at risk (OARs) for cervical Cancer undergoing the intensity modu1ated radiation therapy (IMRT). Methods: Ten cervical Cancer cases were chosen at random. CBCT was performed before radiotherapy．The acquired CBCT were co‐ registered with the planning CT for online set‐up correction and errors of isocenter positions on x、y、z axes were obtained .Those were simulated in actual therapy on the treatment planning system (TPS)，and recalculated their dose distribution．A series of relative targets and OAR dose parameters were analyzed，and obtained the impact of the setup errors on the physics dose. Results: (1)A total of 126 CBCT scans were performed on 10 patients．The detection rates of deviation of ≤0.3cm were 92.86％ in left‐ to‐right (X) direction，83.33％ in superior‐to‐inferior (Y) direction， and 91.26％ in anterior‐to ‐posterior (Z)direction；The setup errors on X，Y and Z axes direction were(0.24±0.21)cm&#1 2289;(0.28±0.32)cm&#1 2289;(0.10士0.23)c m. (2) Dose and volumes index of CTV were no significant difference between simulated plans and actual plans. (3) V45、V50 of bladder and V30、V40、V45、V50 of rectum in simulated plans were significantly larger than those in actual plans，especially V45、V50 of rectum(P<0.005). Conclusions: The CBCT plays key ro1e in the guarantee of accurate delivery of IMRT for cervical Cancer,especially peripheral OARs.