208. Investigation on target motion with intraprostatic fiducial markers and daily CBCT in radical radiotherapy for prostate cancer

Purpose Nowadays there is a great interest on the improvement of the patient setup variability and target motion in radical radiotherapy for prostate cancer thanks to the fiducial markers inside the target [1] . The prostate lies in proximity to hollow organs (bladder and rectum) which are at risk of toxicity and may be displaced due to filling of these organs. To assess the utility of this method, we evaluated setup and target motion errors with daily fiducial-based CBCT in prostate image-guided radiotherapy; the radio-opaque seeds makes possible to monitor the previous discussed soft tissue structures. Methods Ten patients with prostate adenocarcinoma at intermediate-risk underwent radical radiotherapy with RapidArc technique and daily CBCT. They were previously subjected to intra-prostatic radio-opaque fiducial markers implantation. PTV included prostate and seminal vesicles. Patients were aligned to the treatment isocenter by laser. During treatment, daily CBCT were acquired and a matching according to fiducials was performed. After that, coach shifts required for isocenter correction were carried out. We measured lateral-lateral (LL), anterior-posterior (AP) and cranial-caudal (CC) shift adjustments. Results Mean and Standard Deviation of shifts in longitudinal, vertical and lateral directions signed in daily CBCT-matching according to fiducial markers for each patient were estimated as reported in Fig. 1. As a preliminary result, lateral shift mean is higher than the other two, whereas longitudinal and vertical shifts are affected by higher standard deviation. It could be due to the inter-fraction morphologic variations of patients. Conclusions The correct reproducibility of prostate treatment is affected by setup error and organ motion. Daily IGRT with fiducial-based CBCT ensures accuracy of the treatment since it is able to track the target position, mainly in the modern radiotherapy techniques with dose escalation to the target. Download : Download high-res image (215KB) Download : Download full-size image