ESTRO 2024 - Abstract Book

S5619

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2024

CBCT image quality has been shown to be inferior to planning CT 1 . Specifically for pancreas, this is amplified by poor contrast, motion, and gas and stent artefacts 2,3 . Multiple sources of motion and inferior quality impact the observer’s ability to perform on-treatment registration, and affect decision making. Breath-hold cone-beam CT (CBCT_BH) image acquisition has the potential to improve image quality. This has not been quantified for pancreas patients with most emphasis being placed on volume reduction, rather than the benefits of improved image quality. The aim of this study was to evaluate improvement in subjective overall image quality (OQ) comparing CBCT_BH imaging to free-breathing CBCT (CBCT_FB). Patients who had completed RT for pancreatic ductal adenocarcinoma (PDAC) were included. Images were acquired on a Truebeam linear accelerator (Varian Medical Systems, Palo Alto, CA), CBCT exposure settings of 45mA, 125 kV, 805mAs. CBCT_BH was acquired using the Real Time Position Management (RPM) System (Varian Medical Systems, Palo Alto, CA). BH threshold was set to +/- 2mm. Two sets of paired image datasets were randomly selected from six consecutive patients. Oral contrast (5-10ml diluted in 125/250ml water) was administered before imaging. Scoring criteria were developed based on previous lung studies 4,5 (Figure 1). An assessment was made of OQ, visualisation of celiac artery (CA), superior mesenteric artery (SMA), superior mesenteric vein (SMV), duodenum (DUO), gross tumour/internal target volume (GTV/ITV) and PTV. Each group of observers consisted of 2 therapeutic radiographers (RTT) who scored the images as per criteria. These included an expert RTT group (EXP) and clinical RTT observer groups (OBS). Material/Methods: