Minimizing Bowel Gas Artifact in Computed Tomography Guided Online Adaptive Radiation Therapy With Prolonged Supine Positioning.

Abstract

Abdominal computed tomography guided online adaptive SABR treatments can be complicated by bowel gas artifact. We investigated whether prolonged patient supine positioning decreases bowel gas artifact. Three radiation oncologists, a physicist, and an advanced practice radiation therapist scored bowel gas artifact in 1644 images from 104 cone beam computed tomography (CBCT) data sets acquired in 52 fractions delivered to 26 pancreatic adenocarcinoma patients with a Halcyon/Ethos online adaptive SABR platform. Bowel gas artifact scoring followed an ordinal rubric from 1 (best) to 4 (worst). Ten patients were imaged with HyperSight CBCTs and 16 with an earlier CBCT imager, Halcyon v3.0. Four-hundred forty-four CBCT images (27%) had bowel gas artifact that at least minimally obscured organ-at-risk borders. Artifact was worse in initial CBCTs than subsequent verification CBCTs (mean scores 2.26 vs 2.15, P = .006). The proportion of images scored 4 was significantly greater in Halcyon initial CBCTs (0.25) compared to verification CBCTs (0.16; P < .001). For HyperSight, this proportion was low in initial CBCTs (0.03) and lower in verification CBCTs (0.01; P = .09). Clinically impactful bowel gas artifact in online adaptive SABR CBCT data sets was better in verification CBCTs than in initial CBCTs, potentially due to bowel settling during prolonged supine positioning.