Investigation of pelvic floor influence on prostate displacement in image‐guided radiotherapy

Purpose The uncertainty of target location during prostate cancer radiotherapy plays an important role in accurate dose delivery and radiation toxicity in adjacent organs. This study analyzed displacement correlations between the prostate and pelvic floor. Methods and Materials We retrospectively analyzed registration results from 467 daily cone‐beam computed tomography (CT) in 12 patients with prostate cancer who received radiation therapy. We analyzed prostate displacement and the pelvic floor relative to the pelvic bone's anatomy in the translational and rotational directions and identified statistical correlations. Results The systematic (Σ) and random (σ) displacements of the prostate in the three translational directions, anterior–posterior (AP), superior–inferior (SI), and right–left (RL), were 1.49 ± 1.45, 2.10 ± 1.40, and 0.24 ± 0.53 mm, respectively, and in the rotational directions of the pitch, roll, and yaw were 2.10 ± 2.02°, 0.42 ± 0.74°, and 0.42 ± 0.64°, respectively. The pelvic floor displacements were 2.37 ± 1.96, 2.71 ± 2.28, and 0.47 ± 0.84 mm in the AP, SI, and RL directions, respectively, and 0.93 ± 1.49°, 0.98 ± 1.28 °, and 0.87 ± 0.94° in the pitch, roll, and yaw directions, respectively. Additionally, there were statistically significant correlations between the displacement of the prostate and pelvic floor in the AP and SI directions, with correlation coefficients (r) of 0.74 (p