Setup Reproducibility of Supine Position in Radiotherapy of Rectal Cancer Patients

Abstract

Setup reproducibility is crucial in the delivery of dose in radiotherapy as it determines the accuracy and treatment success of the procedure. Previous studies reported supine as an alternative to prone; however, the comparison was not straightforward as several factors were overlooked. This retrospective study attempted to determine the setup reproducibility as measured by displacement of bony landmarks in the lateral, longitudinal, and vertical axes of supine position relative to the standard prone position. Sixteen rectal cancer patients were positioned in supine (N=6) and prone (N=10) as per radiation oncologists and medical physicists in 2018. On each daily fraction, the displacement of the bony landmark in the three axes was calculated by the medical physicists and radiation therapists, and a total of 61 measurements were recorded. Results revealed that both supine and prone positions demonstrated an unacceptable reproducibility value. The setup reproducibility did not significantly differ in both positions. Based on the results of the study, the supine position, as reported by previous studies to exhibit superior setup reproducibility than prone position, is still unacceptable in radiotherapy of rectal cancer patients.