Exhibit Hall | Forum 2
Purpose: With the clinical implementation of kV-CBCT based daily online-adaptive radiotherapy the ability to monitor, quantify and correct for patient movement during adaptive sessions is paramount. With sessions lasting between 20-45mins, having the ability to detect and correct for small movements without restarting the entire session is critical to the adaptive workflow and dosimetric outcome. The purpose of this study was to quantify and evaluate the correlation of observed patient movement with machine logs and a surface guided imaging(SGRT) system during adaptive radiation therapy.
Methods: Ethos machine logs and IDENTIFY registration data log files (Varian Medical Systems) for 525 individual sessions were exported and analyzed. For each session, the calculated shifts from a pre-delivery position verification CBCT were extracted from the machine logs and compared to the IDENTIFY registration data log files captured during motion monitoring. For the IDENTIFY log files, the total movement was calculated by taking the difference between the 5 seconds immediately pre and post shift. The IDENTIFY calculated shifts were compared to the reported shifts of the machine logs to determine similarity and correlation.
Results: The average(±STD) net displacement of the IDENTIFY shifts were 2.5±2.3mm, 2.2±2.1mm, 3.0±2.7mm in the vertical, lateral, longitudinal directions respectively. For the Ethos machine logs, the net displacement in the vertical, lateral, longitudinal directions were 2.3±3.0mm, 2.2±3.3mm, and 2.1±3.1 mm. The average difference(IDENTIFY–Ethos), was -0.1±4.2mm, -0.1±3.8mm, and 1.2±4.7mm, for the vertical, lateral, and longitudinal directions. On average, a movement of 4.5±4.1mm and 5.1±3.9mm was calculated prior to delivery for the CBCT and SGRT system respectively. A Pearson correlation coefficient of r=0.65 was calculated.
Conclusion: Surface imaging should be used to monitor and quantify patient movement during adaptive radiotherapy. However, it does not replace the need for a pre-delivery verification CBCT, especially in clinical sites prone to anatomical changes during the adaptive process.