Room: Exhibit Hall | Forum 5
Purpose: Adaptive radiotherapy (ART) has the potential to reduce toxicity and facilitate safe dose escalation. Dose calculations with the planning CT deformed to cone beam CT (CBCT) have shown promise for estimating the â€œdose of the dayâ€?; however, none have investigated it for lung cancer patients receiving photon RT. The purpose of this study was to investigate the accuracy of the â€œdose of the dayâ€? calculations based on CBCT and deformable image registration (DIR) for locally advanced lung cancer.
Methods: We studied 12 lung cancer patients, for which daily CBCT imaging was performed to align patients. A replanning CT (rCT) was also acquired after 16-20 Gy for all patients. A virtual CT (vCT) was created by DIR between the initial planning CT and CBCT acquired on the same day as rCT. Dose calculations were performed with the vCT and rCT, followed by DIR-based dose accumulation. We evaluated agreements between the vCT-based accumulated dose-volume metrics and rCT-based metrics as reference using the Bland-Altman analysis.
Results: Mean differences between the vCT-based accumulated dose-volume metrics and rCT-based metrics were smaller than 1.5%, and most subjects fell within the range of Â±5% for the target volume, lung, esophagus and heart. For the spinal cord maximum dose, a large mean difference of -5.6% was observed, which was largely attributed to two subjects with DIR errors caused by very limited CBCT image quality (e.g., truncation artifacts).
Conclusion: This study demonstrated a reasonable agreement between the virtual CT-based and replanning CT-based accumulated dose-volume metrics, with the exception of cases where CBCT image quality was very limited. These findings suggest the potential for the virtual CT to provide an accurate estimate of the â€œdose of the dayâ€? for locally advanced lung cancer, and it could be used as a tool to facilitate ART.
Funding Support, Disclosures, and Conflict of Interest: This study was supported by the National Key R&D Program of China (2016YFC0103400), the American Cancer Society, and the Dean of the UC Davis School of Medicine (ACS IRG-95-125-13) (T.Y. and M.E.D.). The authors declare no conflicts of interest.