Investigation of six-degree-of-freedom image registration between planning and cone beam computed tomography in esophageal cancer

Abstract

Objective To explore six-degree-of-freedom (6-DF) registration methods between planning and cone beam computed tomography (CBCT) during image-guided radiation therapy (IGRT) in esophageal cancer.Methods Thirty pairs of CBCT images acquired before radiation and the corresponding planning computed tomography (CT) images of esophageal cancer were selected for further investigation.Registration markers for 6-DF image registration were determined and contoured in those images.The results of registration as well as time cost were compared among different registration methods of bone match, gray value match, manual match, and bone plus manual match.Results Contouring bone and spinal canal posterior to the target volume of esophageal carcinoma as registration marker could make 6-DF registration quick and precise.Compared with manual match, set-up errors of v rotation in bone plus manual match (-0.55° vs.-0.88°, t=2.55, P=0.020), of x-axis and v rotation in bone match (0.12 mm vs.-2.33 mm, t=5.75, P=0.000; -0.35° vs.-0.88°, t=3.00, P=0.007), and of x-axis and w rotation in gray value match (7.20 mm vs.-2.33 mm, t=3.10, P=0.006; -0.10° vs.-0.59°, t=2.81, P =0.011) were significantly different.Compared with manual match, the coincidence rate of bone plus manual match was the highest (85.55%), followed by bone match and gray value match (74.45% and 74.45%).The time cost of each registration method from longest to shortest was:6.00 -10.00 minutes for manual match, 1.00 - 5.00 minutes for bone plus manual match, 0.75 - 1.50 minutes for gray value match, and 0.50 - 0.83 minutes for bone match.Conclusions Registration marker is useful for image registration of CBCT and planning CT in patients with esophageal cancer.Bone plus manual match may be the best registration method considering both registration time and accuracy. Key words: Esophageal neoplasms/radiotherapy; Radiotherapy, image-guided; Image registration marker; Image registration method