Inter- and intrafractional variation in the three-dimensional positions of pancreatic tumors due to respiration under real-time monitoring

Abstract Purpose/Objective To quantify the three-dimensional pancreatic tumor motion during the overall treatment course using real-time orthogonal kV X-ray imaging. Methods and Materials This study included 10 patients with pancreatic cancer who underwent six-port static intensity modulated radiation therapy with real-time tumor tracking in 15 fractions, except for one patient (5 fractions). The tumor and abdominal wall positions were acquired simultaneously during the overall treatment course. Then, the tumor motion amplitude and reference positions were determined. Results The mean tumor amplitudes were 4.9, 6.5, and 13.4 mm in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively. The intrafractional variations of the reference tumor position were up to 5.4, 10.2, and 10.7 mm in the LR, AP, and SI directions, and those of the reference abdominal position were up to 10.5 mm. The reference tumor position drifted significantly in the AP and SI directions after 10 min, and that of abdominal wall motion drifted during the first 15 min ( p < 0.05). The interfractional variation of the reference tumor position after set-up correction, based on bony structures, was up to 8.9, 9.8, and 11.0 mm in the LR, AP, and SI directions, respectively. Conclusions Appropriate respiratory motion management techniques should be applied for the accurate localization of pancreatic tumors.