Purpose: To quantify pancreas and pancreatic tumor movement due to respiratory motion using volumetric cine CT images.
Materials and methods: Six patients with pancreatic tumors were scanned in cine mode with a 256 multi-slice CT scanner under free breathing conditions. Gross tumor volume (GTV) and pancreas were manually contoured on the CT data set by a radiation oncologist. Intrafractional respiratory movement of the GTV and pancreas was calculated, and the results were compared between the respiratory ungated and gated phases, which is a 30% duty cycle around exhalation.
Results: Respiratory-induced organ motion was observed mainly in the anterior abdominal side than the posterior side. Average GTV displacement (ungated/gated phases) was 0.7 mm/0.2mm in both the left and right directions, and 2.5mm/0.9 mm in the anterior, 0.1 mm/0mm in the posterior, and 8.9 mm/2.6mm in the inferior directions. Average pancreas center of mass displacement relative to that at peak exhalation was mainly in the inferior direction, at 9.6mm in the ungated phase and 2.3mm in the gated phase.
Conclusions: By allowing accurate determination of the margin, quantitative analysis of tumor and pancreas displacement provides useful information in treatment planning in all radiation approaches for pancreatic tumors.