Stereotactic body radiation therapy for pancreatic cancer: Assessing motion with and without abdominal compression.

Abstract

234 Background: Stereotactic body radiation therapy (SBRT) is an emerging treatment option for locally advanced pancreatic cancer. This ablative therapy requires highly accurate delivery due to nearby organs at risk. To minimize tumor motion, our institution applies abdominal compression during computed tomography (CT) simulation. The purpose of this study is to evaluate the effect of compression in the context of pancreatic SBRT. Methods: In the last 6 months, 32 patients who completed SBRT to the pancreas at our institution were selected for analysis. In each patient, two 4DCT images were acquired, one with and one without abdominal compression. Abdominal compression was achieved with an indexed compression belt with a customized degree of inflation. Each patient had fiducial markers implanted in or near the pancreatic tumor prior to simulation. These fiducials were contoured on both planning CT scans for each gated phase. Motion was assessed by fiducial position changes throughout each gated phase. Results: In the anterior to posterior, transverse, and superior to inferior dimension, compression decreased motion in 19 of 32 cases (59%), 21 of 32 cases (66%), and 28 of 32 cases (88%) respectively. In the anterior to posterior (AP) dimension compression decreased motion by a mean of 0.43mm ± 1.7mm with a range of -2.1-6.5mm (p = 0.16). The mean decrease in motion with compression in the transverse dimension was 0.93mm ± 1.9mm with a range of -1.6-8.6mm (p = 0.01). In the superior to inferior dimension, compression decreased motion by a mean of 2.72mm ± 2.8mm with a range of -1.2-11.5mm (p < 0.001). Displacement of tissue due to compression led to increased patient AP separation at the level of T12 by a mean of 9.1±5.8mm (p < 0.001). Conclusions: Abdominal compression significantly reduced tumor motion in the superior to inferior and transverse directions for patients undergoing SBRT to the pancreas. This decrease in motion allows for significant reductions in the size of the volume necessary to treat the tumor. Given our findings, we would recommend using abdominal compression over free-breathing for pancreatic SBRT.