Room: Exhibit Hall | Forum 5
Purpose: To determine the reproducibility of gross target position over sequential inspiratory breath holds guided by the Varian RPM system in treatments of the pancreas and liver.
Methods: All patients in this study were enrolled in an IRB-approved retrospective protocol. This study includes fourteen patients treated for liver disease and ten patients treated for pancreas disease. At the time of simulation, a 4DCT was acquired to measure the motion of the gross disease during normal respiration. Patients evaluated for RPM-guided inspiratory breath hold (IBH) treatment had five CT images acquired at IBH following the 4DCT. Prior to the IBH scans, a target range 4-5 mm wide for the breath hold amplitude was determined based on observed variation in breath-hold amplitude over 5-8 breath holds. For each patient, the last four IBH images were registered to the first IBH image, first focusing on the spine at the level of disease using 6D corrections, then focusing on the gross disease using only translational corrections. The translational correction required to align the gross disease was recorded as the displacement in the position of the gross disease between breath holds.
Results: The mean displacement in the position of the gross disease across all patients was (0.3, -0.3, 1.0) mm along the left-right, anterior-posterior, and superior-inferior axes, respectively, indicating that on average the breath hold for the first scan was the deepest. The systematic uncertainty in the displacement of the gross disease was (0.6, 0.6, 1.4) mm, while the random uncertainty was (0.7, 1.0, 1.7) mm. The mean 3D displacement of the gross disease across all patients was 2.2Â±1.7 mm. No significant difference in displacement of gross disease was observed between liver and pancreas targets.
Conclusion: Respiratory motion reduction of liver and pancreas tumors is possible with IBH treatment using Varian RPM system guidance.