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Active Breathing Controlled Intra-Fractional Liver Motion Is Patient Specific

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L Lu

L Lu*, C Diaconu , S Lin , T Djemil , G Videtic , M Abdel-Wahab , N Yu , J Greskovich , K Stephans , P Xia , Cleveland Clinic, Cleveland, OH


TH-AB-205-9 (Thursday, August 3, 2017) 7:30 AM - 9:30 AM Room: 205

Purpose: Active breathing control (ABC) for patients with liver tumors treated with SBRT is frequently used in our clinic. This study is to analyze reproducibility of intra-fractional liver motion using three CT scans acquired during simulation.

Methods: Forty-four patients with hepatic tumor who were compliant with breath-holding were treated with SBRT under ABC. All patients received three consecutive CTs under ABC at simulation to test reproducibility of breath-holding. For each patient, the planning target volume (PTV) and liver were contoured on the first CT (ABC1), which was used for treatment planning. For this study, the liver contour on the CT of ABC1 was propagated to CTs of ABC2 and ABC3 through deformable image registration and manual editing. The differences in centroids of the whole livers among the three ABCs were measured to assess intra-fraction variability.

Results: Average absolute intra-fractional liver motions were 0.73±0.71 mm, 1.8±2.51 mm, and 2.16±2.61 mm at medial-lateral (ML), anterior-posterior (AP), and superior-inferior (SI) directions, respectively. All shifts at ML direction (range -3.9 to 2.0 mm) were within 5 mm, however, 7% of shifts (range -10.5 to 16.7 mm) and 11% of shifts (range -17.0 to 8.7 mm) exceeded 5mm at AP and SI directions, respectively. A histogram of the data showed the intra-fractional liver motion were not reproducible for some patients. 16% of this cohort had the displacement of liver centroid greater than 5mm. Those large intra-fractional liver motions should be considered during treatment planning for these specific patients.

Conclusion: From this study, the majority (84%) of the patients had small intra-fractional shifts (<5mm) in liver position, which has been included into our SBRT planning margin. Large intra-fractional liver motion was observed for small number of patients, for whom patient specific planning margins are necessary.

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