SU-E-P-25: Evaluation of Motion in Pancreas SBRT Treatment Deliveries

Authors


Abstract

Purpose:

Stereotactic Body Radiation Therapy (SBRT) procedures for pancreatic cancer present a challenge in motion management because the target is directly adjacent to critical structures and the target is subject to significant respiratory motion. Gated treatment is usually planned with a tight (few mm) PTV margin. The positioning and setup relies on on-board-imaging (OBI) of internal fiducials. This study evaluates the corrections for inter- and intra-fractional target motion as evidenced by the OBI.

Methods:

20 patients with gated pancreas SBRT treatment were setup with KV imaging guidance before and during each treatment. The couch position was fine-tuned to align with the internal fiducials for each patient. The data for 148 intra- and 111 inter-fractional couch movements were captured and analyzed.

Results:

The mean ± standard deviation of couch shifts for the initial daily setup is 4.9±4.1 mm for couch vertical, 5.3±4.6 mm for couch longitudinal, and 3.7±4.0 mm for couch lateral. The mean ± standard deviation of intra-treatment adjustments are 1.1±1.6, 2.5±3.8, and 1.1±1.8 mm for couch vertical, longitudinal and lateral. The probability of intra-fractional motion in the three orthogonal directions with magnitude no more than 2 mm, 3 mm and 5 mm is 55%, 68% and 84% respectively.

Conclusion:

The intra-treatment target motion for pancreas SBRT patients indicates that a PTV margin of 5mm may be necessary.

Ancillary