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SU‐E‐P‐25: Evaluation of Motion in Pancreas SBRT Treatment Deliveries
Author(s) -
Xiong L,
Halvorsen P
Publication year - 2015
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4923959
Subject(s) - fiducial marker , medicine , nuclear medicine , margin (machine learning) , standard deviation , image guided radiation therapy , radiation therapy , radiosurgery , dosimetry , motion (physics) , radiology , physics , mathematics , computer science , statistics , classical mechanics , machine learning
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.