(Wednesday, 8/1/2018) 1:45 PM - 3:45 PM
Room: Karl Dean Ballroom B1
Purpose: There is a lack of objective data in determining motion thresholds for SBRT. We 1) developed a technique to compute the maximum amount of motion allowable during treatment for individual patients, and 2) applied the technique on pancreatic SBRT data. The purpose of this work is to develop a pre-treatment framework for making motion management decisions.
Methods: The technique is described as follows. (1) Use a database of patient-measured tumor motion to calculate motion-convolved dose of the gross tumor volume (GTV) and the organs at risk (OARs). (2) Model the relationship between motion and changes in key dose metrics. (3) Apply these models to compute the amount of motion that can be allowed without exceeding critical dose metrics. We demonstrated this technique on 25 pancreatic SBRT patients and studied the effects of dose escalation and tumor volume on allowable motion.
Results: Our method was able to calculate allowable motion thresholds for each individual patient. In pancreatic SBRT, the mean [minimum-maximum] allowable motion for 33/40/50 Gy to the PTV was 11.9 [6.3—22.4], 10.4 [5.2—19.1] and 9.0 [4.2—16.0] mm, respectively. The allowable motion decreased as dose was escalated, and was smaller in patients with larger tumors, yet the largest variations stemmed from differences between patients.
Conclusion: Knowing the amount of motion allowable for a given plan allows one to select the proper motion management technique (e.g. abdominal compression or respiratory gating). In pancreatic SBRT, motion must be kept lower than 6.3 mm to ensure safe treatment of all patients at 33 Gy/5 fractions, yet differences between patients could allow for a more relaxed approach in some cases. The technique we present in this work has the potential to be used to develop patient-specific motion management plans.
Funding Support, Disclosures, and Conflict of Interest: Funding: This work was funded in part by the NIH K12CA086913, the University of Colorado Cancer Center/ACS IRG#57-001-53, the Boettcher Foundation, and Varian Medical Systems. Disclosures: Authors Campbell, Jones, and Miften have filed a provisional patent application for the fiducial marker tracking technique used in this work.
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