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Quantifying the Ability of Tumor Tracking to Spare Normal Tissue

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A Burger

A Burger1*, I Buzurovic1 , M Hurwitz1 , P Mishra2 , C Williams1 , J Seco3 , J Lewis1 , (1) Brigham and Women's Hospital, Dana-Farber Cancer Center, Harvard Medical Sc, Boston, MA, (2) Varian Medical Systems, Palo Alto, CA, (3) Mass General Hospital; Harvard Medical, Boston, MA


SU-D-18A-4 Sunday 2:05PM - 3:00PM Room: 18A

Tumor tracking allows for smaller tissue volumes to be treated, potentially reducing normal tissue damage. However, tumor tracking is a more complex treatment and has little benefit in some scenarios. Here we quantify the benefit of tumor tracking for a range of patients by estimating the dose of radiation to organs at risk and the normal tissue complication probability (NTCP) for both standard and tracking treatment plans. This comparison is performed using both patient 4DCT data and eXtended Cardiac-Torso (XCAT) digital phantoms.

We use 4DCT data for 10 patients. Additionally, we generate digital phantoms with motion derived from measured patient long tumor trajectories to compare standard and tracking treatment plans. The standard treatment is based on the average intensity projection (AIP) of 4DCT images taken over a breath cycle. The tracking treatment is based on doses calculated on images representing the anatomy at each time point. It is assumed that there are no errors in tracking the target. The NTCP values are calculated based on RTOG guidelines.

The mean reduction in the mean dose delivered was 5.5% to the lungs (from 7.3 Gy to 6.9 Gy) and 4.0% to the heart (from 12.5 Gy to 12.0 Gy). The mean reduction in the max dose delivered was 13% to the spinal cord (from 27.6 Gy to 24.0 Gy), 2.5% to the carina (from 31.7 Gy to 30.9 Gy), and 15% to the esophagus (from 69.6 Gy to 58.9 Gy). The mean reduction in the probability of 2nd degree radiation pneumonitis (RP) was 8.7% (3.1% to 2.8%) and the mean reduction in the effective volume was 6.8% (10.8% to 10.2%).

Tumor tracking has the potential to reduce irradiation of organs at risk, and consequentially reduce the normal tissue complication probability. The benefits vary based on the clinical scenario.

Funding Support, Disclosures, and Conflict of Interest: This study is supported by Varian Medical Systems, Inc.

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