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4D Particle Swarm Optimization to Enable Lung SBRT in Patients with Central And/or Large Tumors

A Modiri

A Modiri*, X Gu , A Hagan, A Sawant , UT Southwestern Medical Center, Dallas, TX


SU-E-T-6 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Patients presenting with large and/or centrally-located lung tumors are currently considered ineligible for highly potent regimens such as SBRT due to concerns of toxicity to normal tissues and organs-at-risk (OARs). We present a particle swarm optimization (PSO)-based 4D planning technique, designed for MLC tracking delivery, that exploits the temporal dimension as an additional degree of freedom to significantly improve OAR-sparing and reduce toxicity to levels clinically considered as acceptable for SBRT administration.

Two early-stage SBRT-ineligible NSCLC patients were considered, presenting with tumors of maximum dimensions of 7.4cm (central-right lobe; 1.5cm motion) and 11.9cm (upper-right lobe; 1cm motion). In each case, the target and normal structures were manually contoured on each of the ten 4DCT phases. Corresponding ten initial 3D-conformal plans (Pt#1: 7-beams; Pt#2: 9-beams) were generated using the Eclipse planning system. Using 4D-PSO, fluence weights were optimized over all beams and all phases (70 and 90 apertures for Pt1&2, respectively). Doses to normal tissues and OARs were compared with clinically-established lung SBRT guidelines based on RTOG-0236.

The PSO-based 4D SBRT plan yielded tumor coverage and dose–sparing for parallel and serial OARs within the SBRT guidelines for both patients. The dose-sparing compared to the clinically-delivered conventionally-fractionated plan for Patient 1 (Patient 2) was: heart Dmean = 11% (33%); lung V20 = 16% (21%); lung Dmean = 7% (20%); spinal cord Dmax = 5% (16%); spinal cord Dmean = 7% (33%); esophagus Dmax = 0% (18%).

Truly 4D planning can significantly reduce dose to normal tissues and OARs. Such sparing opens up the possibility of using highly potent and effective regimens such as lung SBRT for patients who were conventionally considered SBRT non-eligible. Given the large, non-convex solution space, PSO represents an attractive, parallelizable tool to successfully achieve a globally optimal solution for this problem.

Funding Support, Disclosures, and Conflict of Interest: This work was supported through funding from the National Institutes of Health and Varian Medical Systems.

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