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Evaluation of Proton Lung SBRT Plan Robustness to Daily Setup and Anatomy Variations

Y Lin

Y Lin1*, M Zhu2 , Q Wu1 , M Fang1 , F Yin1 , (1) Department of Radiation Oncology, Duke University Medical Center, Durham, NC, (2) Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD,


SU-I-GPD-T-162 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To evaluate lung SBRT proton plan robustness to daily setup and anatomy variations using different planning strategies.

Methods: Six lung SBRT patients treated using photon techniques were retrospectively analyzed. The photon plans were generated to cover the planning target volume (PTV), which is a 5 mm expansion to the internal target volume (ITV).Pencil beam scanning (PBS) technique with 2-3 field arrangement was used. For each patient, three planning strategies were applied to generate proton plans: 1) to cover the same PTV as in the photon plan 2) to cover the field specific target (5mm setup and 4% range uncertainty expansion from ITV), 3) to cover ITV considering 5mm setup and 4% range uncertainty using robust optimization. Both multi-field optimization (MFO) and single field optimization (SFO) were used. Daily anatomical and setup variations were estimated using CBCTs for each treatment. The planned doses were recalculated on the planning CT mapped to the daily CBCT through deformable registration to generate the accumulative dose. Dosimetric characteristics of all proton plans as well as original photon plans were assessed for plan robustness to daily anatomical and setup variations.

Results: Five millimeter uniform PTV expansion ensured 99% ITV coverage by prescription dose (PD) for photon plans; but only 95% and 96% ITV coverage by PD using MFO and SFO, respectively. Field specific target expansion using SFO ensured 99% ITV coverage by PD; but resulted in higher OAR doses. Robust optimization using both MFO and SFO ensured 99% ITV coverage by PD and resulted in better OAR dose sparing compared to those using the field specific target expansion technique.

Conclusion: The PTV expansion used for photon plans is not sufficient for proton plan design. The MFO technique with robust optimization generates more robust lung SBRT plan that ensures sufficient ITV coverage.

Funding Support, Disclosures, and Conflict of Interest: The funding is partially supported by Varian Reserach Funding

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