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

Y Lin

Y Lin1*, M Fang1 , M Zhu2 , Q Wu1 , C Willett1 , F Yin1 , (1) Department of Radiation Oncology, Duke University Medical Center, Durham, NC, (2) Department of Radiation Oncology, Maryland Proton Treatment Center, University of Maryland School of Medicine, Baltimore, MD


SU-I-GPD-T-177 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

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

Methods: Five liver SBRT patients treated using photon techniques were retrospectively analyzed. The photon plans were generated to cover the PTV (7mm expansion to ITV).For each patient, three proton planning strategies using pencil beam scanning techniques were used: 1) to cover the same PTV as in photon plan 2) to cover the field specific target (7mm setup and 4% range uncertainty expansion from ITV), 3) to cover ITV considering 7mm setup and 4% range uncertainty using robust optimization. Both multi-field optimization (MFO) and single field optimization (SFO) were used. The daily setup and anatomy variations were characterized using CBCTs acquired before radiation treatment. The planned doses were recalculated on planning CT mapped to daily CBCT through deformable registration and dosimetric characteristics of all proton plans and original photon plans were assessed for plan robustness to daily anatomical and setup variations.

Results: The proton plans showed significantly lower OAR doses compared to photon plans due to the superior physical characteristic of proton beams. The SFO technique ensured 99% ITV coverage by prescription dose (PD) for all proton plans over the course of treatment. In the meantime, the MFO technique with robust optimization showed not only 100% ITV coverage by PD but also the lowest OAR doses (V20 for kidney, mean liver dose, etc) among all proton plans.

Conclusion: The proton plans show superior OARs sparing compared to photon plans. This is important for liver SBRT since the effective liver volume irradiated is highly associated with toxicity and limits the dose that can be prescribed to the target. The MFO technique with robust optimization is favorable in generating robust liver SBRT plan that ensures sufficient ITV coverage and superior OAR sparing.

Funding Support, Disclosures, and Conflict of Interest: The reserach is supported byt Varian Reserach Grant

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