S McCarthy*, M Bernard, W St Clair, M Kudrimoti, D Pokhrel, University of Kentucky, Lexington, KY

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  S McCarthy

TU-F115-IePD-F7-3 (Tuesday, 7/12/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 7

Purpose: SBRT treatment of central/ultra-central non-small-cell lung cancers (NSCLC) in the “no-fly-zone”, located 2 cm around the proximal bronchial tree (PBT), demonstrates a higher risk of complications, and reported local failure from under dosing tumors. Herein, we demonstrate the plan quality and delivery efficiency of volumetric modulated arc therapy (VMAT) with the Halcyon Linac for centrally-located lung SBRT.

Methods: Fourteen centrally-located NSCLC patients who underwent non-coplanar 6MV-FFF partial-arcs VMAT lung SBRT on C-arm TrueBeam using AcurosXB algorithm were selected. Prescribed dose was 50 Gy in 5 fractions every other day per NRG-RTOG-0813. TrueBeam plans were re-optimized for Halcyon (coplanar, 6MV-FFF) utilizing 4 full-arcs with contralateral lung avoidance sectors. The two plans were compared via their protocol compliance, target conformity, gradient index, and dose to critical organs including surrounding lungs. Treatment delivery parameters, and beam-on time, were reported.

Results: All Halcyon plans met RTOG-0813 requirements and provided statistically similar clinically delivered TrueBeam plans for dose conformity, gradient indices, and dose-to-critical-organs (all, p>0.05). Halcyon plans achieved a higher mean target dose by 1.0 Gy,(p=0.019), systematically lower MLD by 0.2 Gy(p=0.761), and maximum dose to PBT by 2.0 Gy(p=0.757), respectively. Plan complexity slightly increased, noted by the average increase of total monitor units (173, p=0.538) and beam-on time (1.36 min, p<0.001). Estimated overall treatment time reduced by 2.64 min (p<0.001), on average and can be delivered in 15 min slot. Portal dosimetry QA demonstrated a pass rate of 99.8% for clinical gamma passing criteria of 2%/2 mm. Independent Monte Carlo calculation showed agreement to treatment planning system within 1.5%.

Conclusion: SBRT treatment of centrally-located NSCLC on Halcyon is a feasible option that provides excellent plan quality and shortened treatment time, while remaining dosimetrically similar to clinically delivered non-coplanar TrueBeam plans. For select centrally-located NSCLC, Halcyon is an efficient and effective SBRT treatment modality.

Keywords

Treatment Planning, Intensity Modulation, Inverse Planning

Taxonomy

TH- External Beam- Photons: extracranial stereotactic/SBRT

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