AL Van Slyke*, M Mashayekhi, JK Molitoris, WF Regine, B Yi, B Zhang, S Chen, University of Maryland School of Medicine, Baltimore, MD

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TU-G-BRA-3 (Tuesday, 7/12/2022) 1:45 PM - 2:45 PM [Eastern Time (GMT-4)]

Ballroom A

Purpose: LATTICE radiation therapy (LRT) is an extension of conventional GRID therapy that delivers a high dose (>12Gy) to spherical vertices and maintains a low dose (3Gy) between vertices. Respiration-induced motion may blur this dose distribution, reducing the volume receiving high dose. This study investigated the effect of respiration-induced motion on the dose distribution for patients receiving LRT to the pelvis, thorax, and abdomen.

Methods: To estimate the effect of respiration-induced motion on the dose distribution in LRT, a retrospective study was performed on 9 patients who had received LRT. These treatment plans consisted of 1cm diameter spherical vertices prescribed to 12Gy, spaced 2cm apart throughout the tumor, with 3Gy covering >95% of the GTV. The plans were delivered using VMAT with 5-8 arcs. Breathing motion was simulated by shifting the isocenter in 1.3 or 2.5mm steps along the superior-inferior axis and recalculating the dose. 5-8 symmetric steps were combined to create plans simulating 0.5, 1, 1.5, and 2cm total motion. V12Gy (Δ%), dose peak-to-valley ratio (Δ%), GTV V3Gy (%), and GTV (Δ%) mean dose were used as metrics to evaluate the dose distribution.

Results: The volume of vertices receiving 12Gy exhibited the most significant change as a result of motion, being reduced to 52.0±10.2% and 5.9±7.9% of the treated value at 1 and 2cm displacement, respectively (mean±std). Dose peak-to-valley ratio decreased by 8.5±3.7% and 20.8±6.9% of the clinical plan at 1 and 2cm. GTV mean dose decreased by 0.7±0.3% of the clinical plan and V3Gy (%) increased from 97.0±0.8% to 97.9±0.7% at 2cm.

Conclusion: The low dose metrics were not significantly impacted by superior-inferior motion up to 2cm. However, the high dose to vertices (V12Gy) and peak-to-valley ratio was reduced due to respiratory-induced motion. Motion management should be considered for LRT treatments of the pelvis, thorax, and abdomen.

Keywords

Patient Movement, Radiation Therapy

Taxonomy

TH- External Beam- Photons: Development (new technology and techniques)

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