Adaptive motion mapping in pancreatic SBRT patients using Fourier transforms

TL;DR

This study introduces a Fourier transform-based metric called Spectral Coherence to predict and adapt to pancreatic tumor motion during SBRT, improving dose coverage by tailoring treatment margins to individual respiratory patterns.

Contribution

The paper presents a novel Fourier-based method for assessing and adapting to daily pancreatic tumor motion, enhancing the precision of SBRT treatments.

Findings

Daily motion exceeded pre-treatment predictions by 2.3-3.5 mm.

Spectral Coherence correlated with motion deviations and dose coverage.

Adaptive margins based on SC improved target dose metrics.

Abstract

Recent studies suggest that 4DCT is unable to accurately measure respiratory-induced pancreatic tumor motion. In this work, we assessed the daily motion of pancreatic tumors treated with SBRT, and developed adaptive strategies to predict and account for this motion. The daily motion trajectory of pancreatic tumors during CBCT acquisition was calculated using a model which reconstructs the instantaneous 3D position in each 2D CBCT projection image. We developed a metric (termed "Spectral Coherence," SC) based on the Fourier frequency spectrum of motion in the SI direction, and analyzed the ability of SC to predict motion-based errors and classify patients according to motion characteristics. The amplitude of daily motion exceeded the predictions of pre-treatment 4DCT imaging by an average of 3.0 mm, 2.3 mm, and 3.5 mm in the AP, LR, and SI directions. SC was correlated with daily motion differences and tumor dose coverage. In a simulated adaptive protocol, target margins were adjusted based on SC, resulting in significant increases in mean target D95, D99, and minimum dose. Our Fourier-based approach differentiates between consistent and inconsistent motion characteristics of respiration and correlates with daily motion deviations from pre-treatment 4DCT. The feasibility of an SC-based adaptive protocol was demonstrated, and this patient-specific respiratory information was used to improve target dosimetry by expanding coverage in inconsistent breathers while shrinking treatment volumes in consistent breathers.