mmWave Sensing for Detecting Movement Through Thermoplastic Masks During Radiation Therapy Treatment

TL;DR

This paper investigates the use of millimeter-wave sensing as a non-ionizing method to detect subtle patient movements through thermoplastic masks during radiation therapy, aiming to improve treatment accuracy.

Contribution

It characterizes the RF properties of thermoplastic masks in the 28-38 GHz range and demonstrates through-mask motion detection using mmWave signals in a controlled environment.

Findings

RF properties of thermoplastic masks characterized in 28-38 GHz range

Successful detection of subtle head and facial movements with mmWave signals

Foundation for real-time through-mask motion tracking in radiotherapy

Abstract

Precision in radiation therapy relies on immobilization systems that limit patient motion. Thermoplastic masks are commonly used for this purpose, but subtle voluntary and involuntary movements such as jaw shifts, deep breathing, or eye squinting may still compromise treatment accuracy. Existing motion tracking methods are limited: optical systems require a clear line of sight and only detect surface motion, while X-ray-based tracking introduces additional ionizing radiation. This study explores the use of low-power, non-ionizing millimeter-wave (mmWave) sensing for through-mask motion detection. We characterize the RF properties of thermoplastic mask material in the 28-38 GHz range and perform motion detection using a 1 GHz bandwidth centered at 28 GHz. We use a frequency-domain system with horn antennas in a custom-built anechoic chamber to capture changes in the amplitude and phase of transmitted RF waves in response to subtle head and facial movements. These findings lay groundwork for future real-time through-mask motion tracking and future integration with multi-antenna systems and machine learning for error correction during radiotherapy.