Design and validation of a real-breath-sound-guided laser system for improved respiratory regularity in radiotherapy

Abstract

Robust respiratory motion management is crucial in radiotherapy to consider tumor movement throughout the breathing cycle. The widely used gating techniques exhibit limitations such as compromised targeting accuracy and prolonged treatment times. In this study, we developed and evaluated a laser-distance-sensor-based respiratory-training prototype designed to operate seamlessly in a standard gating environment. This study aimed to improve breathing regularity in radiotherapy patients using a new audio-guided respiratory-training approach that utilizes real breath sounds and a highly accurate laser displacement sensor. The system comprised two modules: a laser-based respiratory-monitoring component and an audio-guiding component. The accuracy and reproducibility of the laser module were tested using Vernier calipers and a motion phantom programmed with various sinusoidal and patient-like respiratory patterns. Measurements were obtained across a wide range of amplitudes (2.5-7.5 mm), cycle lengths (1.0-5.0 s), and environmental setups (different angles, lighting conditions, and surface reflectivity). Subsequently, volunteer tests were conducted to assess the clinical feasibility of the audio-guided training by comparing the breathing stability before and after training. Across all tested distances (65-135 mm), the laser sensor showed an average deviation of +/- 0.04 mm from the reference, with standard deviations consistently below 0.03 mm. In motion phantom studies, the measured amplitudes and cycle lengths closely matched the input values, achieving correlation coefficients of >= 0.99 even under irregular respiratory patterns. The system performance remained robust to angle deviations (+/- 15 degrees), low lighting, and surface reflectivity changes. In volunteer tests, the standard deviation of breathing cycles decreased substantially after training (from 0.82 to 0.26 s on average), indicating enhanced breathing regularity and user control. The cost-effective, laser-based respiratory-training system demonstrated high measurement accuracy, stable performance, and clinically relevant improvements in breathing consistency, indicating its potential for integration with laser gating setups, particularly in shell-based radiotherapy treatments.