A novel respiratory surrogate system with table motion correction and visual feedback for computed tomography

Background and purpose

Managing respiratory motion is crucial for computed tomography (CT) in radiotherapy. Clinical surrogate systems and visual coaching can exhibit inaccuracies due to table motion or sag, limiting effectiveness in deep inspiration breath-hold (DIBH) CT and four-dimensional CT (4DCT). This study evaluated a motion-corrected novel surrogate and feedback system to improve DIBH and 4DCT breathing quality.

Materials and methods

The feedback system was evaluated in phantom tests for table sag compensation under incremental loads (up to 104 kg). For patients, DIBH plateau stability metrics (n = 2) and baseline shifts in 4DCT (n = 3) were assessed. In a volunteer study (n = 10), audio and visual feedback were compared in DIBH and 4DCT scenarios, assessing breath-hold stability and breathing regularity, respectively.

Results

In phantom measurements, the impact of table sag on the breathing signal was effectively reduced at maximum load, with baseline shifts limited to −0.2 mm, compared to up to −5 mm in clinical systems. In patients, the system improved DIBH signal stability, as reflected in the plateau drift (−0.2 mm/s vs. −0.8 mm/s), and substantially reduced baseline shifts in 4DCT (−0.2 ± 0.2 mm) when compared to clinical systems (−1.7 ± 0.3 mm). Volunteer tests demonstrated improved DIBH reproducibility with visual feedback (standard deviation: 0.5 mm vs. 1.1 mm with audio feedback). In 4DCT scenarios, visual feedback unified irregular breathers but offered no consistent improvement over audio guidance.

Conclusion

The novel system compensated for table motion in phantom, patient, and volunteer measurements. In feedback scenarios, it performed well in DIBH, while its performance in 4DCT requires further optimization.