Mechanically-assisted non-invasive ventilation: A step forward to modulate and to improve the reproducibility of breathing-related motion in radiation therapy.

BACKGROUND AND PURPOSE

When using highly conformal radiotherapy techniques, a stabilized breathing pattern could greatly benefit the treatment of mobile tumours. Therefore, we assessed the feasibility of Mechanically-assisted non-invasive ventilation (MANIV) on unsedated volunteers, and its ability to stabilize and modulate the breathing pattern over time.

MATERIALS AND METHODS

Twelve healthy volunteers underwent 2 sessions of dynamic MRI under 4 ventilation modes: spontaneous breathing (SP), volume-controlled mode (VC) that imposes regular breathing in physiologic conditions, shallow-controlled mode (SH) that intends to lower amplitudes while increasing the breathing rate, and slow-controlled mode (SL) that mimics end-inspiratory breath-holds. The last 3 modes were achieved under respirator without sedation. The motion of the diaphragm was tracked along the breathing cycles on MRI images and expressed in position, breathing amplitude, and breathing period for intra- and inter-session analyses. In addition, end-inspiratory breath-hold duration and position stability were analysed during the SL mode.

RESULTS

MANIV was well-tolerated by all volunteers, without adverse event. The MRI environment led to more discomfort than MANIV itself. Compared to SP, VC and SH modes improved the inter-session reproducibility of the amplitude (by 43% and 47% respectively) and significantly stabilized the intra- and inter-session breathing rate (p < 0.001). Compared to VC, SH mode significantly reduced the intra-session mean amplitude (36%) (p < 0.002), its variability (42%) (p < 0.001), and the intra-session baseline shift (26%) (p < 0.001). The SL mode achieved end-inspiratory plateaus lasting more than 10 s.

CONCLUSION

MANIV offers exciting perspectives for motion management. It improves its intra- and inter-session reproducibility and should facilitate respiratory tracking, gating or margin techniques for both photon and proton treatments.