Session Item

An electronic portal image device (EPID) based system for real-time monitoring of breath-hold quality during deep inspiration breath-hold (DIBH) breast cancer treatments has been developed [1]. Live EPID-based Inspiration Level Assessment (LEILA) uses internal surrogates, the position of the bony chest wall and the patient’s skin, to assess the alignment of anatomy with the treatment beam. LEILA is currently being tested with patients. Its ability to measure at multiple locations has been utilized to identify instances where the patient arched their back instead of taking a deep breath-hold, which is known cause of lower DIBH quality. [2]

LEILA analyses portal MV images of breast tangents and measures the lung depth (LD) and the distance from the skin to posterior field edge (skin distance, SD) at 3 user-selected locations as shown in Figure 1A. It displays these six parameters in real time and tracks them over time. In this study, breathing and breath-hold of the patients during RT were monitored and directed with the Varian’s RPM or C-RAD’s Catalyst+ systems. In both situations, the breathing window, the allowed motion, was 5 mm.  

The plots of LDs during “Breath-hold 2” in Figure 1B show typical time traces of the 3 LD parameters (superior, midline, and inferior) seen during the DIBH treatments: the time dependences of the superior, midline, and inferior LDs are changing in the same direction. For two patients on the study (Patient A and Patient B) there were instances when the superior LD was decreasing while the midline and inferior LDs were increasing (“Breath-hold 1” in Fig. 1B, and at the start of beam 3 and beam 4 in Fig. 1C). These observations likely indicate arching of the back. For Patient A, the observation was made during 1 beam of 48 beams tested with LEILA. For Patient B, the observation was made for 2 of 36 beams tested. While the amplitude of the changes of the 3 LD parameters during these instances was small, it is clear enough to implement a simple automated trend check during real-time monitoring with LEILA, which alerts the operator of back arching.

Real-time assessment of the quality of DIBH via the internal surrogates, the LD and SD parameters at multiple levels in the radiation field, can help identify situations where the patient arches their back instead of taking a sufficiently deep breath-hold in DIBH breast cancer treatments.

References

1. Vasina E.N., Greer P., Thwaites D., Kron T., Lehmann J., A system for real-time monitoring of breath-hold via assessment of internal anatomy in tangential breast radiotherapy. Accepted to JACMP.

2. Bossuyt E, Weytjens R, Nevens D, De Vos S, Verellen D. Evaluation of automated pre-treatment and transit in-vivo dosimetry in radiotherapy using empirically determined parameters. phiRO. 2020 Oct 1;16:113-29.

Acknowledgements

This work was supported by NHMRC grant 1147533.