Stability and reproducibility of 6013 deep inspiration breath-holds in left-sided breast cancer

Abstract

Purpose: Patients with left-sided breast cancer frequently receive deep inspiration breath-hold (DIBH) radiotherapy to reduce the risk of cardiac side effects. The aim of the present study was to analyze intra-breath-hold stability and inter-fraction breath-hold reproducibility in clinical practice.

Material and methods: Overall, we analyzed 103 patients receiving left-sided breast cancer radiotherapy using a surface-guided DIBH technique. During each treatment session the vertical motion of the patient was continuously measured by a surface guided radiation therapy (SGRT) system and automated gating control (beam on/off) was performed using an audio-visual patient feedback system. Dose delivery was automatically triggered when the tracking point was within a predefined gating window. Intra-breath-hold stability and inter-fraction reproducibility across all fractions of the entire treatment course were analyzed per patient.

Results: In the present series, 6013 breath-holds during beam-on time were analyzed. The mean amplitude of the gating window from the baseline breathing curve (maximum expiration during free breathing) was 15.8 mm (95%-confidence interval: [8.5-30.6] mm) and had a width of 3.5 mm (95%-CI: [2-4.3] mm). As a measure of intra-breath-hold stability, the median standard deviation of the breath-hold level during DIBH was 0.3 mm (95%-CI: [0.1-0.9] mm). Similarly, the median absolute intra-breath-hold linear amplitude deviation was 0.4 mm (95%-CI: [0.01-2.1] mm). Reproducibility testing showed good inter-fractional reliability, as the maximum difference in the breathing amplitudes in all patients and all fractions were 1.3 mm on average (95%-CI: [0.5-2.6] mm).

Conclusion: The clinical integration of an optical surface scanner enables a stable and reliable DIBH treatment delivery during SGRT for left-sided breast cancer in clinical routine.

Keywords: Breast cancer; DIBH; Inter-fraction; Intra-breath-hold; Optical surface scanner; Reproducibility; Stability; Surface guided radiation therapy.

Fig. 1

Graphical demonstration of the c4D-Tool; the red point on the patients surface is the reference point for tracking the vertical amplitude during breath-hold; the lower part of the screenshot shows an amplitude over time-plot

Fig. 2

Time plot showing the vertical breathing curve amplitude over time; dashed red lines are showing the lower and upper limit of the gating window

Fig. 3

One deep inspiration breath-hold cycle plot showing the vertical deviation in millimeters over time (blue); the green line is a linear fit plot of the blue signal (example of the linear function by linear fit: y = 0.0165•time+ 17.69); dashed red lines are showing the lower and upper limit of the gating window

Fig. 4

a Box plots of breathing amplitudes during breath-hold for every patient including all breath-holds sorted by the median value, b histogram of the breathing amplitudes (n = 103 patients, 6013 breath-holds)

Fig. 5

a Box plots of standard deviation of the breath-hold levels for every patient. b histogram of the standard deviations. c Box plots of the linear fit amplitude in millimeters inside the gating window during breath-hold for every patient based on linear fit model. d histogram of the linear fit amplitudes (n = 103 patients, 6013 breath-holds)