Session Item

Deep inspiration breath-hold radiotherapy has become a standard of care for left-sided breast cancer patients. We used a surface guided optical system to quantify the reproducibility and stability of spirometer-guided breath-hold breast treatments.

Five consecutive left-sided breast cancer patients were treated in breath-hold using the Active Breathing Coordinator spirometer (ABC). Patients were treated with an hybrid-IMRT technique and simultaneous integrated boost to surgical cavity. An optical surface-guided scanning system device (AlignRT) was used to continuously monitor the left breast during treatment. The inter-fraction, intra-fraction and intra-breath-hold motion was quantified in the anterior-posterior (VER), superior-inferior (LNG) and lateral-lateral (LAT) directions. The DIBH intra-breath-hold stability (S) was defined as the linear amplitude deviation during a DIBH maneuver (and calculated as the gradient of the regression straight line multiplied with the DIBH-time interval). For each breath-hold sequence during a treatment fraction, the intra-fraction reproducibility (R) was defined as the maximum difference between different DIBH levels. The inter-fraction reproducibility (T) was determined as the difference between the mean breath-hold level per fraction and the mean breath-hold level during the first fraction. Correlations between ABC tidal volume and surface imaging deviations were investigated.

Each treatment fraction was completed using 4-6 breath-holds. 75 treatment fractions and 625 breath-holds during beam-on time were analyzed. Overall ABC intra-session lung volume variation was <1.5%. With regard to intra-breath-hold stability, the median linear deviations S were 1.3 mm (95%-CI: [0.0–2.2] mm), 2.4 mm (95%-CI: [0.3–6.7] mm) and 0.8 mm (95%-CI: [0.0–1.7] mm) ) in the VER, LNG and LAT directions, respectively. Results for the LNG direction indicated that the drift over time during breath-hold are not negligible, up to 9 mm even at constant inspired volumes. With regard to intra-fraction reproducibility, the averaged results reported R median values of 1.3 mm (95%-CI: [0.0–1.9] mm), 1.4 mm (95%-CI: [0.0–2.9] mm) and 0.8 mm (95%-CI: [0.0–1.3] mm) in the VER, LNG and LAT directions, respectively. Median inter-fractional reproducibility was found 0.0 mm (95%-CI: [-0.6–0.6] mm), -0.3 mm (95%-CI: [-1.4–0,2] mm) and 0.0 mm (95%-CI: [-0.2–0,2] mm) in the VER, LNG and LAT directions, respectively. No correlations were found between ABC breath-hold levels and surface monitoring deviations in all directions. Figure shows an example of the ABC spirometer (upper) and AlignRT time trajectories along VER and LNG  directions (lower) for three representative breath-holds.  

Despite the use of spirometer-controlled lung volume, breast immobilization may not be stable and reproducible as expected. The integration of spirometry with an optical surface-guided guidance system may increase surface position reproducibility during repeated DIBHs.