Can physical parameters from radiation simulation scan with deep inspiratory breath hold predict magnitude of heart dose reduction?

Introduction: Deep inspiratory breath hold is one of the techniques for reducing the heart doses for left breast cancers. This study was conducted to confirm use of physical parameters from DIBH simulation CT scan like DIBH amplitude alongside several novel parameters to predict the heart dose reduction.

Materials and methods: Segmentation and planning of radiation to the left breast on the free breathing (FB) and DIBH simulation scan was performed for 50 left-sided breast cancer patients treated with DIBH technique. Physical parameters, namely DIBH amplitude, anterior sternal displacement, diaphragmatic excursion, ratio of lung volume (cc) in DIBH scan to lung volume in FB scan (cc), and delta heart volume in field (DHVIF), were extracted and were compared with magnitude of heart dose reduction (mean heart dose, V30Gy, and D5%).

Results: Forty-eight (96%) patients achieved reduction in the mean heart dose with DIBH technique, while all patients had reduction in V30Gy. The median reduction was 41%, 89.7%, and 63% in the mean dose, V30Gy, and D5%, respectively. While DIBH did not correlate with heart dose reduction, ratio of lung volumes and DHVIF showed a strong positive correlation with heart dose reduction (P < 0.05). Sternal displacement correlated weakly with heart dose reduction but strongly with DHVIF, demonstrating to be an indirect predictor.

Conclusions: Physical parameters like anterior sternal displacement, ratio of lung volumes of DIBH to FB, and possibly diaphragmatic movement can predict the dose reduction before the dose calculations by the physicist. These parameters can be used to construct a model to predict heart dose reduction.