Dosimetric Comparison of Deep Inspiration Breath Hold and Free Breathing Treatment Techniques for Left-sided Breast Cancer Using 3-Dimensional Surface Tracking

Abstract

While radiation therapy has been shown to increase local control and overall survival for breast cancer, cardiac toxicity remains a concern. Morbidity and mortality have been shown to increase proportionally to the mean heart dose. Deep inspiration breath hold (DIBH) can reduce heart dose compared to free-breathing (FB) delivery by increasing the distance from the heart to the chest wall, especially in left-sided breast cancer. DIBH requires monitoring of patients' respiratory motion. We report our experience with DIBH in left breast and chest-wall irradiation using 3D optical surface tracking. Thirty patients were treated using DIBH with a surface tracking system that provides a real time 3D surface image of the patient. This image is registered with the patient's body contour to facilitate setup and provide real time position offsets. Treatment plans were created on FB and DIBH images to compare doses to the heart and lungs. The distance between the heart and chest wall was measured at the 7th thoracic vertebra at 11 cm anterior to the spinal canal. Unpaired t-test was used to compare means and mean differences in heart and lung doses between plans. Correlation coefficients were derived for anatomic variances, such as heart and chest wall separation as well as heart and lung volumes. A comparison of DIBH and FB plans showed a decrease in mean and maximum heart doses in all patients. Individual patients’ mean heart doses decreased by an average of 1.12 Gy, and the average mean heart dose for DIBH plans was significantly lower than for FB plans (1.02 vs 2.12 Gy; P<0.0001). When lumpectomy and mastectomy patients were separated, this statistical significance was maintained in each group (P<0.0001 and P = 0.0233, respectively). Maximum heart dose decreased by an average of 11.88 Gy and was significantly lower in DIBH plans versus FB plans (28.33 vs 43.7 Gy; P = 0.0001). The average difference in heart to chest-wall separation between DIBH and FB images was 2.41 cm. This difference correlated positively with mean (R = 0.24) and maximum (R = 0.51) heart doses. While a trend towards improved left lung V20 was noted (14.04 vs 15.78%; P = 0.057), a significant difference was noted only for intact breast patients treated with opposed tangents alone (12.25 vs 15.06 Gy; P = 0.0257) versus plans with additional regional nodal radiation fields. Heart volume did not correlate with any measurements. However, DIBH left lung volume and the measured increase in volume on inspiration inversely correlated with maximum heart dose (R = 0.39) and left lung V20 (R = 0.32). DIBH with 3D surface tracking can significantly benefit patients with left sided disease by limiting the mean and maximum heart dose. In addition, DIBH showed a trend in improving lung V20 in intact breast patients treated with tangents alone. DIBH appears to be a viable option to reduce heart dose for left sided breast cancer patients and thus potentially reduce long-term complications without prolonging treatment delivery.