Alternating inspiration and expiration breath-hold techniques spare the chest wall during stereotactic body radiotherapy for peripheral lung malignancies

Background: Stereotactic body radiotherapy (SBRT) for peripheral lung cancer and metastasis increases the chest wall toxicity due to its proximity to the high dose region of the PTV. Herein, we propose a solution of alternating breath-hold on half of the treatment course to spare the chest wall without compromising the PTV coverage. Methods: Twenty patients with lung lesions adjacent to the chest wall were enrolled in this study and received respiratory coaching one week in advance. Simulation CT scanning was carried out under both end-expiration breath-hold (EEBH) and deep inspiration breath-hold (DIBH), and coplanar volumetric modulated arc therapy (VMAT) plans were created on both of the two series of breath-hold CT images. Dosimetric parameters of the chest wall (V30, V40, Dmax, D0.1cc, D1cc, and D5cc) and bilateral lungs (V5, V10, V20, and MLD) were compared among plans under EEBH alone, DIBH alone, and EEBH plus DIBH. Meanwhile, the correlation between tumor location and the outcome of chest wall sparing was quantitatively evaluated. Paired t test was applied and differences with P < 0.05 were considered statistically significant. Results: Compared to EEBH and DIBH plans, alternating breath-hold techniques result in reduction rates of 47.7% and 54.5% (V30), 56.7% and 65.4% (V40), 2.0% and 3.9% (Dmax), 6.2% and 7.6% (D0.1cc), 16.0% and 15.2% (D1cc), 14.6% and 19.1% (D5cc), respectively. Slight increase in lung V5 (< 6%), and no significant differences can be observed in lung V10, V20, and MLD. Tumor displacement with combined breath-hold appears to be greater in the lower lobes (SI/d: 1.17) than in the upper and middle lobe (SI/d: 0.18), allowing for better chest wall sparing nearly 100% in high dose volumes and 40% in high point doses. Conclusions: Alternating deep inspiration and end-expiration breath-hold techniques can significantly spare the immediately adjacent chest wall without compromising PTV coverage in SBRT of peripheral lung malignancies. Furthermore, patients with tumors in the lower lobes can obtain the most beneficial dose reduction than in the upper and middle lobes.