Effects of breath-hold reproducibility on proton and photon lung cancer stereotactic body radiotherapy

The article investigates how variations in breath-hold reproducibility influence dose delivery in stereotactic body radiotherapy (SBRT) for lung cancer, comparing proton and photon treatment techniques. Breath-hold methods, such as deep-inspiration breath-hold (DIBH), are commonly used to reduce tumor motion and spare surrounding healthy tissues. However, small differences in repeated breath-hold positions may affect dose distribution, particularly in proton therapy, which is more sensitive to anatomical and density changes.

In this study, the authors analyzed imaging data from lung cancer patients treated under breath-hold conditions. They simulated inter-breath-hold variability by incorporating measured positional and anatomical differences into treatment plans for both proton and photon SBRT. Dosimetric parameters, including target coverage and doses to organs at risk (OARs), were compared under varying levels of reproducibility.

The results showed that photon SBRT was relatively robust to moderate breath-hold variations, with limited impact on target coverage and OAR doses. In contrast, proton SBRT demonstrated greater sensitivity to anatomical changes, leading in some cases to reduced target coverage or increased dose heterogeneity. This increased sensitivity was attributed to the finite proton range and its dependence on tissue density along the beam path. Nevertheless, when breath-hold reproducibility was high, proton therapy maintained its dosimetric advantages in sparing normal tissues.

The study concludes that breath-hold consistency is critical for safe and effective proton SBRT in lung cancer. While proton therapy offers superior normal tissue sparing, its successful implementation requires stringent motion management and reproducibility protocols to ensure robust and reliable dose delivery.

Published by Physics and Imaging in Radiation Oncology 37 (2026) 100926
DOI: 10.1016/j.phro.2026.100926