Quantifying the influence of radiation therapy on functional shoulder health indicators in breast cancer patients: An exploratory study

Introduction: Radiotherapy is a highly effective treatment for breast cancer, but it is also associated with several complications that can impact quality of life and survivorship, including arm function. This study assessed the influence of radiation therapy on shoulder health indicators of breast cancer patients during their treatment period. Methods: Fourteen breast cancer patients undergoing radiation therapy participated. Shoulder health indicators were assessed at the baseline, midpoint, and endpoint of radiation treatment. The indicators included shoulder muscle activations, arm circumference, shoulder complex range of motion, and arm strength. Repeated measures ANOVAs followed by post-hoc Tukey-Kramer tests were used to identify differences in shoulder indicators between levels (p < 0.05). A multiple linear regression model was created for each dependent measurement including radiation dose and fractions as predictor variables. Results: The activation of the teres major and latissimus dorsi muscles decreased in most of the evaluated movements. Additionally, mean shoulder abduction decreased by 11 deg, and negative correlations existed between shoulder abduction range of motion and radiation dose, and between shoulder abduction strength and radiation fractions. The observed changes may relate to post-treatment inflammation, and lingering effects of radiation on shoulder health indicators may take longer to manifest, hindering identification within the treatment window.