Ming-Hsiang Liou, Tsair-Fwu Lee, Pei-Ju Chao, Hsiao-Yi Lee and Yu-Jie Huang
Division of Radiation Oncology, Yuan's General Hospital, Taiwan
Methods: In total, 120 patients with breast cancer were analyzed. All participants were treated with IMRT or hybrid IMRT. The final endpoint was defined as those who with symptomatic pneumonitis combined with computerized tomography (CT) measured density changes grade ≥1. The risk factors for a multivariate logistic regression normal tissue complication probability (NTCP) model of SRP were determined using the least absolute shrinkage and selection operator (LASSO) technique.
Results: Three risk factors were selected using LASSO: the percentage of the ipsilateral lung volume that received more than 20-Gy (IV20), age, and body mass index (BMI). Our analyses indicate that the risk of SPR following IMRT/hybrid IMRT in elderly or low-BMI breast cancer patients increases when the percentage of the ipsilateral lung volume receiving more than 20-Gy is controlled below 30%.
Conclusions: We suggest to define a dose-volume percentage constraint of IV20Gy < 30% for the irradiated ipsilateral lung in radiation therapy treatment planning to maintain the incidence of SPR below 10%, and pay attention to the sequelae especially in elderly or low-BMI breast cancer patients.
Key words: Symptomatic radiation pneumonitis, LASSO, NTCP, multivariable logistic regression.