Effects on Lung Tissue After Breast Cancer Radiation: Comparing Photon and Proton Therapies

Shruti Siva Kumar; Julie A Bradley; Nancy P Mendenhall; Raymond B Mailhot Vega; Eric D Brooks; Paul G Okunieff; Fantine Giap; Teena Burchianti; Karen Daily; Coy D Heldermon; Zhanna Galochkina; Ji-Hyun Lee; Steven Swarts; Walter G O'Dell

doi:10.1016/j.ijpt.2024.02.001

Effects on Lung Tissue After Breast Cancer Radiation: Comparing Photon and Proton Therapies

Int J Part Ther. 2024 Apr 22:11:100006. doi: 10.1016/j.ijpt.2024.02.001. eCollection 2024 Mar.

Affiliations

¹ Alcon Research Ltd, Irvine, CA, USA.
² Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, USA.
³ University of Florida Health Proton Therapy Institute, Jacksonville, FL, USA.
⁴ Division of Hematology & Oncology, Department of Medicine, University of Florida College of Medicine, Gainesville, FL, USA.
⁵ Division of Quantitative Sciences, University of Florida Health Cancer Center, Gainesville, FL, USA.
⁶ Department of Biostatistics, University of Florida College of Health Profession & Public Health and College of Medicine, Gainesville, FL, USA.

Abstract

Purpose: In breast cancer, improved treatment approaches that reduce injury to lung tissue and early diagnosis and intervention for lung toxicity are increasingly important in survivorship. The aims of this study are to (1) compare lung tissue radiographic changes in women treated with conventional photon radiation therapy and those treated with proton therapy (PT), (2) assess the volume of lung irradiated to 5 Gy (V5) and 20 Gy (V20) by treatment modality, and (3) quantify the effects of V5, V20, time, and smoking history on the severity of tissue radiographic changes.

Patients and methods: A prospective observational study of female breast cancer patients was conducted to monitor postradiation subclinical lung tissue radiographic changes. Repeated follow-up x-ray computed tomography scans were acquired through 2 years after treatment. In-house software was used to quantify an internally normalized measure of pulmonary tissue density change over time from the computed tomography scans, emphasizing the 6- and 12-month time points.

Results: Compared with photon therapy, PT was associated with significantly lower lung V5 and V20. Lung V20 (but not V5) correlated significantly with increased subclinical lung tissue radiographic changes 6 months after treatment, and neither correlated with lung effects at 12 months. Significant lung tissue density changes were present in photon therapy patients at 6 and 12 months but not in PT patients. Significant lung tissue density change persisted at 12 months in ever-smokers but not in never-smokers.

Conclusion: Patients treated with PT had significantly lower radiation exposure to the lungs and less statistically significant tissue density change, suggesting decreased injury and/or improved recovery compared to photon therapy. These findings motivate additional studies in larger, randomized, and more diverse cohorts to further investigate the contributions of treatment modality and smoking regarding the short- and long-term radiographic effects of radiation on lung tissue.

Keywords: Breast cancer; Chest CT; Lung radiation damage.