Lung Dose and Pneumonitis Risk Following Five‐Fraction Breast Radiotherapy
Kristin A. Ward, Matthew J. Case, Matthew Thomas, Sheela Hanasoge, Mylin A. Torres, Jolinta Y. Lin, Heather G. Gatcombe, Rohini K. Bhatia, Natalie A. Ridge, Karen D. Godette, David Yu, Reshma Jagsi, Sunil W. DuttaABSTRACT
Purpose
To evaluate associations between lung dose and symptomatic pneumonitis in five‐fraction breast radiotherapy and identify strategies to limit lung exposure.
Methods and Materials
We retrospectively analysed 224 consecutive patients with early‐stage breast cancer treated between 2020 and 2024 at a single institution using five‐fraction adjuvant radiotherapy, including whole‐breast radiotherapy (WBRT [ N = 157]: 26 Gy [5.2 Gy daily] or 28.5 Gy [5.7 Gy weekly]) and accelerated partial‐breast irradiation (APBI [ N = 67]: 30 Gy [6 Gy every other day]). Associations between lung dose‐volume parameters and symptomatic pneumonitis were examined, along with potential dose thresholds linked to increased risk.
Results
At a median follow‐up of 13 months, 8 patients (3.6%) developed symptomatic (grade ≥ 2) pneumonitis. Symptoms were mostly mild and self‐limited, with only one patient experiencing grade 3 pneumonitis. Pneumonitis risk showed a dose–response pattern: Each 1% increase in ipsilateral lung volume receiving 8 Gy, 10 Gy, and 20 Gy was associated with relative risk increases of 13%, 23%, and 33%, respectively (all p < 0.05). An exploratory threshold of V20Gy ≥ 7.5% identified a subgroup of patients at higher risk, with pneumonitis rates of 9.0% (7/78) above this threshold compared to 0.7% (1/146) for those below (AUC 0.79). In patients receiving WBRT, prone positioning reduced lung V20Gy. APBI was also associated with lower lung V20Gy (both p < 0.05).
Conclusion
Although mild and self‐limited, the risk of symptomatic pneumonitis progressively increased with higher fractional lung doses during five‐fraction breast radiotherapy. APBI or prone positioning for WBRT may help reduce intermediate‐to‐high lung dose volumes (such as V20Gy) and pneumonitis risk in eligible patients.