KEY POINTS
- Model-based risk analysis of 1,690 Korean early-stage breast cancer patients treated with clinically delivered breast radiotherapy plans.
- Four cohorts were compared: stereotactic partial breast irradiation (806), three-dimensional conformal partial breast irradiation (43), volumetric modulated arc therapy whole breast irradiation (456), and three-dimensional conformal whole breast irradiation (385).
- Mean lung dose increased across groups: 1.37 Gy, 1.52 Gy, 1.86 Gy, and 2.60 Gy, respectively; equivalent dose in 2-Gy fractions was 0.90 Gy, 1.00 Gy, 1.26 Gy, and 1.67 Gy.
- In the primary covariate-controlled RadRAT model, excess lifetime secondary lung cancer risk was 2,003, 1,931, 2,843, and 3,738 cases per 100,000 patients, respectively.
- Projected lifetime relative risk ranged from 1.54 to 2.05, raising baseline lifetime lung cancer risk from 3.6% to 5.5–5.6% with partial breast irradiation and 6.4–7.3% with whole breast irradiation.
CLINICAL TAKEAWAY
This study supports considering secondary lung cancer risk as one additional factor when choosing between partial and whole breast irradiation in appropriately selected low-risk breast cancer patients. The strongest signal is about treatment volume and lung dose, not a simple “technique good or bad” ranking. The evidence remains model-based rather than observed cancer-incidence data, with limitations including RadRAT assumptions, no explicit modeling of radiation-smoking synergy, and a small three-dimensional conformal partial breast irradiation cohort.
SOURCE
International Journal of Radiation Oncology, Biology, Physics