External Beam Accelerated Partial Breast Irradiation in Early Breast Cancer and the Risk for Radiogenic Pneumonitis

Area of Science:

• Oncology
• Radiotherapy
• Medical Physics

Background:

• Accelerated partial breast irradiation (APBI) is an alternative to whole breast irradiation (WBI) for early-stage breast cancer.
• Evaluating the risk of radiation-associated symptomatic pneumonitis is crucial for APBI safety.
• Previous studies suggest APBI may reduce lung dose compared to WBI.

Purpose of the Study:

• To assess the risk of symptomatic radiation pneumonitis following APBI in early-stage breast cancer.
• To determine the relationship between lung dose parameters (MLD, V20, V30) and pneumonitis incidence.
• To compare APBI lung doses with those typically seen in WBI.

Main Methods:

• A prospective trial (DRKS00004417) enrolled 170 early-stage breast cancer patients treated with APBI (38 Gy/10 fractions).
• Patient eligibility included specific tumor characteristics, age (≥50 years), and tumor bed clips.
• Median follow-up was 56 months, with detailed recording of lung dose metrics and pneumonitis events.

Main Results:

• Ipsilateral lung mean lung dose (MLD), V20, and V30 were 4.3 Gy, 3.0%, and 1.0%, respectively.
• Only one patient (0.6%) developed Grade 2 radiogenic pneumonitis, with higher lung doses (6.1 Gy, 7%, 3%) and increased radiosensitivity.
• APBI resulted in significantly lower lung doses compared to WBI.

Conclusions:

• APBI is associated with a very low risk of symptomatic radiation pneumonitis in selected early-stage breast cancer patients.
• An ipsilateral V20 < 3% appears to limit pneumonitis risk to exceptional cases with innate risk factors.
• APBI represents a safe and effective treatment option with favorable lung dosimetry compared to WBI.