Hypofractionation of partial breast irradiation using radiobiological models

Area of Science:

• Oncology
• Radiation Oncology
• Medical Physics

Background:

• Partial Breast Irradiation (PBI) is an alternative to whole breast irradiation.
• Hypofractionation aims to reduce treatment duration and patient burden.
• Radiation-induced fibrosis (RIF) is a potential side effect of radiotherapy.

Purpose of the Study:

• To reduce the number of fractions in PBI using radiobiological models.
• To assess the risk of moderate/severe radiation-induced fibrosis (RIF) with hypofractionated PBI.
• To report clinical outcomes of reduced-fraction PBI.

Main Methods:

• Patients received 40 Gy in 10 fractions (Group A) or 35 Gy in 7 fractions (Group B) using Intensity-Modulated Radiation Therapy (IMRT).
• Radiobiological models, including Biological Effective Dose (BED) and Normal Tissue Complication Probability (NTCP), were used to predict RIF.
• Prospective scoring of RIF during follow-up and fitting of the alpha/beta ratio for breast tissue were performed.

Main Results:

• Incidence of moderate/severe RIF was low: 5.9% in Group A and 5.3% in Group B.
• The NTCP model incorporating incomplete repair correction showed the best agreement with observed RIF incidence.
• The fitted alpha/beta ratio for breast tissue was 2.8 Gy, consistent with the assumed 3 Gy.

Conclusions:

• Hypofractionated PBI regimens were well-tolerated with low RIF rates.
• The NTCP model with incomplete repair correction accurately predicted RIF.
• The study supports the continuation of hypofractionation protocols, including 28 Gy in 4 fractions.