Biologic comparison of partial breast irradiation protocols.

Area of Science:

• Radiation oncology
• Medical physics
• Breast cancer treatment

Background:

• Partial breast irradiation (PBI) is an alternative to whole breast irradiation (WBI) after breast-conserving surgery.
• Assessing the biological effectiveness of different radiation fractionation schedules is crucial for optimizing cancer treatment outcomes.
• Clinical trials are exploring various PBI protocols, necessitating a comparison of their radiobiological impact.

Purpose of the Study:

• To analyze dose and fractionation schedules in ongoing partial breast irradiation (PBI) clinical trials.
• To compare the biologically effective dose (BED) of PBI protocols with standard whole breast irradiation (WBI) regimens.
• To evaluate PBI's radiobiological effectiveness for breast cancer treatment following segmental mastectomy.

Main Methods:

• Utilized the linear-quadratic model's BED equation to calculate BED values.
• Calculated BED for standard WBI regimens and various PBI protocols (external beam, high-dose-rate, and low-dose-rate brachytherapy).
• Compared BED values for tumor control and radiation-induced acute and late toxicities.

Main Results:

• Most PBI protocols yielded tumor control BEDs comparable to a 50-Gy standard treatment, but lower than 60-Gy or 66-Gy regimens.
• BED values for acute radiation responses (erythema, desquamation) were generally lower for PBI schedules.
• BED values for late radiation responses with PBI were similar to those of standard WBI treatments.

Conclusions:

• Biologically effective dose modeling suggests that PBI may deliver suboptimal doses for ensuring adequate in-field tumor control.
• The radiobiological dose delivered by PBI warrants careful consideration to balance treatment efficacy and toxicity.
• Further research and optimization of PBI fractionation schedules are needed to ensure comparable tumor control to standard WBI.