Equivalent uniform dose for accelerated partial breast irradiation using the MammoSite applicator.

Area of Science:

• Medical Physics
• Radiation Oncology
• Brachytherapy

Background:

• The MammoSite applicator is used for accelerated partial breast irradiation (APBI).
• Understanding the radiobiology of MammoSite is crucial for optimizing treatment and minimizing toxicity.
• The relationship between equivalent uniform dose (EUD) and radiotherapy-associated toxicity needs further investigation.

Purpose of the Study:

• To quantify the radiobiology of the MammoSite applicator.
• To examine the association between EUD and radiotherapy-induced toxicity.
• To assess the utility of EUD in characterizing dose distributions in brachytherapy.

Main Methods:

• Utilized a linear quadratic (LQ) model adapted for brachytherapy dose gradients.
• Calculated biological effective dose (BED), EQD2, and EUD for a common MammoSite fractionation scheme (34 Gy in 10 fractions).
• Assessed acute and late toxicity in patients treated with MammoSite and investigated statistical associations with EUD.

Main Results:

• Acute and late toxicity EUDs ranged from 34.8-39.4 Gy and 33.4-37.6 Gy, respectively.
• EUD decreased with increasing balloon diameter and/or number of dwell positions.
• A positive association was observed between EUD and hyperpigmentation and telangiectasia.

Conclusions:

• For APBI with MammoSite, EUD exceeds the marginal prescription dose.
• The calculated EUD was associated with acute and late skin toxicity.
• EUD shows potential as a parameter for characterizing non-uniform dose distributions in brachytherapy.