Radiation recall reaction with docetaxel administration after accelerated partial breast irradiation with electronic brachytherapy

Purpose: Accelerated partial breast irradiation (APBI) offers several advantages over whole breast irradiation. Electronic brachytherapy may further reduce barriers to breast conserving therapy by making APBI more available. However, its toxicity profile is not well characterized. Methods and Materials: A 60-year-old woman was treated with APBI using Axxent (Xoft, Sunnyvale, CA) electronic brachytherapy. One month after APBI, a cycle of docetaxel and cyclophosphamide was given. Within 3 weeks, the patient developed an ulcerative radiation recall reaction in the skin overlying the lumpectomy cavity. To investigate this toxicity, the skin dose from electronic brachytherapy was compared with the dose that would have been delivered by an iridium-192 (¹⁹²Ir) source. Additionally, a dose equivalent was estimated by adjusting for the increased relative biologic effectiveness (RBE) of low energy photons generated by the electronic source. Results: Using electronic brachytherapy, the skin dose was 537 cGy per fraction compared with 470 cGy for an ¹⁹²Ir source. Given an RBE for a 40 kV source of 1.28 compared with ¹⁹²Ir, the equivalent dose at the skin for an electronic source was 687 cGy-equivalents, a 46% increase. Conclusions: We present a case of an ulcerative radiation recall reaction in a patient receiving APBI with electronic brachytherapy followed by chemotherapy. Our analysis shows that the use of electronic brachytherapy resulted in the deposition of significantly higher equivalent dose at the skin compared with ¹⁹²Ir. These findings suggest that standard guidelines (e.g., surface-to-skin distance) that apply to ¹⁹²Ir-based balloon brachytherapy may not be applicable to electronic brachytherapy.