MammoSite multilumen catheter: Dosimetry considerations

Purpose: To explore the dosimetric advantages of the new MammoSite multilumen (ML) balloon for breast brachytherapy treatment compared to conventional single lumen (SL) device plan.
Materials and Methods: Patients deemed appropriate for accelerated partial breast irradiation (APBI) were implanted with the MammoSite ML balloon. Two plans were generated in each patient for the same target coverage (PTV_EVAL) and dose to normal structures were plotted. The first plan used only the central single lumen with single-dwell position (SL), and the second plan (ML) was generated using the other lumens of the device. Dose distributions of the SL and ML plans were compared.
Results: For the same PTV_EVAL, the ML balloon improved dose coverage at the tip and base of the applicator compared to SL plan. The skin and rib doses were reduced using the ML plan versus SL plan for the same PTV_EVAL in-patient 2, where the skin-balloon distance was 7 mm and the rib-balloon distance was <1 cm. For patient 1, the skin and rib distances were greater than 1 cm and the ML plan did not further minimize the dose to normal structures.
Conclusion: In our initial experience, dosimetric goals can be better achieved using the ML MammoSite balloon when normal structures (skin and ribs) are close to PTV_EVAL with a distance of <7 mm and rib distance of <1 cm. The multiple lumen of ML balloon can optimize dose and reduce excessive dose to rib and skin and therefore minimize the long-term toxicities of rib discomfort, skin fibrosis and fat necrosis.

Keywords
Accelerated partial breast irradiation, balloon catheter, brachytherapy, breast cancer, multilumen MammoSite