Evaluation of the surface radiation dose and dose gradient in early stage breast cancer using high-dose-rate brachytherapy MammoSite™ applicator

Purpose To monitor the radiation dose delivered and dose homogeneity to the skin and adjacent tissues around a MammoSite™ applicator. Methods and materials Radiation surface dose was measured on 67 consecutive patients with Stage T1–T2N0M0 breast cancer implanted with the MammoSite™ balloon. Thermoluminescent dosimeters and metal oxide semiconductor field effect transistors were used to measure surface dose directly over the balloon, contralateral breast, thyroid, axilla, and inframammary fold. The dose homogeneity was retrospectively studied from the treatment plans in 25 patients. Results The mean maximum skin dose was 267 cGy, with a range of 56–488 cGy per fraction, 4 cGy (±2 cGy) to the contralateral breast, 8 cGy (±4 cGy) to the thyroid, 47 cGy to the ipsilateral axilla (±33 cGy), and 52 cGy (±47 cGy) to the ipsilateral inframmammary fold. The mean dose gradients were 127%, 110%, 99%, 96%, and 89% for inflated volumes of 35, 40, 50, 60, and 70 mL, respectively. Conclusions All patients completed therapy with no or minimal skin reaction with radiation doses comparable to or better to external beam radiation. Considering the dose homogeneity, the larger inflated volume allows for better homogeneity of dose distribution, minimizes the volume of contiguous tissue that receives relatively high doses, and may reduce the risk of fat necrosis.