Breast dosimetry of ^99mTc-balloon in complementary radiotherapy

Dose reinforcement in primary tumor cavity can complement conventional radiotherapy in patients with early breast cancer. In this study, a dosimetric analysis was conducted by pertechnetate-^99mTc-filled balloon brachytherapy (TBB). Methods: Dosimetry based on radiochromic films and on a computational voxel thorax model was performed. Calibration protocol achieved a mathematical relationship between dose and optical density in films placed on the surface at a distance of 0–9 cm, 1 cm between them, in which dose values were provided by MCNP® code. Moreover, experimental spatial dose distribution was prepared. A female thorax voxel model was developed in the SISCODES®/MCNP® codes. Additionally, experimental and computational doses at 8–10 mm from balloon surface were compared. Results: Dose from ^99mTc-balloon, with 16 mm diameter, 32.22 GBq activity, and 24 h exposure time, achieved 8.08±0.42 (Ue) and 8.82±1.76 (Ue) Gy, at a distance of 10 mm from the balloon surface for the experimental data and computational modeling, respectively, thus showing nonsignificant difference. The spatial dose distribution in the chest wall, glandular tissue, breast skin, and lung was presented. The dosimetric findings supported the TBB modality presenting a suitable spatial dose distribution in the tumor bed and preserving the adjacent health tissues. Conclusion: TBB is a viable adjuvant brachytherapy modality for breast cancer in patients who have an appropriate indication. - Highlights: • Breast dosimetry of ^99mtc-balloon modality. • Complementary radiotherapy for breast cancer. • Boost dose application in breast cancer.