Dosimetric Comparison of Accelerated Partial Breast Irradiation Techniques: Multicatheter Interstitial Brachytherapy and Conformal External Beam Radiotherapy

Purpose: To compare dosimetric plans obtained in patients with breast cancer (BC) that underwent accelerated partial breast irradiation (APBI) by conformal external beam radiotherapy (EBRT) or interstitial high dose rate brachytherapy (HDRB).

Material and methods: From 2017 to 2022 APBI was performed in 210 patients with stage I–II BC (рТ₁N₀M₀–pT₂N₀M₀). APBI was delivered to the tumor bed: in 99 cases — by EBRT, in another 111 patients — by HDRB. Leſt breast was irradiated in 101 women: in 51 women using HDRB, in 50 patients — by EBRT. Following dosimetric parameters were used for comparison of the dosimetric plans: D_max – maximum dose in the organ at risk; D_med – mean dose in the organ at risk (heart, leſt main coronary artery and its descending branch, ipsilateral lung, breast, skin and subcutaneous tissues).

Results: When the tumor bed was irradiated by HDRB, in comparison with EBRT, D_max for the skin and subcutaneous tissue decreases from 98.4 % to 68.7 %, р < 0.002. The use of HDRB made it possible to reduce the radiation load on the ipsilateral lung: D_max decreased from 71.9 % to 42.7 % , р < 0.002; D_med was 5.5 % for HDRB and 2.9 % for EBRT, р > 0.05. On the contrary EBRT associated with higher dose to the breast D_med breast — 46 % in comparison with HDRB D_med breast — 16.5 % , р < 0.002. Dose to the heart was higher with HDBT D_max heart — 20.2 %, D_med heart was 4.9 % than with EBRT D_max heart — 14.4 %, D_med heart — 0.8 %. Dose to the left coronary artery with HDRB D_max — 6.5 % , D_med — 3.9 % was higher than with EBRT D_max — 3.3 % , D_med — 1.3 % . Dose to the descending branch of the left coronary artery was higher with HDRB D_max — 12.6 % , D_med — 9.3 % than with EBRT D_max — 8.9 % and D_med — 3.4 % . But this differences were non-significant (р > 0.05).

Conclusions. APBI by HDRB associated by significant reduction of the radiation dose to the ipsilateral breast lung, breast, skin and subcutaneous tissues.

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