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 (рТ 1 N 0 M 0 –pT 2 N 0 M 0 ). 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.