High Dose Rate Brachytherapy in Treatment of Breast Cancer Patients

Purpose: To perform dosimetric comparison of interstitial high dose rate brachytherapy (HDRB) and electron boost to the tumor bed after breast conserving therapy.

Material and methods: In 62 patients with stage IA–IIIA breast cancer (pT₁N₀M₀–pT₂N₂M₀) HDRB was used to deliver a boost to the tumor bed. In all the cases preimplantation CT with markers on the scar and nipple was used for planning of the procedure. Tumor bed was determined by markers that were implanted during surgery with consideration of the tumor localization determined on pre-surgery staging CT. Insertion of the needles was performed under CT navigation. Postimplant CT was used for final planning with inverse and graphical optimization.

All brachytherapy plans were compared according to the following dosimetric parameters: V₉₀ (%) – percentage of СTV receiving 90 % of prescribed dose;); D_mean  – mean dose at organ at risk; D_max  – maximum dose in the organ at risk (heart, left main coronary artery and its descending branch, ipsilateral lung, breast, skin and subcutaneous tissue, liver). Other parameters (V₁₀₀, DNR, CI, COIN) were calculated but not reported in this abstract.

Results: The use of brachytherapy with a high dose rate ¹⁹²Ir source makes it possible to more accurately irradiate the bed: the mean value of D₉₀ using brachytherapy was 93.1 % (69.1 % –118 %), while D₉₀ was lower than 80 % in only 8 patients. The use of high-dose brachytherapy allows reducing the radiation load on the organs at risk: the myocardium and coronary vessels, especially during left-side localization of the process. D_med for these structures – 2.2 %; 3.4 % for the main trunk of the left coronary artery; 6.9 % for anterior descending branch of the left coronary artery; on the ipsilateral lung D_max  – 26.8 % (4.7 % – 76.7 %), D_med  – 2.3 % (0.8 % – 10.8 %). Also during CT scan, in 71 % of cases, there was a discrepancy between the topography of the cutaneous scar and the radiopaque interstitial marks established by the surgeons during the operation.

Conclusions: The use of brachytherapy improves the accuracy of irradiation of the tumour bed and significantly reduce radiation dose to the organs at risk: main trunk of the left coronary artery, descending branch of the left coronary artery, ipsilateral lung, skin and subcutaneous tissue.

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