Sole brachytherapy of the tumor bed after breast conserving surgery: a new radiotherapeutic strategy for patients at low risk of local relapse.

The aim of the study was to test the hypothesis, if there were subgroups of early breast cancer patients in which sole brachytherapy (BT) of the tumor bed was a feasible and safe treatment option after breast conserving surgery (BCS). Forty four prospectively selected patients with Stage I-II breast cancer were entered into a protocol of postoperative tumor bed irradiation using interstitial high dose rate (HDR) implants. The HDR fractionation schedules were calculated according to the linear quadratic model. In 8 patients 7 x 4.33 Gy, in the other 36 patients 7 x 5.2 Gy were delivered to the tumor bed with 2 cm margin. The treatment planning was based on the 3 dimensional (3D) reconstruction of the clipped excision cavity, catheters and skin points. A conformal semi-3D dose planning was used. The side effects were assessed by mammograms, MRI- and clinical examinations. At a median follow up of 20 (7-36) months 1 (2.3%) local and 1 (2.3%) regional failure was observed. Distant metastasis did not occur. The cosmetic results were judged to be excellent in each case. G2 radiation side effects were observed in 2 (4.5%) cases. Postoperative sole BT of the tumor bed with careful patient selection and adequate quality assurance seems to be a feasible alternative to whole breast radiotherapy after BCS. Sole BT shortens the time of radiotherapy from 5-6 weeks to 5 days, and reduces the costs of treatment. The skin and volume sparing effect of interstitial irradiation may decrease the side effects of radiotherapy. A randomized study is in progress to define which subgroups of patients should be candidates for BT alone after BCS.