To report the implementation, dosimetric results of and early experiences with stereotactic accelerated partial breast irradiation (SAPBI) following breast conserving surgery (BCS) for postmenopausal low-risk St I-II invasive breast cancer (IBC) patients. Between November 2018 and August 2019, 27 patients were registered in our phase II prospective study. SAPBI was performed with Cyber-Knife (CK) M6 machine, in 4 daily fractions of 6.25 Gy to a total dose of 25 Gy. Respiratory movements were followed with implanted gold markers and Synchrony system. Corrections for patient displacement and respiratory movement during treatment were performed with the robotic arm. Early side effects, cosmetic results, and dosimetric parameters were assessed. The average volume of the surgical cavity, clinical target volume (CTV), and planning target volume (PTV_EVAL) were 8.1 cm³ (range: 1.75–27.3 cm³), 55.3 cm³ (range: 26.2–103.5 cm³), and 75.7 cm³ (range: 40–135.4 cm³), respectively. The mean value of the PTV_eval/whole breast volume ratio was 0.09 (range: 0.04–0.19). No grade 2 or worst acute side-effect was detected. Grade 1 (G1) erythema occurred in 6 (22.2%) patients, while G1 oedema was reported by 3 (11.1%) cases. G1 pain was observed in 1 (3.4%) patient. Cosmetic result were excellent in 17 (62.9%) and good in 10 (37.1%) patients. SAPBI with CK is a suitable and practicable technique for the delivery of APBI after BCS for low-risk, St. I-II. IBC. Our early findings are encouraging, CK-SAPBI performed with four daily fractions is convenient and perfectly tolerated by the patients.

为了报告绝经后低危St I-II浸润性乳腺癌（IBC）患者在保乳手术（BCS）后实施立体定向加速局部乳房照射（SAPBI）的实施情况，剂量学结果和早期经验。在2018年11月至2019年8月之间，我们的II期前瞻性研究中注册了27名患者。SAPBI用Cyber​​-Knife（CK）M6机器进行，每天4次，每次6.25 Gy，总剂量为25 Gy。呼吸运动后植入金标记和同步系统。使用机械臂对患者在治疗过程中的移位和呼吸运动进行校正。评估了早期副作用，美容效果和剂量参数。手术腔的平均体积，临床目标体积（CTV），³（范围：1.75–27.3 cm ³），55.3 cm ³（范围：26.2–103.5 cm ³）和75.7 cm ³（范围：40–135.4 cm ³）， 分别。PTV_eval /整个乳房体积比的平均值为0.09（范围：0.04-0.19）。未检测到2级或最严重的急性副作用。1（G1）级红斑发生在6名（22.2％）患者中，而G1水肿发生在3名（11.1％）患者中。1名（3.4％）患者观察到G1疼痛。整容结果出色的17例（62.9％），好的10例（37.1％）。具有CK的SAPBI是一种适用于BCS后低风险的I-II的APBI的合适可行技术。IBC。我们的早期发现令人鼓舞，每天进行四次CK-SAPBI手术很方便，患者可以完全耐受。