Accelerated partial breast irradiation with CyberKnife (CK-APBI) is a promising innovative approach for early breast cancer after conservative surgery, for addressing the need of a radiotherapy target only to the surgical cavity in selected patients, exceeding the limits of other PBI/APBI.

The large majority of local recurrences in breast cancer after breast conserving treatment are close to the original tumor site. This evidence suggested to restrict the radiotherapy target to the surgical cavity in selected patients. Consequently, shorter fractionation strategies focused only on tumor bed with a small cuff of surrounding subclinical disease, i.e. accelerated partial breast irradiation (APBI), were developed. Stereotactic radiotherapy was thought, consisting of a short course of intense treatment focused on the target tissue. There is very little experience with CiberKnife for early breast cancer until now.

This study is a prospective non-randomized study designed to assess the acute, sub-acute, late toxicity, cosmesis and globally the feasibility of CyberKnife (CK-APBI). From June 2013 to June 2018 we are going to enroll 80 patients considered eligible for the present study. All patients will be followed for at least 2 years. A first enrollment of 20-25 patients is scheduled as first assessment.

Breast magnetic resonance imaging (MRI) will be aided to mammography and ultrasound examination for confirming the best selection of patients.

For the assessment of acute toxicity, cosmetic results by three different observers (physician, patient, external observer), medium term and late toxicity, patients were evaluated and the results recorded immediately before and after radiotherapy, then after 1 month, three, six, nine, and twelve, and twenty-four months. The toxicity will be correlated to the main radiotherapy treatment dosimetry and delivery recorded.

Inclusion Criteria:

• Patients were ≥45 years of age with stage I-IIA histologically confirmed breast carcinoma, with tumor-free (at least 2 mm or more) inked histologic margins at surgical resection.

Exclusion Criteria:

• Invasive lobular or multicentric carcinoma;
• Extensive associated non-invasive ductal carcinoma (synchronous or previous); peritumoral vascular invasion (>3 vessels);
• BRCA mutation carriers,
• >4 involved axillary lymph nodes,
• Distant metastasis,
• Non-epithelial malignancies of the breast,
• Synchronous contralateral invasive carcinoma,
• Paget disease,
• History of previous malignancy (except non-melanoma skin cancers and in situ oral cavity and cervix carcinoma);
• Further exclusion criteria were pregnancy, collagen vascular disease, aesthetic additive prostheses, severe cardiac, pulmonary and liver diseases, infectious, psychiatric illness compromising the correct acquisition of informed consent.