Background: Breast conserving surgery (BCS) plus external beam radiotherapy (EBRT) is considered the standard treatment for early breast cancer. We have investigated the possibility of irradiating the residual gland, using an innovative nuclear medicine approach named IART® (Intra-operative Avidination for Radionuclide Therapy).

Aim: The objective of this study was to determine the optimal dose of avidin with a fixed activity (3.7 GBq) of 90Y-biotin, in order to provide a boost of 20 Gy, followed by EBRT to the whole breast (WB) at the reduced dose of 40 Gy. Local and systemic toxicity, patient’s quality of life, including the cosmetic results after the combined treatment with IART® and EBRT, were assessed.

Methods: After tumour excision, the surgeon injected native avidin diluted in 30 ml of saline solution into and around the tumour bed (see video). Patients received one of three avidin dose levels: 50 mg (10 pts), 100 mg (15 pts) and 150 mg (10 pts). Between 12 to 24 h after surgery, 3.7 GBq 90Y-biotin spiked with 185 MBq 111In-biotin was administered intravenously (i.v.). Whole body scans and SPECT images were performed up to 30 h post-injection for dosimetric purposes. WB-EBRT was administered four weeks after the IART® boost. Local toxicity and quality of life were evaluated.

Results: Thirty-five patients were evaluated. No side effects were observed after avidin administration and 90Y-biotin infusion. An avidin dose level of 100 mg resulted the most appropriate in order to deliver the required radiation dose (19.5 4.0 Gy) to the surgical bed. At the end of IART®, no local toxicity occurred and the overall cosmetic result was good. The tolerance to the reduced EBRT was also good. The highest grade of transient local toxicity was G3, which occurred in 3/32 pts following the completion of WB-EBRT. The combination of IART® EBRT was well accepted by the patients, without any changes to their quality of life.