Women found to have early stage breast cancer will have their cancer surgically removed followed by radiation treatment to the entire breast, five times per week for several weeks. The radiation treatment prevents the cancer from growing back but creates skin burns. Several studies have showed that it is nor necessary treating the whole breast.

The investigators team has pioneered a new therapy realizing the permanent implantation of tiny radioactive seeds into the surgical cavity in a single one hour procedure under light anesthesia. Patients live a normal life while receiving the radiation treatment. The results of a first clinical trial on 67 patients shows that the treatment is well tolerate and efficient. The purpose of the study is to offer the treatment in several places and to increase the cohort of patient to 420 to capture rare complications if any.

For early stage breast cancer, accelerated partial breast irradiation is an alternative treatment option to whole breast irradiation after breast conserving surgery. Our group has previously reported results of a Phase I/II study of permanent breast seed implant (PBSI) using palladium-103 seeds as an alternative to whole breast radiotherapy for well selected breast cancer patients. The procedure is realised in a single session under light sedation and local freezing. After a median FU of 54 months no patients has recurred on a cohort of 67 patients, and acute of delayed side effect compared favourably to external beam radiotherapy.

Yet this study was a single centre study and the sample size did not allow evaluating appropriately the risk of serious adverse events (SAE). The current study propose evaluating SAE on a multicentre and larger cohort of 420 patients.

Inclusion Criteria:

• A confirmed histological diagnosis of invasive breast carcinoma
• Treated by breast conserving surgery with axillary node dissection (with a minimum of 6 nodes sampled) or sentinel lymph node biopsy
• Surgical margins clear over or equal to 2 mm
• A maximum tumor size of 3 cm
• Age >= 50 years old
• ECOG performance status of 0 or 1
• Informed consent signed

Exclusion Criteria:

• Previous history of cancer other than curable skin SCC or Tis or T1 cervix
• Patient receiving anti-coagulant that cannot be stopped two weeks prior PBSI
• Autoimmune disorder
• Diabetes insulin-dependant
• Pregnancy
• Breast implants
• Psychiatric or addictive disorder that would preclude attending follow-up
• Post-operative breast infection
• Suspicious remaining microcalcification on post-surgery mammogram (unless biopsy proven benign)
• Lobular features on histology (pure or mixed) or sarcoma histology
• Node positive on axillary dissection or in the sentinel lymph node biopsy
• Extensive in situ carcinoma
• Multicentric disease (in more than one quadrant or separated by 2 cm or more)
• Paget's disease of the nipple
• Metastases
• Patients presenting a post-surgical fluid cavity ≥ 2.5 cm in diameter in any dimension as determined on the planning US
• Clear delineation of the target volume on CT is not possible
• Having a volume to be implanted over 120cc
• Having a target volume too close to skin such that the 85% isodose overlaps the skin surface)
• Having a target volume too close to the chest wall, such that there is a risk of perforating the chest wall