Current breast cancer treatment is based on surgery, radiation, chemotherapy and hormonotherapy. Conservative surgery or mastectomy are followed by complementary externe radiotherapy.

This adjuvant external breast radiotherapy (EBRT) is heavy, spread over more than 6 weeks with :

• 25 sessions and delivery of a unit dose of 2 Gy to obtain a total dose of 50 Gy (5 sessions per week in general);
• 16 Gy overimpression (boost) dose located in the tumour bed, in 5 to 8 fractions, in situations at high risk of recurrence.

In addition, EBRT is responsible for many adverse effects, some of which can lead to lasting or permanent sequelae.

Many focused partial breast irradiation techniques have been developed in recent years with the objective of reducing the duration and morbidity of overall breast irradiation.

Among these techniques, intraoperative breast radiotherapy (IBRT) is recommended in cancers diagnosed at early stages for which tumorectomy is expected and which present a low risk of recurrence.

The main advantages of IBRTare :

• Improvement of the quality of life due to a single session of radiotherapy associated with surgical ;
• Increased precision to deliver the necessary dose in tumour tissue;
• Preservation of surrounding healthy tissue ;
• Reduction in the overall cost of treatment through shorter hospital stays and the absence of medical transport for conventional radiotherapy sessions.

RIOP SEIN is a project supported by Institut National du Cancer (INCa)

, which consists of a medico-economic evaluation of IBRT, with Intrabeam® system on surgical resection bed relative to conventional surgery + EBRT in postmenopausal patients operated by conservative surgery for Low risk breast cancer

Main objective is the economic comparison Intrabeam® system versus EBRT, in terms of real costs. Costs will be taken into account:

• of equipment,
• of staff,
• of transport.

Secondary objectives are :

• Compare local-regional survival without recurrence with conventional irradiation
• Analyze the rate of early and late complications
• Impact of intraoperative irradiation on the esthetic outcome and quality of life of patients

Schedule of the visits :

RIOP arm : Surgery with Intrabeam®. A first visit will be scheduled at 2 months from surgery then at 6 months then every 6 months for 5 years, then every year after 5 years.

RTE arm: surgery, EBRT over 33 sessions then visit at 6 months then every 6 months 6 for 5 years, then every year after 5 years.

In RIOP ARM, additional EBRT may be performed +/- chemotherapy if the treatment received is insufficient.

Quality of life will be assessed in each treatment arm at inclusion before randomization, 2 months after surgery, every 6 months for 5 years and every year after 5 years using quality of life questionnaires: Euroqol EQ 5D, European Organisation for Research and Treatment of Cancer (EORTC)-QlQ-C30 and BR23 module specific for breast cancer.

Inclusion Criteria:

• Histologically proven invasive ductal breast cancer,
• Menopausal women at least 55 years old,
• Clinical and ultrasound size ≤ to 20 mm, N0,
• Biopsy with all following criteria: SBR I or II, HER2 (0, +, ++ with FISH or SISH required), positive estrogen receptors, no embolus
• No personal history of breast cancer or BRCA gene mutation.
• Social insurance
• Signed consent

Exclusion Criteria:

• Bifocal or bilateral breast cancer,
• Presence of invasive ductal carcinoma with diffuse micro calcifications on mammography,
• Invasive lobular carcinoma,
• Presence of lymph node involvement,
• History of malignant disease if life expectancy without recurrence at 10 years <90%,
• Adult under guardianship,
• History of chest radiation therapy (Hodgkin's).