The aim of this observational study is to evaluate a dose fractionation scheme for APBI using external radiotherapy with modulated intensity technique (IMRT), with the possible impact on the quality of life of patients as it decreases the treatment number of sessions and improves the efficiency and accessibility.

Breast cancer is the most common tumor among women; although its treatment used to be very aggressive, nowadays is based on the minimum effective treatment.

In non-metastatic patients, the therapeutical strategy is based on surgery, systemic therapy and radiotherapy. Usually in the early stages of the disease, the treatment begins with a conservative surgery followed by adjuvant therapy.

It´s been proved that the majority of relapses after conservatory surgery occur near the surgical bed which suggests that the main benefit of radiotherapy treatment lies in its primary effect on residual microscopic disease in the surgical bed. Regarding the radiotherapy used after conservative surgery, it´s accepted as standard treatment hypofractionated schemes, after they have demonstrated at least the same grade of effectiveness as the classic fractionation in terms of locoregional control, survival, aesthetic results or toxicity.

One of the options of hypofractionated schemes is APBI (Accelerated Partial Breast Irradiation), that by reducing the volume of the radiated breast and an accelerated dose fractionation scheme, can eliminate the residual microscopic disease in the surgical bed. The main advantage of APBI is that can shorten the overall time (total treatment time) by increasing the dose per fraction.

In patients who meet the following criteria:≥ 45 years or 40-44 if there isn´t any other risk factor, diagnosed with infiltrating ductal carcinoma (IDC) or ductal carcinoma in situ (DCIS) and that have undergone conservative surgery without ganglionar involvement (pN0) of any histological degree except from invasive lobular carcinoma and with a size ≤ 3 cm, with a free margin of at least 2 mm, as well as with positive and negative estrogen receptor tumors; APBI is currently considered standard treatment.

This radiotherapy modality can be administered using 4 different techniques: interstitial brachytherapy, spherical balloons, intraoperative radiotherapy with electrons or with dedicated kilovoltage (RIO) systems and External Radiotherapy (3D shaped RT or modulated intensity radiotherapy - IMRT-). Each of them have their advantages and disadvantages, without any of them being superior to the others in terms of survival or local control, however, IMRT achieves a more shaped and uniformed dose after conservative surgery.

The aim of this observational study is to evaluate a dose fractionation scheme for APBI (28 Gy in 5 fractions of 5.6 GY, 5 days/week) using external radiotherapy with modulated intensity technique (IMRT), with the possible impact on the quality of life of patients.

Inclusion Criteria:

• ≥ 45 years or 40-44 if there isn´t any other risk factor
• Diagnosed with infiltrating ductal carcinoma (IDC) or ductal carcinoma in situ (DCIS) and that have undergone conservative surgery without ganglionar involvement (pN0) of any histological degree except from invasive lobular carcinoma and with a size ≤ 3 cm.
• Disease free margins (R0: > 2mm).
• Positive and negative estrogen receptor tumors.

Exclusion Criteria:

• Multicentric and multifocal tumors, except from if it´s focal and the only risk factor.
• Patients must not have undergone a neoadjuvant QT therapy.
• Patients with BRCA positive mutation will be excluded.
• Those patients unable or unsuitable to understand and accept the informed consent.
• Metastasic´s affectation evidence.
• Extensive lymphovascular invasion, except from if the total resulting size of the focus and breast parenchyma addition is ≤ 3cm.
• Breast implants presence in the breast that´s going to be treated.
• Contraindicated radiotherapy treatment due to a diagnosis of cutaneous lupus, pregnancy or scleroderma.
• Inability to fully know the dosimetric data of the APBI plan.

Breast cancer patients that meet the inclusion criteria and none of the exclusion criteria.