To evaluate safety of 5 fraction accelerated partial brest irradiation in more convenient 5 fraction schedule.

The purpose of this study is to evaluate the rate of early and intermediate toxicity related to accelerated partial breast irradiation (APBI) delivered in a more convenient 5 fraction schedule using non-invasive image-guided breast brachytherapy (NIBB) (AccuBoost System) in women with resected, early stage breast cancer.

Non-invasive image-guided breast brachytherapy (NIBB), using advanced image-guided radiation technology, has the potential to eliminate the disadvantages of the conventional APBI techniques. NIBB facilitates non-invasive partial breast irradiation without the use of catheters or implants. Yet by using breast immobilization and precise image-guidance, it reduces non-target breast tissue within the irradiated field compared with other non-invasive APBI techniques such as 3D-CRT. This has made NIBB an attractive approach to deliver APBI.

We hypothesize that NIBB delivered in 5 treatments will be a more convenient, safe and effective modality to deliver partial breast irradiation.

Anticipated advantages of NIBB protocol treatment include:

• Convenient treatment schedule
• Short course can allow for increased patient access to treatment
• Non-invasive approach
• Increased accuracy with precise targeting of lumpectomy cavity using advanced imaging
• Reduced irradiation of non-target breast tissue
• Reduced skin toxicity
• No heart or lung radiation exposure
• Reduced late skin or breast toxicity
• High rate of good or excellent cosmetic outcome
• High rate of ipsilateral breast tumor control comparable to other APBI techniques

Inclusion Criteria:

1. A confirmed histological diagnosis of invasive breast carcinoma or DCIS;

2. Age greater or equal to 50 years old;

3. Life expectancy > 6 months;

4. Treated by breast conserving surgery

5. Pathologic lymph node negative, which includes (pN0 i-, i+);

   Patients, who are at very low risk for sentinel node involvement and sentinel node biopsy is not performed, are eligible if the treating investigator documents clinically lymph node negative (cN0). These patients include:

   • DCIS
   • Microinvasion only
   • Pure tubular or mucinous histology
   • Patients ≥ 70yo with T1a-T1c; estrogen receptor +

6. Pathologic tumor size

   1. less than or equal to 2 cm for invasive disease;
   2. less than or equal to 3 cm for DCIS;

7. Estrogen receptor positive if invasive disease (DCIS can be ER negative)

8. Negative surgical margins greater than or equal to 2 mm. A margin of <2mm is acceptable if at natural boundary, i.e. skin or pectoralis fascia.

9. No lymphovascular invasion;

10. ECOG performance status of 0-2 (Appendix 1);

11. Informed consent signed.

Exclusion Criteria:

1. Known BRCA 1/2 Mutation; (BRCA 1 and 2 testing is not required)
2. Active lupus or scleraderma;
3. Pregnancy;
4. Psychiatric or addictive disorder that would preclude attending follow-up;
5. Neoadjuvant chemotherapy (adjuvant chemotherapy is permitted);
6. Suspicious remaining microcalcification on post-surgery mammogram (unless biopsy proven benign);
7. pN+ on axillary dissection or in the sentinel lymph node biopsy (N0i+ are considered node negative and are not excluded);
8. Multicentric disease;
9. Paget's disease of the nipple;
10. Breast Implants
11. Distant metastases;
12. Lumpectomy cavity not well visualized on AccuBoost imaging;
13. Lumpectomy cavity with 1cm margin (CTV/PTV) not adequately encompassed by any available applicator.
14. Breast separation with compression > 8cm at time of simulation.

Data was collected from signing of ICF until 5 years post treatment.