hypofractionated WBI Total dose 40.05 Gy (15 x 2.67 Gy)

Local tumor control in the index quadrant of the ipsilateral breast as a secondary endpoint is defined as no tumor relapse in the breast tissue quadrant of the initial tumor/ at the site of surgical intervention. Local tumor control in the index quadrant of the ipsilateral breast is used as an additional secondary endpoint to distinguish between true local recurrences in the index quadrant from second (or new) ipsilateral carcinomas in other quadrants. In the intraoperative study arm (arm B) only the former tumor bed is irradiated, while in study arm A the whole breast tissue is irradiated.

Local tumor control in the index quadrant of the breast is taken as number of days from randomization until local tumor progression, death without prior local progression, or end of follow-up. For patients alive and not diagnosed with local progression at the end of the study, the local control time will be censored at the time of the last study visit.

Local tumor control in the ipsilateral breast as a secondary endpoint is defined as no tumor relapse in the whole ipsilateral breast tissue. Local tumor control in the ipsilateral breast is taken as number of days from randomization until local tumor progression, death without prior local progression, or end of follow-up. For patients alive and not diagnosed with local progression at the end of the study, the local control time will be censored at the time of the last study visit.

Local tumor control in the index quadrant of the breast is taken as number of days from randomization until local tumor progression, death without prior local progression, or end of follow-up. For patients alive and not diagnosed with local progression at the end of the study, the local control time will be censored at the time of the last study visit.

QoL will be analyzed with the help of the EORTC QLQ-C30. Scores are interpreted according to the guidelines of the EORTC Scoring Manual.

The BREAST-Q questionnaire is specifically designed for patients undergoing BCS measuring quality-of-life (QOL) and satisfaction. Patients are asked to rate each item question on a four-point scale. The BREAST-Q is separated into a pre- and post-surgery version.

The Breast Cancer Treatment outcome scale (BCTOS-12) contains 12 items, which are assigned to two internally consistent subscales: 1) Functional Status, 2) Aesthetic Status. Patients are instructed to rate each item of the BCTOS-12 on a four-point scale evaluating the differences between the treated and the untreated breast (1 = no difference, 4 = large difference). The score for each subscale is the mean of the ratings over all items belonging to that subscale. A higher score reflects a poorer status (i.e. a larger difference between the treated and the untreated breast).

Distant tumor control is defined as no occurrence of distant metastases (lymph node metastases in the axilla, supraclavicular fossa and internal mammary chain are not classified as distant metastases, see above). Distant tumor control is defined as number of days from randomization until occurrence of distant metastases, death without prior distant progression, or end of follow-up. For patients alive and not diagnosed with distant progression at the end of the study, the distant tumor control time will be censored at the time of the last study visit.

Overall survival time, defined as number of days from randomization until death or end of follow-up. For patients alive at the end of the study, the overall survival time will be censored at the time of the last visit or follow-up contact.

Disease-free survival, defined as number of days from randomization until the first occurrence of local recurrence, regional lymph node metastases, distant metastases, tumor-related death, death without prior progression, or end of follow-up. For patients alive and not diagnosed with progression at the end of the study, the disease-free survival time will be censored at the time the patient was last known to be free of progression of tumor disease.

Frequency of secondary malignancies after 2 and 5 years will be assessed

Detailed acute potentially therapy-related toxicity will be assessed during each follow-up visit and documentation of side-effects with Common Terminology Criteria for Adverse Events and with the Radiation Therapy Oncology Group (RTOG)/ European Organization for Research and Treatment of Cancer (EORTC) Late Radiation Morbidity Scoring System Schema. Documentation of toxicity will mainly focus on breast shrinkage/distortion, breast induration/ fibrosis, change of skin appearance, telangiectasia, breast oedema, numbness, fat necrosis and local pain.

Detailed chronic potentially therapy-related toxicity will be assessed during each follow-up visit and documentation of side-effects with Common Terminology Criteria for Adverse Events and with the Radiation Therapy Oncology Group (RTOG)/ European Organization for Research and Treatment of Cancer (EORTC) Late Radiation Morbidity Scoring System Schema. Documentation of toxicity will mainly focus on breast shrinkage/distortion, breast induration/ fibrosis, change of skin appearance, telangiectasia, breast oedema, numbness, fat necrosis and local pain.

Photographic assessments before and after BCS will be taken at baseline and during follow up visits. Evaluation of breast cosmesis will be performed according to the proposed method by Vrieling et al (Schmidt ME, Chang-Claude J, Vrieling A, et al. Fatigue and quality of life in breast cancer survivors: temporal courses and long-term pattern. Journal of cancer survivorship : research and practice 2012;6:11-19.)

Regional tumor control is regarded as no occurrence of regional lymph node metastases (axilla, supraclavicular fossa, internal mammary chain). Regional tumor control is defined as number of days from randomization until occurrence of regional lymph node metastases, death without prior regional tumor progression, or end of follow-up. For patients alive and not diagnosed with regional progression at the end of the study, the regional tumor control time will be censored at the time of the last study visit.