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Recent studies have reported a higher than expected risk of ipsilateral breast tumor recurrence (IBTR) after breast conserving surgery (BCS) and a single dose of electron beam intra‐operative radiotherapy (IORT). This finding was the rationale to perform a retrospective single center cohort study evaluating the oncologic results of consecutive patients treated with BCS and IORT. Women were eligible if they had clinical low‐risk (N0, ≤2 cm unifocal, Bloom and Richardson grade 1–2), estrogen receptor‐positive and human‐epidermal‐growth‐factor‐receptor‐2‐negative breast cancer. Prior to BCS, pN0 status was determined by sentinel lymph node biopsy. Data on oncologic follow‐up were analyzed. Between 2012 and 2019, 306 consecutive patients were treated and analyzed, with a median age of 67 (50–86) years at diagnosis. Median follow‐up was 60 (8–120) months. Five‐year cumulative risk of IBTR was 13.4% (95% confidence interval [CI] 9.4–17.4). True in field recurrence was present in 3.9% of the patients. In 4.6% of the patients, the IBRT was classified as a local recurrence due to seeding of tumor cells in the cutis or subcutis most likely related to percutaneous biopsy. In 2.9% of the patients, the IBRT was a new outfield primary tumor. Three patients had a regional lymph node recurrence and two had distant metastases as first event. One breast cancer‐related death was observed. Estimated 5‐year overall survival was 89.8% (95% CI 86.0–93.6). In conclusion, although some of IBTR cases could have been prevented by adaptations in biopsy techniques and patient selection, BCS followed by IORT was associated with a substantial risk of IBTR. [ABSTRACT FROM AUTHOR]

Background: Deep learning (DL) models for auto-segmentation in radiotherapy have been extensively studied in retrospective and pilot settings. However, these studies might not reflect the clinical setting. This study compares the use of a clinically implemented in-house trained DL segmentation model for breast cancer to a previously performed pilot study to assess possible differences in performance or acceptability., Material and Methods: Sixty patients with whole breast radiotherapy, with or without an indication for locoregional radiotherapy were included. Structures were qualitatively scored by radiotherapy technologists and radiation oncologists. Quantitative evaluation was performed using dice-similarity coefficient (DSC), 95th percentile of Hausdorff Distance (95%HD) and surface DSC (sDSC), and time needed for generating, checking, and correcting structures was measured., Results: Ninety-three percent of all contours in clinic were scored as clinically acceptable or usable as a starting point, comparable to 92% achieved in the pilot study. Compared to the pilot study, no significant changes in time reduction were achieved for organs at risks (OARs). For target volumes, significantly more time was needed compared to the pilot study for patients including lymph node levels 1-4, although time reduction was still 33% compared to manual segmentation. Almost all contours have better DSC and 95%HD than inter-observer variations. Only CTVn4 scored worse for both metrics, and the thyroid had a higher 95%HD value., Interpretation: The use of the DL model in clinical practice is comparable to the pilot study, showing high acceptability rates and time reduction.