S13
Track-Topic
ESTRO 2026
Table. Dose-volume parameters in high-dose-rate postoperative and perioperative interstitial brachytherapy (BT) of breast cancer. NTB: non- target breast. *Mann-Whitney U Test **median ***in left side breast tumours Conclusion: The perioperative concept with target definition only after implantation leads to poorer quality dose plans, as the inserted needles generally do not conformally cover the target volume. In the second breast- conserving BT, several weeks after surgery, the position of the tumour bed often would no longer allow implantation (too deep or too medial/lateral). However, even with this suboptimal irradiation, the local recurrence and overall survival results are just as good as if the patient had undergone mastectomy. However, perioperative BT is not recommended in primary breast tumours. Instead, CT-guided postoperative implantation is recommended. Keywords: partial breast, perioperative brachytherapy Intraoperative radiotherapy (IORT) for early breast cancer: 10-year outcomes from a single-institution cohort Yu Hsiao 1 , Yueh-Chun Lee 1,2 , Ying-Hsiang Chou 1,3 , Su- Chien Liao 4 , Shu-Jen Kuo 4 1 Radiation Oncology Department, Chung Shan Medical University Hospital, Taichung City, Taiwan. 2 School of Medicine, Chung Shan Medical University, Taichung City, Taiwan. 3 Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung City, Taiwan. 4 Cancer Center, Chung Shan Medical University Hospital, Taichung City, Taiwan Purpose/Objective: Real-world, long-term outcomes for guideline- concordant intraoperative radiotherapy (IORT) remain limited. We aimed to analyze the 10-year oncologic Digital Poster 3609 outcomes (IBTR, LRRFS, DMFS, EFS, OS) from our single-institution retrospective cohort , selected according to ASTRO partial-breast irradiation (PBI)
determined after the implantation, based on the histological results. So, the quality of the implantation is only revealed afterwards, which can lead to a suboptimal dose plan. Therefore, we compared the dose-volume parameters and quality indices of the postoperative and perioperative plans using the Mann-Whitney U test. Results: The planning target volume and the ratio of the target volume and the ipsilateral breast volume were significantly larger in perioperative than in postoperative breast BT (53.0 vs. 38.9 cm3, p=0.0147 and 0.12 vs. 0.07, p<0.001). The number of implanted needles was fewer (10 vs. 14, p<0.001), the dose coverage of the target volume was smaller (V100: 87.6 vs. 91.5%, p=0.0058), and the dose homogeneity was worse (DNR: 0.43 vs. 0.33, p<0.001). The volumes receiving high doses were larger (V150: 43.4 vs. 31.9%, p<0.001). Therefore, the dose plans for perioperative implants were understandably less conformal, but without statistical significance (COIN: 0.59 vs. 0.64, p=0.1167). In the case of non-target breast (V50: 12.5 vs. 8.1, p<0.001), skin (D1: 62.0 vs. 40.6, p<0.001), lungs (D0.1: 49.3 vs. 36.9, p=0.0049), ribs (D0.1: 78.6 vs. 49.6, p<0.001), and left-sided tumours, the dose to the heart (D0.1: 16.1 vs. 10.5, p=0.0089) was also higher in the perioperative case. The detailed results are in the Table.
consensus guidelines. Material/Methods:
We conducted a single-institution retrospective cohort at the Department of Radiation Oncology, Chung Shan Medical University Hospital (Taichung, Taiwan). Consecutive early breast cancer patients receiving IORT between 21 May 2014 and 1 February 2024 were included. Eligibility followed ASTRO partial-breast irradiation (PBI) consensus, prioritizing “Suitable” features (e.g., age ≥ 50 years, unifocal invasive tumour ≤ 2–3 cm or low-risk DCIS, negative margins, pathologic node-negative, ER-positive, no lymphovascular invasion). A protocol-defined subset of “Cautionary”
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