S10
Track-Topic
ESTRO 2026
Material/Methods: The study was initiated in 2019 (NCT04293796). All 40 patients included in the study before the start of NAST underwent SPECT-CT with 99mTc-MIBI for visualisation of the primary tumour. In women that reach complete instrumental response VAB was performed to prove pCR. Finally pCR was diagnosed in 28 (70%) of enrolled 40 patients. Clips were placed in the primary tumor volume (PrTV) before NAST initiation and during the VAB. Patients with pCR (28 women) underwent whole- breast irradiation with a boost to the PrTV. High-dose rate brachytherapy (HDRB) was the primary technique for boost delivery. Before CT guided needle insertion all patients underwent pre-insertion CT with subsequent fusion with pre-NAST SPECT-CT. In the cases of concordant topography of the clips and primary tumor HDRB was initiated, if it was differences in the clips and tumor position we used alternative approaches. Results: A complete overlap between the PrTV on the pre- treatment CT and the clip location on the simulation CT was observed in 16 (57.1%) patients, while a partial mismatch was noted in 5 (17.9%). HDRB performed in 20 of these 21 patients and electron boost was delivered in one case because of the close position of PrTV to the skin. A marked discrepancy between the PrTV and clip topography on the fused images was found in 7 (25%) cases. Among these, clips were not detected on simulation CT in 3 (10.7%) patients. In 5 of these 7 patients, fused images revealed anatomical landmarks (scar, fibrosis) that can be used for gross tumor volume identification and navigation of the needles. Finally, HDRBT was successfully used for boost delivery in 25 (89.2%) of these 28 patients, while a photon boost was applied in another 2 (7.2%) cases, and an electron boost in one (3.6%) women. Local recurrence was diagnosed in 2 (7.2%) of the 28 patients with pCR (mean follow-up 30 months). In one case, the recurrence was located in a different quadrant than the PrTV, suggesting initial multicentric tumor growth. Conclusion: The combination of clips placed during vacuum assisted biopsy with the fusion of pre-NAST and simulation CT images is crucial for accurate boost delivery. Keywords: surgery deescalation, boost, breast cancer
64,66cc29,32cc114,14cc21,04Diference 88,35cc 85,14cc21,48cc210,56cc48,93Table 1. Descriptive statistical analysis for V95% and V10mm volumes Statistically significant correlation was identified between V95% and V10mm using Spearman’s rank correlation coefficient and Kendall’s tau test (p < 0.001). The Wilcoxon signed-rank test for paired samples demonstrated a statistically significant difference between the medians of the two volumes (p < 0.001). Conclusion: Comparative analysis revealed that the boost irradiated volume with EBRT was more than twice that ofthe boost irradiated volume with IORT, with the difference reaching statistical significance. These findings suggest a consistent volumetric relationship between both techniques, and a substantial reduction of the irradiated volume with IORT Keywords: Intraoperative Radiotherapy, boost volume. References: 1 Customized computed tomography-based boost volumes in breast-conserving therapy use of the three- dimensional histologic information for clinical target volume margins.Bianca Hambeukers, M.A.et al. J. Radiation Oncology Biol. Phys., Vol. 75, No. 3, pp. 757– 763, 20092.Volume matters: Breast induration is associated with irradiated breast volume in the Danish Breast Cancer Group phase III randomized Partial Breast Irradiation trial. Mette S. Thomsen et al Radiotherapy and Oncology 177 (2022) 231–2353. Long-term results of targeted Intraoperative Radiotherapy (target) boost during breast-conserving surgery. Jayant s. Vaidya et al. Int. J.. Radiation Oncology Biology.Phys., Vol. 81,Nº. 4 pp. 1091-1097, 2011 Digital Poster Highlight 1998 Strategy of high dose rate brachytherapy boost delivery in “surgery de-escalation” study. Sergey N Novikov 1 , Zhanna Bryantceva 1 , Irina Akulova 1 , Petr Krivorotko 2 , Nikolay Amirov 2 , Olga Ponomareva 1 , Sergey Kanaev 1 1 Radiotherapy, N.N. Petrov Cancer Institute, St Petersburg, Russian Federation. 2 breast surgery, N.N. Petrov Cancer Institute, St Petersburg, Russian Federation Purpose/Objective: To evaluate different approaches to target volume definition and technique of boost delivery in patients with a complete pathologic response (cPR) to neoadjuvant systemic therapy (NAST) who underwent radiotherapy with “surgery de-escalation” to vacuum- assisted breast (VAB) and sentinel lymph node biopsy.
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