ESTRO 2023 - Abstract Book

S172

Saturday 13 May

ESTRO 2023

Data obtained from medical records of breast cancer (BC) patients, who underwent NSM and SSM at a single institution, between 2004 and 2018, were retrospectively analyzed to identify patients’ patterns of first breast cancer recurrence as well as their demographics, disease characteristics, systemic and surgical treatments, and the use of postmastectomy radiotherapy (PMRT) Results 248 BC patients were identified, with a median age at diagnosis of 47-years(21-78), invasive disease in 215(86.7%) and DCIS in 33(13.3%). 144(58%) underwent NSM, and 104(42%) SSM. Overall, 33% received PMRT, 9(15%) patients with N0 disease, see Table 1 for detail. BRCA 1/2 mutations were identified in 41(17%) patients, although mutation status was not established in 54% of patients. 32% received preoperative chemotherapy while 35% did postoperatively. Of all first recurrences, 21%(4) were local, at scar level and 21%(4) were regional, at lymph node level; 58%(13) were reported as distant. No simultaneous loco-regional recurrence was reported, as well as no simultaneous loco-regional + distant recurrence. In terms of surgical technique, no significant difference was found regarding locoregional and distant recurrence when comparing NSM and SSM. In contrast, while comparing PMRT vs non-PMRT, more recurrence events, any kind (12 vs 9, p=0.04) and more distant recurrences (8 vs 5 p=0.009) were reported in the PMRT group. 98% of patients were alive at the time of last follow-up

Conclusion A low rate of recurrence was observed in this large series of patients, operated for DCIS or invasive breast cancer with NSM or SSM, with no apparent difference in patterns of recurrence according to surgical technique. More local and distant recurrences were observed after PMRT, due to more advanced stage of disease allocated to this group. Further follow-up will allow to better define the long-term oncologic outcomes of these two techniques PD-0237 Intrafractional dose coverage of the internal mammary nodes in high-risk breast cancer patients A.W.M. Nielsen 1 , H. Spejlborg 2 , P.R. Poulsen 3,4 , B.V. Offersen 1,4,3 1 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark; 2 Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark; 3 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark; 4 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark Purpose or Objective Internal mammary node (IMN) irradiation in high-risk breast cancer patients improves overall survival. The Danish Breast Cancer Group (DBCG) guidelines for adjuvant breast cancer radiotherapy recommend ≥ 98% of the IMN CTV receives 90% of the prescribed dose (V90_CTVn_IMN). No PTV dose coverage is required. This leaves little room for intrafractional movements. This study examines the delivered IMN dose coverage at treatment using continuous portal images (CINE MV) of tangential breast fields. Materials and Methods A prospective single-center quality assurance study was conducted in a consecutive cohort of left-sided node-positive breast cancer patients treated during 2021 using a wide tangential field technique under deep-inspiration breath-hold (DIBH).