ESTRO 2022 - Abstract Book

S1034

Abstract book

ESTRO 2022

PO-1223 Dosimetric Parameters Spontaneous Rib Fracture in Breast Cancer Patients Received Radiotherapy

D. Kim 1 , J.M. Park 2 , K.H. Shin 1

1 Seoul National University College of Medicine, Radiation Oncology, Seoul, Korea Republic of; 2 Seoul National University, Department of Radiation Oncology, Seoul, Korea Republic of Purpose or Objective Spontaneous rib fracture (SRF), a fracture that occurs without traumatic factors, is a relatively common late complication in treated breast cancer patients. This study evaluated the incidence and risk factors of ipsilateral SRF after radiotherapy (RT) in breast cancer patients based on bone scans. In addition, we identified dosimetric parameters that were significantly associated with ipsilateral SRF. Materials and Methods We retrospectively reviewed 2,205 patients with breast cancer who underwent RT between 2014 and 2016, and who were followed up with at least three times bone scans. Among patients, 44.3% received the conventional fractionation scheme, and 55.7% received the hypofractionated scheme. The endpoint was ipsilateral SRF detected by bone scans. In this study, we used an electron beam for tumor bed boost and patients who received a boost were excluded from the dosimetric analysis. In the no boost group (n=539), all ipsilateral ribs were contoured to build the dose-volume histograms. All dosimetric parameters of ribs were calculated into the equivalent dose in 2 Gy fractions (EQD2) to correct for fractionation dose. Results The median follow-up duration was 41.0 months. Ipsilateral SRF occurred in 17.0% of patients during the follow-up. In multivariate analysis, abnormal bone density and hypofractionated RT were significant clinical risk factors for ipsilateral SRF (P = 0.019 and P < 0.001, respectively). The maximum dose (Dmax) EQD2 was the most significant dosimetric parameter associated with ipsilateral SRF. The 5-year incidence of ipsilateral SRF for Dmax more than and less than 53 Gy were 47.3% and 12.1% (P < 0.001), and for rib volume receiving 40 Gy (V40) more than and less than 23% were 30.9% and 24.5% (P = 0.01), respectively. Other dosimetric parameters, including mean dose EQD2 of ribs, V20, V30, and ipsilateral rib volume were not significantly different. Conclusion Dmax EQD2 was the most relevant dosimetric parameter that predict the ipsilateral SRF in RT-treated breast cancer patients. In particular, the incidence of Ipsilateral SRF showed the most significant difference when Dmax EQD2 > 53 Gy. 1 San Giuseppe Moscati Hospital , Radiation Oncology Unit, Taranto, Italy; 2 San Giuseppe Moscati Hospital, Medical Oncology Unit, Taranto, Italy; 3 SS Annunziata Hospital , Breast Surgery, Taranto, Italy; 4 SS Annunziata Hospital, Breast Surgery, Taranto, Italy; 5 SS Annunziata Hospital, Breast Reconstructive Surgery, Taranto, Italy; 6 SS Annunziata Hospital, Anatomo- Pathology Unit, Taranto, Italy; 7 SS Annunziata Hospital, Breast Unit Senology , Taranto, Italy; 8 San Giuseppe Moscati Hospital , Medical Oncology Unit, Taranto, Italy; 9 San Giuseppe Moscati Hospital, Radiation Oncology Unit, Taranto, Italy Purpose or Objective The radiation oncologist’s role in the Breast Unit (BU) team got a decisive impact in the up-front making decision process in case of several breast cancer (BC) scenarios needing a tailored and organized combination with surgery and radiotherapy in case of mastectomy or breast conserving surgery (BCS). Materials and Methods From 2020-2021 250 breast cancer patients (pts) needing an up-front treatment discussion with radiation oncologist were observed in our BU team. Among them, 70 pts needed a change of the initial therapeutic program in light of these scenarios: 20 pts with ICD (a) , 15 pts with autoimmune diseases (LES and sclerodermia, b), 5 pts with arm impairment in the affected breast side (c), 30 pts with a response after neoadjuvant chemotherapy followed by mastectomy and chest wall implants with immediate or delayed reconstruction and adjuvant radiotherapy (d). Results Totally in 60% of cases the initial decision was changed (42 pts). Mastectomy without adjuvant RT was advised in 20 patients with early BC in case of ICD in the side of affected breast (a), in shoulders impairment (b) while in scenario c adjuvant RT was prescribed after a BCS in non active disease for 8 pts. In case of mastectomy after neoadjuvant chemotherapy, a delayed chest wall reconstruction with temporary implants was planned in 12 cases showing advanced breast cancers needing adjuvant RT on chest wall and nodal areas. Conclusion in the BU team discussion the radiation oncologist role is an emerging and relevant protagonist in the up-front tailoring making decision process. PO-1224 The radiation oncologist’s relevance in the Breast Unit team up-front discussion: our experience G. Lazzari 1 , A.R. D'Alessandro 2 , F. Cannalire 3 , M. Cramarossa 4 , R. D'Andria 5 , G. Marangi 6 , G. Melucci 7 , S. Pisconti 8 , G. Silvano 9