ESTRO 2022 - Abstract Book

S1027

Abstract book

ESTRO 2022

RTP by using PET-CT under the same conditions as treatment planning CT can improve the coverage of targets, affected axillary lymph nodes at diagnosis, in particular. Proposed “direct fusion” approach can contribute to avoid insufficient axillary management due to ostensible downstaging after NAC.

PO-1211 FSRT plus systemic therapy in patients with breast cancer bone metastases: feasibility and efficacy

S. Silipigni 1 , E. Ippolito 2 , P. Matteucci 2 , B. Floreno 2 , F. Giannetti 2 , I. Ridolfi 2 , C. Tacconi 2 , C. Talocco 2 , S. Carrafiello 2 , S. Ramella 2

1 Pol.Campus Biomedico , radiation oncology, Rome, Italy; 2 Pol.Campus Biomedico, radiation oncology, Rome, Italy

Purpose or Objective This study aims to assess the safety and efficacy of fractionated SRT (FSRT) associated to systemic therapy in patients with breast cancer bone metastases. Materials and Methods Patients with breast cancer bone metastases who were treated with FSRT within 21 days of receiving systemic therapy were identified. All lesions were treated with LINAC-based FSRT. Treatment was delivered using IMRT or VMAT in supine position using vacuum-locked or other customized devices. All patients received systemic therapy in relation to molecular pattern. Local control was evaluated at least after two months after treatment completion by means of radiological exams, while pain responses assessed at the end of treatment and every three months thereafter. Acute toxicity were reported and graded as per standardized Common Toxicity Criteria for Adverse Events 4.0 criteria. Results From January 2019 to March 2021,a total of 40 patients with breast cancer bone metastases were identified. The median age of patients at the time of RT was 54 years. All patients were treated with higher doses of radiotherapy delivered in three fractions according to the lesion’s site (Total dose 18 Gy, 21Gy or 27Gy). The most common treated site was axial skeleton (83%). 18 patients for a total of 29 lesions, were treated with FSRT and concurrent systemic therapy. Administrated sistemic therapy was as follow: 10 patients (55.6%) received CDK4/6 inhibitors (12 radiotherapy courses), 6 patients (33.3%) trastuzumab (12 radiotherapy courses), 2 patients (11,1%) Eribulin. The most common collateral effect observed was neutropenia, in particular in association with CDK4/6 inhibitors. All patients completed treatment without interruptions. During the follow-up the most used diagnostic exam was the PET/CT. With a median follow-up of 7 months (range: 1-24 months), we recorded: patients treated in association with CDK4/6 inhibitors had 2 complete response (CR), 4 partial response (PR), 5 stable disease (SD), 1 progression disease (PD); patients treated with trastuzumab 3 CR, 3 PR, 4 SD, 2 PD; all patients treated with Eribulin had SD. 13 treatments determined a pain relief, of which eight a complete pain response. Nobody developed pathologic fractures. Conclusion Highly hypofractionated radiation therapy is a feasible and tolerable treatment for bone metastases. Longer follow-up will be needed to accurately determine response and late effects. R.M. Niespolo 1 , S. Terrevazzi 2 , S. Trivellato 3 , C. Chissotti 2 , M.C. Innati 4 , P. Caricato 5 , V. Faccenda 6 , G. Montanari 5 , D. Panizza 5 , V. Pisoni 1 , S. Arcangeli 1 1 H.S. Gerardo, Radiation Oncology, Monza, Italy; 2 H.S. Gerardo, Radiation Oncology, Monza, Italy; 3 H.S. Gerardo, Physics Department, Monza, Italy; 4 H.S. Gerardo , Radiation Oncology, Monza, Italy; 5 H.S. Gerardo, Physics Department, Monza, Italy; 6 H.S. Gerardo, Physics Department, Monza, Italy Purpose or Objective Hypofractionated radiotherapy is not widespread, although recent studies have proven its non-inferiority after primary surgery for early-stage breast cancer (BC). This study analysed the preliminary data and factors influencing acute skin toxicity in BC patients, treated according to the radiotherapy FAST protocol. Materials and Methods Early-BC patients were treated with 28.5 Gy in 5 fractions once a week (FAST protocol) using the 3D-CRT field-in-field (FIF) technique at a single Institution. Clinical target volumes (CTVs), dosimetric parameters, and tumour characteristics were recorded and analysed. The parameters measured to assess the breast size are the cup size, the nipple-to-pectoral muscle distance (NPD), and the maximum medio-lateral thickness (MLT), along tangential fields. Adverse skin reactions were assessed according to CTCAE v. 5.0 at the end of treatment and after one month. Results Between December 2020 and October 2021, 34 early-BC patients (median age 66 years, 51–84) were enrolled, of whom 6 underwent forced deep-inspiration breath-hold. 57% of patients had fair skin (skin phototype I/II according to the Fitzpatrick scale). The median CTV volume was 393 cm 3 (60.3-855.7) with a median NPD of 4.7 cm (1.7-8) and a median MLT of 21.9 cm (14.3-32.3). The 5,8%, 34,2%, 40%, and 20% of patients wore an A, B, C, and D bra cup-size, respectively. CTVs registered a median V95% of 99.6% (96.6-100.0) and a median V105% of 0.1% (0.0-4.7). The median 105% isodose was 2.33 cm 3 (0.0- PO-1212 FAST protocol in breast radiotherapy: anthropometric parameters, dosimetric results and toxicity.