ESTRO 2021 Abstract Book

S558

ESTRO 2021

Poster discussions

Poster discussions: Poster discussion 1: Breast

PD-0728 Significance of liver metastasis volume in breast cancer treated with stereotactic body radiotherapy E. Oymak 1 , O.C. Güler 2 , C. Önal 2 1 Iskenderun Gelisim Hospital, Radiation Oncology, Hatay, Turkey; 2 Baskent University, Adana Dr. Turgut Noyan Research and Treatment Center, Radiation Oncology, Adana, Turkey Purpose or Objective The aim of this study is to analyze the impact of liver metastasis (LM) volume in breast cancer patients treated with stereotactic body radiotherapy (SBRT) on treatment outcomes. Materials and Methods A single-institution retrospective analysis was conducted. Oligometastatic or oligoprogressive (≤ 5 metastases) 40 breast cancer patients with a total of 58 liver metastases treated with SBRT between April 2013 and March 2021 were included. All patients were treated according to our institutional SBRT protocol. The prescribed dose was 54 Gy in 3 fractions delivered every other day. The planning goal for PTV was to deliver at least 95% of the prescribed dose, and the dose was prescribed to the 90% isodose line. Dose constraints were summarized in Table 1. Inclusion criteria were; KPS ³70, Child Pugh Status A-B, maximum LM diameter £6 cm, absence of coagulation abnormalities, life expectancy more than three months. Patients with any metastatic foci other than liver who remained under control with systemic chemotherapy and/or RT were included. LM were detected with FDG-PET-CT either at diagnosis or during distant progression. The prognostic factors for local control (LC), overall survival (OS) and progression-free survival (PFS) rates were assessed.

Results Patient characteristics are summarized in Table 2 (see above). Median follow-up was 28.1 months. Twenty six patients (65%) had isolated liver metastasis, and 24 (60%) had solitary LM. All patients had disease recurrence median 10.7 months (95% CI: 2.5–33.6 months) after completion of liver SBRT. The 2-year OS, PFS and LC rates were 71.4%, 27.5%, and 86.8%, respectively. In univariate analysis, GTV and PTV were significant prognostic factors for OS. The median OS was significantly better in patients with GTV ≤6 cc compared to patients with GTV >6 cc [50.9 months (95% CI, 39.1–62.6 months) vs. 18.8 months (95% CI, 7.3–30.3 months; p = 0.01) (Figure 1A). Median OS in patients with PTV ≤38 cc was 59.3 months (95% CI, 39.8–64.3 months; p =