ESTRO 2023 - Abstract Book

S37

Saturday 13 May

ESTRO 2023

failure, genitourinary and gynaecological cancers were the most prevalent primary tumours, each being diagnosed in 22 (33.3%) cases. Furthermore, the predominant site of relapse (47%) was the pelvic area. Only 26% of locoregional relapses occurred contra laterally, with 74% occurring at the margin of the treatment field, or at the successive nodal station or at any nodes of the ipsilateral chain (Fig. 1). The sites of treatment which more frequently showed recurrences in neighbouring (marginal and successive) lymph node areas were the abdomen and the pelvis (41%, for both). The median follow-up of the overall series was 68 months (range 10-324 months).

Conclusion Relapses following SBRT/SRS nodal irradiation were somewhat more common in distant regions than in loco-regional sites in our study. The most common scenarios for locoregional relapse appear to be genitourinary or gynaecologic cancer and the pelvic site. Additionally, recurrences are not infrequent in the immediate surrounding lymph nodal sites. PD-0070 Repeat stereotactic body radiotherapy for oligometastatic disease S. Adilovic 1 , J. Willmann 2 , E. Vlaskou Badra 1 , S.M. Christ 1 , M. Ahmadsei 1 , S. Tanadini-Lang 1 , M. Mayinger 1 , M. Guckenberger 1 , N. Andratschke 1 1 University Hospital Zurich, Department of Radiation Oncology, Zurich, Switzerland; 2 Paul Scherrer Institute, Center for Proton Therapy, Villigen, Switzerland Purpose or Objective Patients with oligometastatic disease (OMD) treated with metastasis-directed local therapies (MDT) such as stereotactic body radiotherapy (SBRT) are at a high risk of developing new metastases, which might be amenable to repeat SBRT. Subgroup analyses of recent clinical trials indicate that repeat SBRT after disease progression might be crucial to derive a survival benefit. Here, we explore oncological outcomes of OMD patients treated with repeat SBRT and compare these to patients having received a single course of SBRT. Materials and Methods OMD patients with 1-5 metastases from solid organ malignancies, treated with SBRT to all lesions were included in this retrospective study. Patients were classified by the number of SBRT courses as MDT to all lesions (single vs repeat SBRT). Progression-free survival (PFS), widespread failure-free survival (WFFS) with >5 metastases, overall survival (OS), systemic therapy-free survival (STFS; only patients with oligorecurrent disease) and the cumulative incidence of first failure was analyzed. Patient and treatment characteristics at baseline and disease progression predicting the use of repeat SBRT were investigated using multiple logistic regression. Results Among 385 patients treated with SBRT for OMD, 129 (33.5%) were treated with repeat SBRT while 256 (66.5%) received a single course. The most common primary tumor was lung cancer (repeat: 34.1%; single: 35.2%), and the most common OMD state was metachronous oligorecurrence (repeat: 24.0%; single: 23.8%). Patients treated with repeat SBRT had significantly shorter PFS (p<0.0001; Fig. 1A). Distant metastases as first failure were more frequently observed in repeat SBRT patients (p<0.0001; Fig. 2). Yet, patients treated with repeat SBRT more often presented with only a single metastasis at distant failure (repeat: 40%, single: 22.2%, p=0.003). However, WFFS was comparable in both groups (p=0.47; Fig. 1B). Among patients with oligorecurrence, no difference in STFS was observed between repeat and single course SBRT patients (p=0.22; Fig. 1C). Median OS was longer in repeat SBRT patients (p=0.01). On multivariable analysis, a higher number of previous lines of systemic therapy (1 line: odds ratio [OR] 2.68, p=0.002; 2