ESTRO 2024 - Abstract Book

S1933

Clinical - Mixed sites, palliation

ESTRO 2024

Ivica Ratosa 1,2 , Alenka Culk 2 , Anja Rankovec 2 , Janja Sedlar 2 , Miha Orazem 1,2 , Eva Ciric 1 , Gaber Plavc 1,2 , Barbara Segedin 1,2 , Ajra Secerov Ermenc 1,2 , Jasna But Hadzic 1,2 1 Institute of Oncology, Division of Radiotherapy, Ljubljana, Slovenia. 2 University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia

Purpose/Objective:

The aim of our study was to analyse local control and toxicity after SBRT of spine or non-spine bone metastases in patients with oligometastic cancer, treated at the Institute of Oncology Ljubljana (OIL). In addition, we aimed to analyse oligometastatic bone disease classified according to the ESTRO-EORTC nomenclature.

Material/Methods:

The study cohort consisted of all eligible patients with oligometastatic cancer treated with SBRT to spine or non spine bone metastases between years 2017 and 2021 at the OIL. Data on clinical, tumour and treatment characteristics were retrieved retrospectively using institutional medical records. Oligometastatic disease was classified according to ESTRO-EORTC recommendations (1). Kruskal-Wallis, Mann-Whitney tests, and multivariate logistic regression were used to analyse possible associations between the parameters. To estimate survival data, the Kaplan-Meier method was used.

Results:

Over a 5-year period, we treated 85 patients with 105 SBRT courses for spine (n=58, 55.2%) or non-spine (n=47, 44.8%) bone oligometastatic disease. The most common primary tumor histology was prostate cancer (n=37, 34.3%), followed by lung cancer (n=33, 30.6%), and breast cancer (n=24, 22.6%). According to the ESTRO-EORTC oligometastatic disease classification, the most frequent oligometastatic state was de novo (n=84, 80%), followed by repeat (n=12, 11.4%) and induced oligometastatic disease (n=9, 8.6%). SBRT was delivered in 1 x 16 – 24 Gy (32.4%), 3 x 9 – 10 Gy (7.6%) or 5 x 6 – 7 Gy (60%). Median PTV volume was 52.2 cm3 (range, 2.9 – 119 cm3) for spine metastases and 18.6 cm3 (range, 3.8 – 160.5 cm3) for non-spine metastases. Median follow-up after SBRT was 17.1 months (range, 3.3 – 58.8 months). Local progression after SBRT was found in 15 of 105 metastases (13.9%) and the median time to local progression was 7.0 months (range, 1.4 – 28.1 months). The 1-year and 2-year local control rates were 96% and 83%, respectively. Lung cancer primary tumor was associated with statistically significant lower 2-year local control rate (57%) in comparison to prostate cancer (90%; p=0.013) or breast cancer (92%, p=0.021). The 2-year local control did not differ between spinal and non-spinal bone metastases (79% vs. 89%, p=0.165), different fractionation schedules or the ESTRO-EORTC oligometastatic disease classification (p=0.932) (Figure 1). In the multivariate logistic regression, the only parameter associated with local progression following SBRT was the volume of the PTV (p=0.002). Thirty patients (28.6%) died after undergoing SBRT after a median of 10.5 months (range, 3.3 – 28.2). Median overall survival was not reached for de novo and repeat oligometastatic disease, and was 22.5 months (95% confidence interval, 7.5 – 36.6) for induced oligometastatic disease (Figure 2) (p=0.119). Acute toxicity grade 1 – 2 (CTCAE v.5.0) was observed in 28 (33.3%) patients and grade 3 in four (4.7%) patients. A total of six patients (7.1%) were impacted by late-grade toxicity grades 1-2, while three patients (3.5%) experienced grade 3 late-toxicity. During the observation period, no grade 4 or 5 acute or late toxicity was observed.