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Stereotactic body radiotherapy (SBRT) has rapidly gained acceptance in the radical treatment of oligometastatic disease (OMD), even if prospective evidence from clinical trials remains scarce and results from randomized phase III trials are still awaited. Patterns-of-care and survival of patients undergoing SBRT for OMD in the context of a coverage with evidence development (CED) program in Belgium are reported.

As of 2013, Belgian radiation oncology centers delivering SBRT were invited to participate in the prospective 'Innovative Radiotherapy Techniques' registration project, an initiative of the Belgian National Institute for Health and Disability Insurance (NIHDI), in exchange for temporary research funding. Eligible patients belonged to pre-determined target groups receiving SBRT for a primary tumor or for OMD, defined as a maximum of 3 metastatic lesions. ‘Standard’ vs. ‘non-standard’ indications were defined, the latter requiring enrollment in a formal clinical trial to be eligible for registration and financing. Real-life data on patient, disease and treatment characteristics were recorded in a registration module, available as an online application of the Belgian Cancer Registry. Survival was obtained through August 9^th, 2021.

Between 10/2013 and 12/2019, a total of 6,296 SBRT courses were registered in 20 of the 25 radiotherapy centers in Belgium, courses per center ranging between 21 and 951. After data cleaning, 5,675 courses concerning 4,841 patients were available for analysis. Of these, 2,790 pertained to OMD, with 1,484 (53%) being ‘standard’ lung metastases, 537 (19%) (para)spinal and 327 (12%) liver metastases. The ‘non-standard OMD’ group included the remaining 442 (16%) courses, with a dominance of lymph node (n=165, 37%) and non-spinal bone (n=248, 56%) metastases. Patients typically had a good performance status and most frequently only one metastatic lesion. Total dose, fractionation and techniques varied, but higher total doses and techniques evaluating/compensating tumor motion were more frequently used for lung and liver metastases than for the other indications. Overall survival was highest in case of ‘non-standard’ metastases, mostly pertaining to patients with primary prostate cancer, whereas liver metastases did worst. Major patient, disease and treatment characteristics, and survival, are shown in table 1; Kaplan-Meyer survival curves in Figure 1.

This national CED program prospectively evaluated SBRT implementation across Belgium. It shows that patients treated for OMD in the Belgian clinical practice were carefully selected. While variable, treatment characteristics and survival data conform to those previously reported in the literature. Together with data collection in ongoing clinical trials and other prospective cohorts such as OligoCare, these data allow to better understand and define the role of metastasis-directed radiotherapy in different OMD indications.