Session Item

Reports from recent years suggest a more aggressive approach for oligometastatic disease (OMD) may prolong overall survival. SOFT is a multicenter, phase II trial investigating the safety and efficacy of MR-guided stereotactic body radiotherapy (SBRT) of infra-diaphragmatic soft tissue metastases in patients with OMD (clinicaltrials.gov ID NCT04407897). The primary endpoint is severe toxicity rate within the first year. We report the baseline characteristics and target doses for the first 100 patients included in the trial.

Patients with OMD (≤ 5 metastases) or oligo-progressive disease (OPD) (≤ 3 metastases) are eligible for inclusion at four centers. Our strategy is to pursue safe SBRT for all metastatic sites by heterogeneous dose prescription, where organs at risk (OAR) constraints are prioritized over target coverage. Doses of 45 Gy/3 fractions (F), 50 Gy/5 F or 60 Gy/8 F are prescribed to the GTV, with 67% coverage of the PTV. Clinicians- and patient-reported toxicity, along with efficacy measures are registered in a Redcap database. Radiotherapy data are imported to the “Danish national radiotherapy data bank (DcmCollab)” for analysis.

The study started the inclusion of patients in October 2019. By November 2020, the primary goal was reached (61 patients recruited). The protocol was amended due to excess drop-out within the first year of follow-up and the recruitment population was increased to a total of 120 patients. All patients are expected to be included by the end of December 2021. In the first 100 patients, a total of 122 targets have been treated with 111 treatment plans. Prostate -, lung- and colorectal cancer are the most dominant primary diagnoses among the population (Table 1). Most targets have been in the liver (42%), but lymph nodes (30%) and adrenal glands (14%) also constitute a considerable part of the treated targets (Table 1). Most targets (86%) have been treated with the prescription dose per protocol, whereas in 14% of the targets another prescription was chosen (Table 2). Targets in the liver were larger than non-liver (mean GTV volume = 23.0 cm³ vs. 13.3 cm³, P< 0.01 Mann-Whitney Test). Achieved target coverage did not seem to be influenced by target location (liver vs. non-liver).

The SOFT trial is successfully recruiting patients. The preliminary dosimetric results on the first 100 patients suggest that ablative doses can be achieved for high-risk targets both inside and outside the liver. With continued effort to collect high-quality protocol data, we hope to gain more experience in the referral pattern and clinical outcome of patients with OMD. The SOFT protocol adheres to well-defined dose prescriptions, and here the first step toward collecting clear and consistent data on delivered target dose has been initiated.