1-year efficacy results after MR-guided risk-adapted stereotactic radiotherapy of infra-diaphragmatic oligometastases in a multicenter phase II trial.

Background And Purpose: The SOFT (Stereotactic ablative radiotherapy of infra-diaphragmatic sOFT tissue metastases) trial assesses the safety and efficacy of risk-adapted MR-guided stereotactic ablative radiotherapy (SABR) of infra-diaphragmatic soft tissue metastasis in patients with oligometastatic disease (OMD) (clinicaltrials.gov ID NCT04407897). This paper reports the one-year efficacy analysis and evaluates associations between local control (LC) and clinical and dosimetric parameters.

Materials And Methods: This investigator-initiated, multicenter, single-arm, phase 2 study recruited patients from four MR-linac centers in Denmark and the US. Patients with De novo or recurrent OMD with ≤5 metastases in ≤3 organs and patients with induced OMD or oligoprogressive disease (OPD) with ≤3 metastases were eligible. Fractionation schemes were 45-75 Gy in 3-8 fractions.

Results: The trial included 121 patients with 147 oligometastatic lesions, primarily in the liver (41 %), lymph nodes (35 %), or adrenal glands (14 %). The median follow-up time was 13.0 months, interquartile range (IQR) (11.7,13.7) months. The 1-year LC rate was 89 %, 95 % confidence interval (CI) (83,94 %). We did not observe any statistically significant associations between LC and clinical and dosimetric parameters. The median progression-free survival was 7.1 months, 95 % CI (6.0,9.4). One- and two-year overall survival was 82.6 %, 95 % CI (76.2 %,89.7 %), and 65.1 %, 95 % CI (56.4 %,75.3 %). Sixty-one patients (50 %) were kept off systemic therapy throughout the one-year follow-up.

Conclusion: In our study, treatment with risk-adapted, MR-guided SABR resulted in a high one-year local control and survival rate and could keep half of the patients off systemic therapy within the first year of follow-up.