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There is a lack of randomized evidence to guide the optimal approach for SABR in patients with pulmonary oligometastases. We conducted a randomized trial comparing single with multi-fraction SABR for patients with 1-3 pulmonary oligometastases. Herein, we report the extended follow-up survival outcomes of the Trans Tasman Radiation Oncology Group (TROG) 13.01 SAFRON II study.

TROG 13.01 SAFRON II was a multicentre unblinded randomized phase II trial across 13 centres in Australia and New Zealand. Enrolment was between 2015 and 2018, with minimum follow-up of 2 years. Extended follow-up was until Sep 2022. Participants had 1–3 oligometastases of <5cm diameter to the lung from any non-haematological malignancy, located away from central airways, ECOG 0-1, and all primary and extrathoracic disease controlled with local therapy. The interventions were either a single fraction of 28Gy (SF Arm) or four fractions of 12Gy (MF Arm) prescribed to the periphery (D99≥100%) of each oligometastasis. Participants were stratified by the number of metastases and histology (colorectal versus non-colorectal). Participants were not allowed systemic therapy during or after receipt of SABR until the time of progression. The primary outcome was grade 3 treatment related AEs (CTCAE v4.0) occurring within 1 year of SABR. Secondary survival outcomes included disease free survival (DFS) and overall survival (OS) were reported.

90 participants were randomized, with n = 87 treated for 133 pulmonary oligometastases (Figure 1). Median follow-up was 5.4 years. Median age was 68 years, 64% were male. The number of pulmonary oligometastases was 1 in 51 (59%), was 2 in 26 (30%) and 3 in 10 (11%). The most common histology was colorectal 41 (47%). The primary outcome measure of Grade 3 AEs within 1-year was not modified in the extended follow up. The grade 3 AEs [rate in the MF Arm and SF Arm were 3% [80% CI: 0-10] and 5% [80% CI: 1-13], p = 0.37. There was one grade 5 AE in the MF arm. In the overall cohort, the 3 and 5 year estimates (95% CIs) for OS were 70% (59-78) and 51% (39-61). Overall, the 3 and 5 year estimates (95% CIs) for DFS were 26% (18-36) and 22% (14-32). There were no significant differences between the MF and SF arms for OS (HR 1.1 [95% CI: 0.6-2.1], p = 0.77), or DFS (HR 1.0, [95% CI: 0.6-1.6], p = 0.99; Figure 2).

Figure 1: CONSORT Diagram

Figure 2: Efficacy outcomes after SABR comparing each arm

Kaplan-Meier curves illustrating Overall Survival (A) and Disease Free Survival (B).

In this patient population, where patients receive SABR in lieu of systemic therapy, SABR is associated with good long term oncological outcomes. Outcomes were similar in the MF and SF SABR arms.  Trial Registration: Clinicaltrials.gov ID:NCT01965223