Session Item

Stereotactic ablative radiotherapy (SABR) in case of multiple oligometastases represents a challenge approach for clinical and technical reasons. We evaluated the outcome of a large sample of patients affected by 3 to 5 oligometastases treated with SABR.

We included patients treated with single course SABR on 3 to 5 extracranial oligometastases. Concomitant systemic treatment was allowed. All patients were treated with the volumetric modulated arc therapy (VMAT) technique. End-points of the analysis were overall survival (OS), progression free survival (PFS) and toxicity.

136 patients were treated from 2012 to 2020 on 450 oligometastases. Most common primary tumors were colorectal cancer (44.1%) and lung cancer (11.8%). Fifty-four (39.7%) patients had previous local treatment, while 22 (16.2%) patients received ≥ 3 lines of systemic therapies before SABR. A total of 3, 4 and 5 lesions were treated simultaneously in 102 (75.0%), 26 (19.1%), and 8 (5.9%) patients, respectively. After a median follow-up of 25.0 months, OS rates at 1 and 2 years were 81.6% and 55.7%. Performance status (p=0.022) and minimum EQD2 (p=0.032) were independent risk factors for OS. Median OS was 27.7 months with EQD2 < 70 Gy vs 47.5 months with ≥ 70 Gy. Median PFS was 8.06 months, with 1 and 3 year rates of 34.8% and 6.5%. Previous systemic therapy (p=0.002), non-liver metastases (p=0.012), concomitant systemic therapy (p=0.002) and minimum EQD2 (p=0.002) were correlated with PFS. In terms of toxicity, no grade 3 or higher side effects were reported in both acute and late settings.

We demonstrated the safety of SABR when treating large volume oligometastatic disease. Moreover, SABR minimum dose seems to have an impact on the overall disease control and survival of patients affected by 3 to 5 oligometastases.