Defining the Role of SABR in Head and Neck Cancer: Results From a Multi-institutional Delphi Consensus

The role of SABR in head and neck cancer remains uncertain. Historically, it has been used mainly for reirradiation, and its application in other clinical scenarios has expanded with recent advances.

To develop an international expert consensus on indications, technical parameters, and clinical application of head and neck SABR using a modified Delphi process.

A three-round modified Delphi process was conducted between July 2021 and January 2023. Radiation oncologists with experience in head and neck SABR were invited to participate. Round 1 consisted of open-ended questions. Rounds 2 and 3 involved rating agreement with 103 statements addressing indications, contraindications, planning, dose and fractionation, toxicity mitigation, systemic therapy integration, and follow-up. Consensus was defined as ≥75% agreement, and major agreement as 65% to 74%.

Seventeen of 26 invited experts (65.4%) completed all rounds, with representation from North America, Europe, and Asia-Oceania. Of the 103 statements, 56 (54.3%) reached consensus, and 12 (11.7%) achieved major agreement. Consensus supported SABR for reirradiation of small isolated recurrences, unresectable tumors, or second primaries in previously irradiated fields, and oligometastatic lesions in untreated patients. Use in local palliation and in patients unfit for standard fractionation within a clinical trial also met consensus. No consensus was reached for postoperative SABR, including its use for positive margins or extranodal extension, nor for SABR boost in first-course treatment. Technically, consensus favored volumetric modulated arc therapy, tight planning target volume margins of 2 to 3 mm, multimodality imaging (thin-slice computed tomography, magnetic resonance imaging, and positron emission tomography/computed tomography), and daily volumetric imaging with physician verification. Clinical target volume expansion was discouraged, and elective nodal irradiation was not recommended. Every-other-day fractionation and dose reduction near critical structures were endorsed. Consensus emphasized counseling on key toxicities and supported imaging at 2 to 3 months post-SABR. No consensus was reached on systemic therapy integration.

This multi-institutional Delphi study provides expert-derived recommendations reflecting the current state of head and neck SABR practice and identifies priorities for future research.