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Elective versus involved target volume definition of stereotactic spine radiosurgery for spinal metastases: A phase
Yi-Lun Chen1,2, Shih-Fan Lai1,3,4, Wen-Chi Yang1,3,5,4
1Division of Radiation Oncology, Department of Oncology, National Taiwan University Hospital, Taipei, Taiwan (Y.-L.C., S.-F.L., W.-C.Y., S.-L.L., F.-M.H.).
Background:
With the growing adoption of stereotactic spine radiosurgery (SSRS), precise target delineation is essential. The International Spine Radiosurgery Consortium (ISRC) has proposed contouring guidelines covering both the tumor and adjacent structures, termed the elective field (EF). We designed this randomized trial comparing EF and involved field (IF)-contouring strategy to determine which yielded the lowest protocol-specified failure rate.
Methods:
Patients with spinal metastases not requiring surgery were randomized 1:1 to receive 16 Gy in a single fraction via EF or IF SSRS. EF followed ISRC recommendations. IF comprised the gross tumor volume with an 8-mm isotropic intraosseous margin. We aimed to reject failure rates >10% at 6 months. Treatment failure was defined as grade ≥3 treatment-related toxicity or local progression.
Results:
Between August 2019 and May 2024, 106 patients (164 segments) were analyzed. Fifty-two and 54 patients were randomized to EF and IF, respectively. The median follow-up was 41.6 months. At 6 months, the cumulative incidence of treatment failure (CIF) met the acceptability criteria (per-patient: EF 3.8% vs IF 7.5%, P = .42). By 12 months, EF group showed low CIF, both per-patient (3.8% vs 13.5%) and per-segment (2.6% vs 11.8%). CIF curves differed significantly between groups (Gray's test, per-patient: P = .03, per-segment: P = .02). In the IF group, two-thirds of the out-of-field or marginal recurrences could be enclosed by the EF contouring strategy.
Conclusions:
EF and IF SSRS met the criteria for acceptable CIF at 6 months. With longer follow-up, EF demonstrated lower failure rates. ISRC contouring guidelines should be the standard practice.
