302 - Elective Target Stereotactic Spine Radiosurgery (SSRS) Reduces Risk of Long-Term Treatment Failure Compared to Involved Target SSRS: Final Analysis of A Prospective Randomized Phase II Trial

01:05pm - 01:15pm PT

Room 310-312

Presenter(s)

Feng-Ming Hsu, MD, PhD - National Taiwan University Cancer Center, Taipei, Taipei

Y. L. Chen¹, S. F. Lai^2,3, W. C. Yang^2,3, Y. F. Chen⁴, F. R. Xiao⁵, F. Y. Tsuang⁶, W. H. Lin⁷, and F. M. Hsu^2,3; ¹Division of Radiation Oncology, Department of Oncology, National Taiwan University Biomedical Park Hospital, Hsinchu, Taiwan, ²Division of Radiation Oncology, Department of Oncology, National Taiwan University Hospital, Taipei, Taiwan, ³Department of Radiation Oncology, National Taiwan University Cancer Center, Taipei, Taiwan, ⁴Department of Medical Imaging, National Taiwan University Hospital, Taipei, Taiwan, ⁵Department of Surgery, National Taiwan University Hospital and College of Medicine, Taipei, Taiwan, ⁶Department of Surgery, National Taiwan University Hospital, Taipei, Taiwan, ⁷Department of Orthopaedic Surgery, National Taiwan University Hospital, Taipei, Taiwan

Purpose/Objective(s):

Stereotactic spine radiosurgery (SSRS) has been rapidly adopted in clinics. To utilize SSRS, appropriate delineation of the target is important to radio-oncologists. The International Spine Radiosurgery Consortium (ISRC) has proposed delineation guideline to treat the tumor and adjacent spinal structures. Due to a lack of solid trials to support the proposal, we designed this randomized study comparing two SSRS treatment volumes to determine which results in the least protocol-specified treatment failure.

Materials/Methods:

Patients with unirradiated spine metastases not requiring surgery were enrolled and randomized 1:1 to receive elective (EF) or involved (IF) target radiosurgery with 16 Gy in 1 fraction. The elective target was defined as the spinal tumor with nearby anatomic classification according to the ISRC guideline. The involved target was limited to the spinal tumor with an isotropic 8-mm margin, but extraosseous expansion was not allowed. This study was designed to detect a protocol-specified treatment failure rate > 10% at a significance level of 0.05 (two-sided) and 90% power. Treatment failure was defined as the presence of = grade 3 toxicities or local progression indicative of surgery or re-irradiation.

Results:

Between August 2019 and May 2024, 106 patients were enrolled for SSRS to 164 spinal metastases. Majority of the tumors were located at thoracic spine (89 sites), followed by lumbar (42 sites), cervical (20 sites) and sacrum (13 sites). Most patients (89%) had lung cancer. Fifty-two patients and 54 patients were randomized to EF and IF, respectively. Median follow-up time was 41.6 months (IQR, 20.4–54.4 months). At 6 months, 2 patients in EF and 3 patients in IF arm experienced treatment failure. Cumulative incidence of treatment failure at 6- and 12-month between EF and IF arm were 3.8% versus 5.7% and 3.8% versus 11.6% (p=0.032), respectively. Median treatment failure-free survival was 40.8 months in EF arm and 21.7 months in IF arm. Overall survival at 6- and 12-month between EF and IF arm were 94.2% versus 88.7% and 86.3% versus 71.0% (p=0.14), respectively. Only two patients (one in each arm) experienced = grade 3 vertebral compression fracture and underwent vertebroplasty at 1.9 months and 21.6 months after SSRS, respectively.

Conclusion:

Both the elective and involved target SSRS met the pre-specified criteria at 6 months. With longer follow-up, EF might be the preferable SSRS target volume owing to its lower treatment failure rate. Delineation guideline proposed by ISRC should be the standard of care for SSRS.