2614 - Clinical Efficacy and Safety Evaluation of Moderately Hypofractionated Radiotherapy with Simultaneous Integrated Boost (MHRT-SIB) for Spinal Metastases: A Retrospective Study

Purpose/Objective(s): This study evaluated symptom relief, local control, and skeletal-related events (SREs) following moderately hypofractionated radiotherapy using simultaneous integrated boost (MHRT-SIB) in patients with spinal metastases, while exploring the technique's potential for dosimetric optimization.

Materials/Methods: This retrospective study included 27 patients with spinal metastases, primarily originating from breast and lung cancer, treated with MHRT-SIB at a single institution between July 2021 and November 2023. Target volumes were defined as follows: Gross tumor volume (GTV) included all CT/MRI-visible tumors. Clinical Target Volume (CTV) was contoured by expanding the GTV with an appropriate margin, encompassing the radiographically involved vertebral body and adjacent osseous structures. Planning Gross Tumor Volume (PGTV) and Planning Target Volume (PTV) were generated using a 5 mm isotropic expansion from GTV and CTV, with manual contour modifications to maintain spinal cord dose constraints (Dmax = 45 Gy). Volumetric modulated arc therapy (VMAT) or intensity-modulated radiotherapy (IMRT) with SIB plans were designed. Prescription doses were: PTV 30 Gy/10 fx (3 Gy/fx, BED = 39 Gy₁₀) and PGTV SIB 40 Gy/10 fx (4 Gy/fx; BED = 56 Gy₁₀) or 48 Gy/12 fx (4 Gy/fx; BED = 67.2 Gy₁₀). Primary endpoints analyze pain relief (Numerical Rating Scale), neurological function improvement (Frankel Grade), and skeletal-related event incidence; secondary endpoints include local control assessed via MRI/CT imaging.

Results: With a median follow-up of 9 months (range 3-42), 19 out of 27 patients had pain before radiation therapy. The median time to pain relief was 1 month, with an effective pain relief rate of 84.2% (16/19). Among them, 31.6% (6 patients) achieved complete pain relief, 52.6% (10 patients) had partial relief, and 15.8% (3 patients) experienced no relief. Neurological dysfunction was present in 15 patients before treatment, with a median relief time of 2–3 months. The effective neurological relief rate was 60.0% (9/15), including complete relief in 13.3% (2 patients), partial relief in 46.7% (7 patients), and no improvement in 40.0% (6 patients). Local recurrence occurred in three patients (11.1%), and no skeletal-related events (SREs), including pathologic fractures, radiation myelitis, or osteonecrosis, were observed.

Conclusion: This study demonstrates that MHRT-SIB is an effective treatment for spinal metastases, offering significant pain relief, neurological improvement, and local tumor control. Additionally, no skeletal-related events (SREs) were observed. Multicenter prospective trials are needed to confirm the efficacy of MHRT-SIB and refine dose regimens for spinal metastases.