We sought to characterize outcomes from a large institutional database of patients treated with 3-fraction spine stereotactic body radiation therapy (SBRT) after prior overlapping RT. The primary outcome of interest was local failure (LF) in the treated lesion, defined based on MRI. We also characterized toxicities such as vertebral compression fracture (VCF) and radiation myelitis (RM). There were 83 patients treated to 87 spinal lesions between 2014-2023. Median follow-up was 14.2 (interquartile range (IQR) 6-29.4) months and median overall survival was 20.5 (95% confidence interval (CI) 16.5-29.9) months. Most lesions were treated with 27 Gy in 3 fractions (n=78; 90%). Most lesions had been treated with prior conventionally fractionated RT (59%), and the most common histology was prostate cancer (n=15; 17%). The 1- and 2-year LF rate was 8.4% (95% CI 3.7-16%) and 15% (95% CI 8.1-24%), respectively. On univariable analysis, lower minimum dose (DMin) to the planning target volume (PTV) (HR 0.85, 95% CI 0.74-0.99, p=0.03) and colorectal, cholangio-, or hepatocellular carcinoma histology (HR 5.6, 95% CI 1.11-28.4, p=0.037) were associated with risk of LF. There was 1 case of RM (1.3%) and 5 cases (5.5%) of VCF. Re-irradiation with spine SBRT in 3 fractions appears safe and is associated with a 2-year local control rate of 85%. Lower PTV DMin and gastrointestinal histology were associated with increased risk of LF. Further work is needed to identify the optimal dose-fractionation regimen for re-irradiation with spine SBRT.

Spinal metastases may cause pain, neurological compromise, paraplegia, and limb movement disorders; their management requires a comprehensive approach. Alongside systemic anti-tumor therapies, focal interventions such as radiotherapy, bone-modifying agents, and surgery are crucial for slowing disease progression and managing pain in spinal metastases. However, substantial variations exist in radiotherapy regimens for spinal metastases. In this study, we aimed to investigate the safety and efficacy of hypofractionated radiation therapy (HFRT) regimens at our hospital, specifically to evaluate pain relief and incidence of re-irradiation after HFRT. In this retrospective study, data from 58 patients diagnosed with spinal metastasis who received HFRT (4.5-10Gy * 3-7F) at our center between December 2017 and June 2022 were analyzed. All patients were followed up from the initiation of HFRT to either death or their last follow-up visit. Degree of pain was assessed using the numeric rating scale (NRS) before and after 1 month of HFRT. A multivariate Cox regression model was established to identify the independent risk factors for prognostic analysis of spinal metastasis. HFRT could effectively manage pain in patients with spinal metastasis. The pain scores were significantly decreased after HFRT (3.43 vs. 1.5, p < 0.001), with 84.5% patients experiencing improved pain relief 1 month after radiotherapy. No cases of radiation myelitis were observed during the follow-up period. Furthermore, the incidence of re-radiotherapy was significantly increased in patients with spinal metastases who received moderate HFRT (< 5 Gy/day) (p = 0.01, HR = 0.43). HFRT significantly reduced pain scores and reirradiation rates without increasing radiation myelitis incidence for spinal metastases.

Reirradiation of spinal metastases using stereotactic body radiation therapy (SBRT) presents clinical challenges, with limited patient outcomes data to guide decision-making. We report a retrospective, single-institutional experience of 107 lesions treated in 91 patients. Of these, 88 (72%) lesions were initially irradiated with conventional radiation therapy (median equivalent dose of 33 Gy to the target, IQR, 23-35 Gy) with a median time to reirradiation of 12 months (IQR, 4-21 months). For reirradiation, most lesions received either 1 fraction (18-24 Gy) or 3 fractions (30-36 Gy) of SBRT. The median equivalent dose in 2 Gy fractions was 38 Gy (IQR, 30-41 Gy), 27 Gy (22-36 Gy), and 65 (54-73 Gy) for previous courses, reirradiation, and cumulatively, respectively. At 1 year, overall survival was 61% with a cumulative incidence of local failure at 12% and vertebral compression fracture at 9% considering death as a competing risk. None of the 79 treated lesions at L1 or above developed radiation myelitis, but 5 patients developed chronic peripheral neuropathy. In our analysis, most adverse events or local failures occur within the 2 years after retreatment. These findings demonstrate the safety and effectiveness of spine reirradiation with SBRT.

Conventional external beam radiotherapy (cEBRT) is effective for managing symptomatic bone metastases and continues to be in demand despite advances in stereotactic body radiotherapy. This review provides an overview of cEBRT for bone metastases, with a focus on the following: (1) Initial palliative radiotherapy: randomized controlled trials and meta-analyses have shown that single-fraction cEBRT at 8 Gy is as effective as multifractionated cEBRT for reducing pain due to bone metastases. Single-fraction cEBRT at 8 Gy may be a reasonable option for bone metastases with neuropathic pain in consideration of the burden on patients. The efficacy of radiotherapy for preventing skeletal-related events in bone metastases remains unclear. Prophylactic fixation followed by radiotherapy is recommended for long-bone metastases at high risk of fracture. (2) Palliative reirradiation: reirradiation is indicated for patients with insufficient pain relief or pain progression after initial radiotherapy for bone metastases. In palliative reirradiation for spinal metastases, the tolerance dose of the spinal cord needs to be carefully considered due to the risk of radiation myelitis. (3) Treatment strategies for metastatic spinal cord compression (MSCC) or spinal bone metastases with instability: treatment decisions for MSCC, including radiotherapy or decompression surgery followed by radiotherapy, need to be carefully considered by a multidisciplinary team, including radiation oncologists and orthopedic surgeons. Moderate-dose corticosteroids (dexamethasone bolus of 10-16 mg) are recommended in combination with radiotherapy for MSCC. Spinal instability caused by spinal bone metastases is an indication for fixation surgery, and postoperative radiotherapy needs to be considered.

Stereotactic body radiation therapy (SBRT) for spinal metastases improves symptomatic outcomes and local control compared to conventional radiotherapy. Treatment failure most often occurs within the epidural space, where dose is constrained by the risk of radiation myelitis (RM). Current constraints designed to prevent RM after spine SBRT are derived from limited data. To characterize the risk of RM after spine SBRT and to update the dosimetric constraints for preventing it. This cohort study was conducted in a single tertiary cancer care center with patients treated for spinal metastases from 2014 to 2023. All included participants had undergone spine SBRT, had a minimum of 1-month follow-up with magnetic resonance imaging (MRI), a maximal cord dose to a voxel (Dmax) greater than 0 Gy, and no overlapping prior radiotherapy. In all, 2051 patients received SBRT to 2835 spinal metastases (levels C1-L2) during the study period. Three-fraction spine SBRT to a prescription dose of 27 to 36 Gy. RM defined as radiographic evidence of spinal cord injury in the treatment field, classified as grade (G) 1 to G4 or G3 to G4 per the Common Terminology Criteria for Adverse Events, version 5.0. Multiple dosimetric parameters of the true spinal cord structure were assessed for an association with risk of RM to determine the important covariates associated with this toxicity. The analysis included 1423 patients (mean [SD] age, 61.6 [12.9] years; 695 [48.8%] females and 728 [51.1%] males) who received SBRT for 1904 spinal metastases. Among them, 30 cases of RM were identified, 19 of which were classified as G3 to G4. Two years after SBRT, the rate of G1 to G4 RM was 1.8% (95% CI, 1.2%-2.5%) and the rate of G3 to G4 RM was 1.1% (95% CI, 0.7%-1.7%). The minimum dose to the 0.1 cm3 of spinal cord receiving the greatest dose (D0.1cc) was the most important covariate on univariable cause-specific hazards regression for RM (for G3 to G4: hazard ratio, 2.14; 95% CI, 1.68-2.72; P < .001). A true cord D0.1cc of 19.1 Gy and Dmax of 20.8 Gy estimated a 1.0% risk (95% CI, 0.3%-1.6% and 0.4%-1.6%, respectively) of G3 to G4 RM 2 years after SBRT. The findings of this cohort study indicate that a cord (myelogram or MRI-derived) D0.1cc constraint of 19.1 Gy and a Dmax constraint of 20.8 Gy correspond with a 1.0% risk of G3 to G4 RM at 2 years.