40 Gray in 5 Fractions for Salvage Re-Irradiation of Spine Lesions Previously Treated with Stereotactic Body Radiotherapy

Purpose/Objective(s)

This is a retrospective single-center analysis of the safety and efficacy of re-irradiation to 40 Gray (Gy) in 5 fractions in patients previously treated with stereotactic body radiotherapy (SBRT) to the spine.

Materials/Methods

We identified 62 consecutive patients with various solid malignancies treated between January 2016 and December 2021 to 40 Gy in 5 fractions regardless of dose and fractionation at the first course of SBRT. Patients were followed clinically and with routine imaging. Acute (≤3 months) and late (>3 months) toxicities were assessed according to CTCAE v5.0. Local control was defined as absence of progression within the treated target volume. Time to progression was calculated from date of completion of SBRT to the date of an imaging study indicating progression. The probability of local progression before death was estimated using a cumulative incidence curve, and death without local progression was considered a competing risk.

Results

Most patients had oligometastatic disease (53.2%) and treated to the thoracic spine (51.6%). The most common fractionation regimen in the first course of SBRT was 27 Gy in 3 fractions, and the median time to re-irradiation was 13.1 months (range, 2.4-86.9 months). Twenty-four patients (38.7%) had surgery before re-irradiation. At time of simulation, 49 patients (79%) had epidural disease, including 19, 13, 12 and 5 patients with epidural spinal cord compression (ESCC) scale 1a, 1b, 1c and 2, respectively. Accordingly, myelogram simulations were performed in 82.2% of patients. Both the vertebral body and posterior elements were treated in 93.5% of patients. All early toxicities were low grade, apart from one case of grade 3 fatigue, one case of grade 3 diarrhea and one case of grade 3 pneumonitis. Five patients experienced a pain flare (8.1%). Two thirds of patients who reported pain at baseline, achieved improvement (33%) or complete resolution of pain (33%). About 40% of patients had at least a partial response in magnetic resonance imaging (MRI). At a median follow up time of 11.9 months (range, 1.8- 39.6 months), six patients (9.7%) suffered local progression. The median time to progression was 4.1 months (range, 1.93-13.8 months). The estimated incidence rate of local progression before death at 6-months and 12-months was 7%. Five patients (8.1%) developed radiation-related neuropathy (grade 1, 2 and 3 in two, one and two cases, respectively). No patient suffered grade 4 or higher late toxicity. The vertebral compression fracture rate was 16%. Three patients (4.8%) eventually underwent kyphoplasty and two patients underwent surgery (3.2%) for vertebral fractures.

Conclusion

Re-irradiation with 40 Gy in 5 fractions seems safe and effective for the salvage of lesions progressing after a previous course of SBRT in a cohort of patients with extensive disease involvement. Prospective randomized trials are needed to determine the optimal dose and fractionation in this clinical scenario.