Introduction: As spinal cord tolerance often precludes reirradiation with conventional techniques, local recurrence of spinal bony metastases within a previously irradiated field presents a treatment challenge.
Methods: We reviewed the treatment plans of 10 patients with spine metastases (15 spinal segments) who initially received conventional external beam radiation (EBRT). All were reirradiated with single-fraction SBRT (16Gy) at or above the L2 vertebral body with the spinal cord itself verified by MRI imaging at the treatment level.
Gross tumor was contoured as the planning target volume; no additional margins were used. Spinal cord dose-volume histogram (DVH) endpoints were constructed, keeping D0.35 (dose to 0.35cc of spinal cord volume) <10Gy, D1.2 <8Gy and any cord point max dose (Pmax) <14Gy. The biologically effective doses (BED) using alpha/beta = 2Gy for late spinal cord toxicity were calculated and normalized to a 2-Gy equivalent dose (nBED=Gy2/2).
Results: SBRT was given at median 7 months (range,2-36) after conventional palliative radiotherapy. Median distance from the tumor to spinal cord surface was 3.4mm (range,1.3-9.0). Seven lesions abut =180° of the spinal canal circumference. Dose prescribed to 86% isodose (range 55-92%) targeting median tumor volume of 7.3-cc (range,3--74-cc). The initial conventional radiotherapy nBED ranged from 30 to 45Gy2/2 (median 37.5Gy2/2). The SBRT reirradiation cord (P max) nBED ~42Gy2/2. The mean total (Pmax) nBED was approximately 79.5 Gy2/2. Percentage of the total (Pmax) nBED accounted for by the SBRT (Pmax) nBED were 50% to 67%. After median post-SBRT follow-up of 10 months, no radiation-induced myelopathy or radiculopathy has occurred.
Conclusions: SBRT given at least 7 months after conventional palliative radiotherapy with a reirradiation spinal cord (Pmax) nBED=42Gy 2/2 appears to be safe provided the total (Pmax) nBED does not exceed approximately 79 Gy2/2, and the SBRT cord (Pmax) nBED comprises no more than approximately 60% of the total nBED.
Patient Care: Patients can be aided with the use of SBRT given after conventional palliative radiotherapy to the spinal cord.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Describe the importance of reirradiation to the spinal cord with the use of SBRT.
2) Discuss, in small groups, SBRT to the spinal cord after conventional palliative radiotherapy.
3) Identify an effective treatment for local recurrence of spinal bony metastases.