Impact of cervicothoracic region stereotactic spine radiosurgery on adjacent organs at risk

OBJECTIVE Stereotactic radiosurgery (SRS) of the spine is a conformal method of delivering a high radiation dose to a target in a single or few (usually ≤ 5) fractions with a sharp fall-off outside the target volume. Although efforts have been focused on evaluating spinal cord tolerance when treating spinal column metastases, no study has formally evaluated toxicity to the surrounding organs at risk (OAR), such as the brachial plexus or the oropharynx, when performing SRS in the cervicothoracic region. The aim of this study was to evaluate the radiation dosimetry and the acute and delayed toxicities of SRS on OAR in such patients. METHODS Fifty-six consecutive patients (60 procedures) with a cervicothoracic spine tumor involving segments within C5-T1 who were treated using single-fraction SRS between February 2006 and July 2014 were included in the study. Each patient underwent CT simulation and high-definition MRI before treatment. The clinical target volume and OAR were contoured on BrainScan and iPlan software after image fusion. Radiation toxicity was evaluated using the common toxicity criteria for adverse events and correlated to the radiation doses delivered to these regions. The incidence of vertebral body compression fracture (VCF) before and after SRS was evaluated also. RESULTS Metastatic lesions constituted the majority (n = 52 [93%]) of tumors treated with SRS. Each patient was treated with a median single prescription dose of 16 Gy to the target. The median percentage of tumor covered by SRS was 93% (maximum target dose 18.21 Gy). The brachial plexus received the highest mean maximum dose of 17 Gy, followed by the esophagus (13.8 Gy) and spinal cord (13 Gy). A total of 14 toxicities were encountered in 56 patients (25%) during the study period. Overall, 14% (n = 8) of the patients had Grade 1 toxicity, 9% (n = 5) had Grade 2 toxicity, 2% (n = 1) had Grade 3 toxicity, and none of the patients had Grade 4 or 5 toxicity. The most common (12%) toxicity was dysphagia/odynophagia, followed by axial spine pain flare or painful radiculopathy (9%). The maximum radiation dose to the brachial plexus showed a trend toward significance (p = 0.066) in patients with worsening post-SRS pain. De novo and progressive VCFs after SRS were noted in 3% (3 of 98) and 4% (4 of 98) of vertebral segments, respectively. CONCLUSIONS From the analysis, the current SRS doses used at the Cleveland Clinic seem safe and well tolerated at the cervicothoracic junction. These preliminary data provide tolerance benchmarks for OAR in this region. Because the effect of dose-escalation SRS strategies aimed at improving local tumor control needs to be balanced carefully with associated treatment-related toxicity on adjacent OAR, larger prospective studies using such approaches are needed.