A quantitative and comparative evaluation of stereotactic spine radiosurgery local control: proposing a consistent measurement methodology

Abstract

OBJECTIVE Stereotactic body radiotherapy (SBRT) is a precise and conformal treatment modality used in the management of metastatic spine tumors. Multiple studies have demonstrated its safety and efficacy for pain and tumor control. However, no uniform quantitative imaging methodology exists to evaluate response to treatment in these patients. This study presents radiographic local control rates post-SBRT, systematically compares measurements acquired according to WHO and Response Evaluation Criteria in Solid Tumors (RECIST) criteria, and explores the relationship to patient outcome. METHODS The authors performed a retrospective review of prospectively obtained data from a cohort of 59 consecutive patients (81 metastatic isocenters) treated with SBRT and followed with serial MRI scans. Measurements were performed by a neuroradiologist blinded to the patients’ clinical course. Local control status was determined according to both WHO and RECIST measurements, and agreement between the measuring methodologies was calculated and reported. RESULTS Eighty-one isocenters (111 vertebral bodies) were treated with SBRT. The mean treatment dose was 13.96 Gy and the median follow-up duration was 10.8 months, during which 408 MRI scans were evaluated with both WHO and RECIST criteria for each scan point. Imaging demonstrated a mean unidimensional size decrease of 0.2 cm (p = 0.14) and a mean area size decrease of 0.99 cm2 (p = 0.03). Although 88% of the case classifications were concordant and the agreement was significant, WHO criteria were found to be more sensitive to tumor size change. The local control rates according to WHO and RECIST were 95% and 98%, respectively. CONCLUSIONS Although WHO volumetric measurements are admittedly superior for tumor size measurement, RECIST is simpler, reproducible, and for the first time is shown here to be comparable to WHO criteria. Thus, the application of RECIST methodology appears to be a suitable standard for evaluating post-SBRT treatment response. Moreover, using comprehensive and consistent measuring approaches, this study substantiates the efficacy of SBRT in the treatment of spine metastases.

Editorial. Assessing treatment response following stereotactic body radiotherapy for spinal metastases

“…12 The paper by Harel and colleagues in this edition of Neurosurgical Focus addresses the need for a simple, reproducible, quantitative method of assessing local treatment response derived from widely available imaging modalities. 13 They sought to validate and compare the WHO and RECIST tumor response criteria for spinal column metastases following SBRT by using traditional MRI. Their cohort included 59 patients with spinal column metastases representing 111 diseased vertebral bodies treated with SBRT at 81 isocenters.…”

“…Their cohort included 59 patients with spinal column metastases representing 111 diseased vertebral bodies treated with SBRT at 81 isocenters. 13 They described a straightforward technique of measuring pretreatment tumor dimensions in three orthogonal planes: anteriorposterior, transverse, and cranial-caudal. The largest of these measurements was used for RECIST criteria, and the two largest were used to calculate WHO criteria.…”

“…They observed local control rates of 95% and 98% using WHO and RECIST criteria, respectively, at a median follow-up of 10.8 months, and demonstrated a statistically significant agreement between the two methods. 13 Due to simplicity in obtaining unidimensional measurement, they favored adopting RECIST as a uniform strategy for assessing treatment response for spinal column metastases following SBRT. They posit that standardization will benefit data integration and have positive downstream effects on clinical trials and outcomes.…”

“…They posit that standardization will benefit data integration and have positive downstream effects on clinical trials and outcomes. 13 The inherently complex nature of the spinal column and its associated tumors as well as the level of variability present in MRI technique serves to complicate current anatomical assessment methods. The use of detailed volumetric analysis, the standard for evaluating certain other pathologies such as intracranial tumors, is in its infancy for use with spinal column metastases.…”

“…These include a lack of imaging standardization between centers, the labor-intensive nature of tumor contouring, and the present difficulty in developing software to effectively resolve issues related to spinal instrumentation. 13 The role of advanced imaging modalities is also of interest in evaluating tumor progression. A novel method of assessing treatment response, PERCIST (PET Response Criteria in Solid Tumors) is not based on anatomical response but rather on changes in tumor metabolic activity as measured on FDG-PET.…”