Spinal Cord Dose Tolerance to Stereotactic Body Radiation Therapy

Spinal cord tolerance data for stereotactic body radiation therapy (SBRT) were extracted from published reports, reviewed, and modelled. For de novo SBRT delivered in 1 to 5 fractions, the following spinal point maximum doses (Dmax) are estimated be associated with a 1% 5% risk of myelopathy (RM): 12.4 14.0 Gy fraction, 17.0 2 20.3 3 23.0 4 25.3 fractions. reirradiation reported factors lower RM include cumulative thecal sac equivalent dose fractions an alpha/beta (EQD22) Dmax ≤70 Gy; EQD22 ≤25 Gy, ratio ≤0.5, minimum time interval ≥5 months. Larger studies containing complete institutional cohorts dosimetric patients treated spine SBRT, without RM, required refine estimates. SummaryA review reports after was performed. This report presents several dose-response models, recommends limits cord, outlines standards future reporting clinical data. A Stereotactic metastases is emerging as standard care oligometastases,1Chang J.H. Gandhidasan S. Finnigan R. et al.Stereotactic ablative radiotherapy treatment oligometastases.Clin Oncol (R Coll Radiol). 2017; 29: e119-e125Abstract Full Text PDF PubMed Scopus (16) Google Scholar radioresistant histologies,2Kothari G. Foroudi F. Gill Corcoran N.M. Siva Outcomes cranial extracranial metastatic renal cell carcinoma: systematic review.Acta Oncol. 2015; 54: 148-157Crossref (57) or prior therapy, both sole modality3Mantel Flentje M. Guckenberger re-irradiation situation—a review.Radiat 2013; 8: 7Crossref postoperative setting.4Redmond K.J. Lo S.S. Soltys S.G. al.Consensus guidelines metastases: Results international survey.J Neurosurg Spine. 26: 299-306Crossref (46) The main benefit this technique ability escalate tumor volume while sparing adjacent organs at (OARs). At inception owing uncertainties regarding response extreme inhomogeneous hypofractionated there much variation practice among early adopters. Some applied traditional conservative within others assumed small volumes could tolerate greater long volumetric thresholds respected. There also considerable respect how delineated what structure limit being applied. These variations have persisted, uncertainty field “safe” dose/volume SBRT. With over decade worldwide experience initial spate (RM) cases adopters, Hypofractionation Treatment Effects Clinic (HyTEC) aims summarize current understanding dose, volume, outcome human specific image guided, (1-5 per fraction >6 Gy) Data estimates provided exposure (termed respectively). provides updated recommendations based on since American Association Physicists Medicine Task Group 101 (TG101) report.5Benedict S.H. Yenice K.M. Followill D. therapy: AAPM 101.Med Phys. 2010; 37: 4078-4101Crossref (1053) Several other potential spine-based toxicities such vertebral compression fracture6Sahgal A. Grosshans D.R. 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El-Mahdi A.M. period myelopathy.Int J Radiat Biol 1984; 10: 1109-1115Abstract (99) median series reviewed (Tables 2) 12 6 reirradiation. shortened likely reflects biological effect higher, more extreme, inherent SBRT.Table 1De that met inclusion criteria reviewSeriesNo. patientsDose structureMedian prescribed (range)/number (range)Median Dmax, GyMedian EQD22, follow-up, moNo. RMChang 201245Chang U.K. Cho W.I. Kim M.S. C.K. Lee D.H. Rhee C.H. Local control retreatment metastasis using radiotherapy; comparison group.Acta 2012; 51: 589-595Crossref (53) Scholar,∗The results only who row (instead full cohort original study).131Thecal sacMean 50.7/NSNSMean 48.68 ± 29.97Mean 23.70Daly 201142Daly M.E. Choi C.Y. Gibbs I.C. al.Tolerance radiosurgery: Insights hemangioblastomas.Int 2011; 80: 213-220Abstract Scholar19Cord20 (18-30)/1 (1-3)1 Fx: 22.7 (range, 17.8-30.9);2 Fx 22.0 21.3-26.6);3 21.9 19.7-25.4)1 140.17;2 71.5;3 50.92†Cumulative summary presented paper.33.71Gerszten 201253Gerszten P.C. 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Campbell Tseng C.L. al.Salvage in-field failure 93: 353-360Abstract (56) Scholar,§The same study broken into different rows.16Cord PRV (+1.5 mm)30 (20-35) (2-5)SBRT 24 (20-35)/ (1-5)NS21.9 (12.4-25.0)51.36.80Thibault rows.24Cord (24-35) (2-5)cEBRT: 22.5 (20-30); (20-30)/ (2-5)NS21.9 (17.5-26.7)73.96.80Abbreviations: cEBRT conventional external beam therapy; planning organ-at-risk volume; myelopathy.§ rows. Abbreviations: therapy. In addition symptoms, further supported by injury contrast-enhanced magnetic resonance imaging (MRI).8Wong Characteristic MRI findings low signal T1-weighted images, high T2-weighted focal contrast enhancement segment. Experiments rodents confirm intensity correlates histopathologically demyelination, edema, necrosis, postcontrast administration blood–spinal barrier disruption.8Wong histologic features demyelination necrosis typically confined white matter, although they pathognomonic injury.8Wong Other changes varying degrees vascular glial reaction. 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