title: Lhermitte's Sign following VMAT-Based Head and Neck Radiation-Insights into Mechanism.
abstract: OBJECTIVE
  We observed a number of patients who developed Lhermitte's sign (LS) following radiation to the head and neck (H/N), since instituting volumetric modulated arc therapy (VMAT). We aimed to investigate the incidence of LS following VMAT-based RT without chemotherapy, and determine the dosimetric parameters that predict its development. We explored whether the role of inhomogeneous dose distribution across the spinal cord, causing a "bath-and-shower" effect, explains this finding.
  
  
  METHODS
  From 1/20/2010-12/9/2013, we identified 33 consecutive patients receiving adjuvant RT using VMAT to the H/N without chemotherapy at our institution. Patients' treatment plans were analyzed for dosimetric parameters, including dose gradients along the anterior, posterior, right, and left quadrants at each cervical spine level. Institutional Review Board approval was obtained.
  
  
  RESULTS
  5 out of 33 (15.2%) patients developed LS in our patient group, all of whom had RT to the ipsilateral neck only. LS patients had a steeper dose gradient between left and right quadrants across all cervical spine levels (repeated-measures ANOVA, p = 0.030). Within the unilateral treatment group, LS patients received a higher mean dose across all seven cervical spinal levels (repeated-measures ANOVA, p = 0.046). Dose gradients in the anterior-posterior direction and mean doses to the cord were not significant between LS and non-LS patients.
  
  
  CONCLUSIONS
  Dose gradients along the axial plane of the spinal cord may contribute to LS development; however, a threshold dose within the high dose region of the cord may still be required. This is the first clinical study to suggest that inhomogeneous dose distributions in the cord may be relevant in humans. Further investigation is warranted to determine treatment-planning parameters associated with development of LS.
authors.affiliation: Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai Hospital, New York, New York, United States of America.
authors.forename: Huaising C
authors.initials: HC
authors.lastname: Ko
authors.affiliation: Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai Hospital, New York, New York, United States of America.
authors.forename: Allison R
authors.initials: AR
authors.lastname: Powers
authors.affiliation: Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai Hospital, New York, New York, United States of America.
authors.forename: Ren-dih
authors.initials: RD
authors.lastname: Sheu
authors.affiliation: Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai Hospital, New York, New York, United States of America; Department of Radiation Oncology, University of Rochester Medical Center, Rochester, New York, United States of America.
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Kerns
authors.affiliation: Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai Hospital, New York, New York, United States of America.
authors.forename: Barry S
authors.initials: BS
authors.lastname: Rosenstein
authors.affiliation: Department of Neurology, Icahn School of Medicine at Mount Sinai Hospital, New York, New York, United States of America.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Krieger
authors.affiliation: Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai Hospital, New York, New York, United States of America; Department of Radiation Oncology, Mount Sinai at Beth Israel Medical Center, New York, New York, United States of America; Department of Radiation Oncology, Albert Einstein School of Medicine at Montefiore Medical Center, New York, New York, United States of America.
authors.forename: Waleed F
authors.initials: WF
authors.lastname: Mourad
authors.affiliation: Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai Hospital, New York, New York, United States of America; Department of Radiation Oncology, Mount Sinai at Beth Israel Medical Center, New York, New York, United States of America.
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Hu
authors.affiliation: Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai Hospital, New York, New York, United States of America.
authors.forename: Vishal
authors.initials: V
authors.lastname: Gupta
authors.affiliation: Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai Hospital, New York, New York, United States of America.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Bakst
mesh_terms: D000368:Aged; D002294:Carcinoma, Squamous Cell / Q000473:pathology / Q000532:radiotherapy; D005260:Female; D006258:Head and Neck Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011832:Radiation Injuries / Q000175:diagnosis*; D011874:Radiometry; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000528:radiation effects*; D014057:Tomography, X-Ray Computed