title: A model for quantitative changes in the magnetic resonance parameters of muscle in children after therapeutic irradiation.
abstract: OBJECTIVE
  This study aimed to develop objective models of radiation effects on musculature in children with soft tissue sarcoma using treatment dosimetry and clinical and quantitative magnetic resonance imaging (MRI) parameters that may be used to guide treatment planning or predict side effects.
  
  
  METHODS
  In the initial 13 patients undergoing external beam radiation therapy (RT) on a Phase II study of conformal or intensity-modulated RT for the treatment of soft tissue sarcoma approved by an Institutional Review Board, we evaluated quantitative MRI changes in the musculature to assess radiation-related treatment effects. Patients with soft tissue sarcoma, including Ewing's sarcoma, had quantitative T1, T2 and dynamic enhanced MRI (DEMRI) performed before, during (Week 4) and after RT (Week 12). Regions of interest were selected in consistent locations within and outside the high-dose regions (on ipsilateral and contralateral sides when available). Mean RT dose, T1, T2 and DEMRI parameters were calculated and modeled using a mixed random coefficient dose model.
  
  
  RESULTS
  The mean doses to the high- and low-dose regions were 56.4 Gy (41.8-75.3 Gy) and 13.0 Gy (0.1-37.5 Gy), respectively. Compared with tissues distant from the tumor bed, maximal enhancement was significantly increased in tissues adjacent to the tumor/tumor bed prior to RT (60.6 vs. 44.2, P=.045) and remained elevated after 12 weeks. T1 was significantly elevated in tissues adjacent to the tumor bed prior to RT (942.4 vs. 759.0, P=.0078). The slope of longitudinal change in T1 was greater for tissues that received low-dose irradiation than those that received high-dose irradiation (P=.0488). The effect of dose on the slope of T2 was different (P=.0333) when younger and older patients are compared.
  
  
  CONCLUSIONS
  Acute affects of irradiation in muscle are quantifiable via MRI. These models provide evidence that quantifiable MRI parameters may be correlated with patient parameters of radiation dose and clinical factors including patient age. Long-term follow-up will be required to determine if acute changes correlate with clinically significant late effects.
authors.affiliation: Division of Radiation Oncology, Department of Radiological Sciences, St. Jude Children's Research Hospital, and Department of Pediatrics, University of Tennessee School of Medicine, Memphis, TN 38105-2794, USA. matthew.krasin@stjude.org
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Krasin
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Xiong
authors.forename: Wilburn E
authors.initials: WE
authors.lastname: Reddick
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Ogg
authors.forename: Fredric A
authors.initials: FA
authors.lastname: Hoffer
authors.forename: Beth
authors.initials: B
authors.lastname: McCarville
authors.forename: Sue C
authors.initials: SC
authors.lastname: Kaste
authors.forename: Sheri L
authors.initials: SL
authors.lastname: Spunt
authors.forename: Fariba
authors.initials: F
authors.lastname: Navid
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Davidoff
authors.forename: Lingqing
authors.initials: L
authors.lastname: Zhang
authors.forename: Larry E
authors.initials: LE
authors.lastname: Kun
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Merchant
mesh_terms: D002648:Child; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D019042:Muscle Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D018482:Muscle, Skeletal / Q000473:pathology / Q000528:radiation effects*; D011832:Radiation Injuries / Q000175:diagnosis*; D012509:Sarcoma / Q000473:pathology / Q000532:radiotherapy*