Abstract
Radiation necrosis, for which abnormal WM enhancement is a hallmark, is an uncommon complication of craniospinal irradiation in children with medulloblastoma. The magnetization transfer ratio measures macromolecular content, dominated by myelin in the WM. We investigated whether the pretreatment supratentorial (nonsurgical) WM magnetization transfer ratio could predict patients at risk for radiation necrosis after radiation therapy for medulloblastoma. Ninety-five eligible patients with medulloblastoma (41% female; mean age, 11.0 [SD, 5.4] years) had baseline balanced steady-state free precession MR imaging before proton or photon radiation therapy. Associations among baseline supratentorial magnetization transfer ratio, radiation necrosis (spontaneously resolving/improving parenchymal enhancement within the radiation field)3, age, and the presence of visible brain metastases were explored by logistic regression and parametric/nonparametric techniques as appropriate. Twenty-three of 95 (24.2%) children (44% female; mean age, 10.7 [SD, 6.7] years) developed radiation necrosis after radiation therapy (19 infratentorial, 1 supratentorial, 3 both). The mean pretreatment supratentorial WM magnetization transfer ratio was significantly lower in these children (43.18 versus 43.50, P = .03). There was no association between the supratentorial WM magnetization transfer ratio and age, sex, risk/treatment stratum, or the presence of visible brain metastases. A lower baseline supratentorial WM magnetization transfer ratio may indicate underlying structural WM susceptibility to radiation necrosis and may identify children at risk for developing radiation necrosis after craniospinal irradiation for medulloblastoma.
Highlights
BACKGROUND AND PURPOSERadiation necrosis, for which abnormal WM enhancement is a hallmark, is an uncommon complication of craniospinal irradiation in children with medulloblastoma
The mean pretreatment supratentorial WM magnetization transfer ratio was significantly lower in these children (43.18 versus 43.50, P 1⁄4 .03)
Current pathologic studies of Radiation necrosis (RN) suggest that damage to vascular endothelial cells and myelin-producing oligodendrocytes leads to increased vascular permeability, gliosis, and demyelination.[4,5]
Summary
Ninety-five eligible patients with medulloblastoma (41% female; mean age, 11.0 [SD, 5.4] years) had baseline balanced steady-state free precession MR imaging before proton or photon radiation therapy. Associations among baseline supratentorial magnetization transfer ratio, radiation necrosis (spontaneously resolving/improving parenchymal enhancement within the radiation field)[3], age, and the presence of visible brain metastases were explored by logistic regression and parametric/nonparametric techniques as appropriate. This prospective study was performed with the approval of the St. Jude Children's Research Hospital IRB and informed parental or patient consent and/or assent. Patients were stratified into low-, standard-, and high-risk treatment groups on the basis of the molecular subgroup, postsurgical tumor volume, histology, MYC/MYCN, and metastatic status (M0 to M4) (Fig 1).[14,15] Treatment guidelines for risk-adapted photon or proton craniospinal and conformal primary (posterior fossa) site irradiation ranged from 15 to 51 Gy
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