title: Differentiation between intra-axial metastatic tumor progression and radiation injury following fractionated radiation therapy or stereotactic radiosurgery using MR spectroscopy, perfusion MR imaging or volume progression modeling.
abstract: OBJECTIVE
  To determine the accuracy of magnetic resonance spectroscopy (MRS), perfusion MR imaging (MRP), or volume modeling in distinguishing tumor progression from radiation injury following radiotherapy for brain metastasis.
  
  
  METHODS
  Twenty-six patients with 33 intra-axial metastatic lesions who underwent MRS (n=41) with or without MRP (n=32) after cranial irradiation were retrospectively studied. The final diagnosis was based on histopathology (n=4) or magnetic resonance imaging (MRI) follow-up with clinical correlation (n=29). Cho/Cr (choline/creatinine), Cho/NAA (choline/N-acetylaspartate), Cho/nCho (choline/contralateral normal brain choline) ratios were retrospectively calculated for the multi-voxel MRS. Relative cerebral blood volume (rCBV), relative peak height (rPH) and percentage of signal-intensity recovery (PSR) were also retrospectively derived for the MRPs. Tumor volumes were determined using manual segmentation method and analyzed using different volume progression modeling. Different ratios or models were tested and plotted on the receiver operating characteristic curve (ROC), with their performances quantified as area under the ROC curve (AUC). MRI follow-up time was calculated from the date of initial radiotherapy until the last MRI or the last MRI before surgical diagnosis.
  
  
  RESULTS
  Median MRI follow-up was 16 months (range: 2-33). Thirty percent of lesions (n=10) were determined to be radiation injury; 70% (n=23) were determined to be tumor progression. For the MRS, Cho/nCho had the best performance (AUC of 0.612), and Cho/nCho >1.2 had 33% sensitivity and 100% specificity in predicting tumor progression. For the MRP, rCBV had the best performance (AUC of 0.802), and rCBV >2 had 56% sensitivity and 100% specificity. The best volume model was percent increase (AUC of 0.891); 65% tumor volume increase had 100% sensitivity and 80% specificity.
  
  
  CONCLUSIONS
  Cho/nCho of MRS, rCBV of MRP, and percent increase of MRI volume modeling provide the best discrimination of intra-axial metastatic tumor progression from radiation injury for their respective modalities. Cho/nCho and rCBV appear to have high specificities but low sensitivities. In contrast, percent volume increase of 65% can be a highly sensitive and moderately specific predictor for tumor progression after radiotherapy. Future incorporation of 65% volume increase as a pretest selection criterion may compensate for the low sensitivities of MRS and MRP.
authors.affiliation: Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI 48073, USA.
authors.forename: Jiayi
authors.initials: J
authors.lastname: Huang
authors.forename: Ay-Ming
authors.initials: AM
authors.lastname: Wang
authors.forename: Anil
authors.initials: A
authors.lastname: Shetty
authors.forename: Ann H
authors.initials: AH
authors.lastname: Maitz
authors.forename: Di
authors.initials: D
authors.lastname: Yan
authors.forename: Danielle
authors.initials: D
authors.lastname: Doyle
authors.forename: Kenneth
authors.initials: K
authors.lastname: Richey
authors.forename: Sean
authors.initials: S
authors.lastname: Park
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Pieper
authors.forename: Peter Y
authors.initials: PY
authors.lastname: Chen
authors.forename: Inga Siiner
authors.initials: IS
authors.lastname: Grills
mesh_terms: D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D003937:Diagnosis, Differential; D018450:Disease Progression; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis / Q000175:diagnosis*; D010477:Perfusion; D012372:ROC Curve; D011832:Radiation Injuries / Q000175:diagnosis* / Q000473:pathology; D016634:Radiosurgery / Q000379:methods*