title: Assessment of focal liver reaction by multiphasic CT after stereotactic single-dose radiotherapy of liver tumors.
abstract: OBJECTIVE
  To characterize and quantitatively assess focal radiation reactions in the liver after stereotactic single-dose radiotherapy for liver malignancies.
  
  
  METHODS
  A total of 131 multiphasic CT scans were performed in 36 patients before and after stereotactic radiotherapy for liver tumors. The examination protocol included a nonenhanced scan and contrast-enhanced scans at different times after contrast injection. The volume of the reaction was determined in each scan and the threshold dose calculated using the dose-volume histogram of the treatment plan.
  
  
  RESULTS
  Every patient showed a focal radiation reaction on at least one follow-up examination. In 74% of the posttherapeutic scans, a sharply demarcated hypodense area surrounded the treated tumor in the nonenhanced scans. The reaction occurred at a median of 1.8 months (range 1.2-4.6) after radiotherapy. The median threshold dose was 13.7 Gy (range 8.9-19.2). The threshold dose strongly correlated with the time of detection after therapy (r = 0.7). Radiologically, three reaction types were found on the enhanced scans: type 1, portal-venous phase: hypodense and late phase: isodense; type 2, portal-venous phase: hypodense and late phase: hyperdense; and type 3, portal-venous phase: isodense/hyperdense and late phase: hyperdense. Type 1 or 2 reactions were observed significantly earlier than type 3 (p <0.05). The median threshold dose for type 1 or 2 reactions was significantly lower than for type 3 (p <0.05). The reaction volume decreased with longer follow-up (2-4 months: median 40% of initial volume). The reaction types shifted with follow-up: 58% were of type 1 at the initial manifestation and 58% were of type 3 at the next examination thereafter.
  
  
  CONCLUSIONS
  A focal radiation reaction occurs after stereotactic single-dose therapy in the liver. The volume of the reaction decreases and changes its radiologic appearance during follow-up. This reaction has to be differentiated from recurrent tumor.
authors.affiliation: Division of Radiation Oncology, German Cancer Research Center, Heidelberg, Germany. k.herfarth@dkfz.de
authors.forename: Klaus K
authors.initials: KK
authors.lastname: Herfarth
authors.forename: Holger
authors.initials: H
authors.lastname: Hof
authors.forename: Malte L
authors.initials: ML
authors.lastname: Bahner
authors.forename: Frank
authors.initials: F
authors.lastname: Lohr
authors.forename: Angelika
authors.initials: A
authors.lastname: Höss
authors.forename: Gerhard
authors.initials: G
authors.lastname: van Kaick
authors.forename: Michael
authors.initials: M
authors.lastname: Wannenmacher
authors.forename: Jürgen
authors.initials: J
authors.lastname: Debus
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging / Q000528:radiation effects*; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D011879:Radiotherapy Dosage; D013238:Stereotaxic Techniques; D013997:Time Factors; D014057:Tomography, X-Ray Computed