Assessment of focal liver reaction by multiphasic CT after stereotactic single-dose radiotherapy of liver tumors

To characterize and quantitatively assess focal radiation reactions in the liver after stereotactic single-dose radiotherapy for liver malignancies. 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. 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