OBJECTIVETo review the appearance of radiation-induced liver injury on computer tomography for quantitative assessment of dosimetric changes in different radiological reactions and the influence of time-effect.

METHODSThe focal liver reactions of 35 patients treated with three-dimensional conformal radiation therapy (3-D CRT) for liver malignancies were evaluated, with the applied doses of 36-65 Gy in 4-28 fractions completed in 8-41 days. All patients received nonenhanced CT scan and arterial-dominant phase contrast-enhanced CT scan 1-6 months after therapy. The liver tissue density in irradiated and nonirradiated liver was compared, and the reaction type and the threshold dose determined radiologically.

RESULTSOn at least one follow-up examination, 51.4% of patients were found to have a focal radiation reaction in the liver. The radiation reaction was hypodense in 43.75% of the follow-up nonenhanced CT examinations and in 19.23% of arterial-dominant phase contrast-enhanced CT scans. It was hyperdense in 42.31% of arterial-dominant phase contrast-enhanced CT scans. The median threshold dose inducing a radiation reaction was 30.8 Gy (range 18-42.8 Gy). The detected threshold dose was positively correlated with the time of detection of the reaction (P=0.041), with a correlation coefficient of -0.473. On arterial-dominant phase contrast-enhanced CT scans, the threshold dose was significantly higher for hyperdense than for hypodense changes (P=0.017). In additional follow-up, the reaction volume decreased and the reaction types changed on arterial-dominant phase contrast-enhanced CT scans.

CONCLUSIONSThe threshold dose can be different in different radiological reaction types on multiphase CT scans. The detected threshold dose is inversely correlated with the time of detection of the early reaction. Multiphase contrast-enhanced CT is helpful to distinguish radiation reactions from recurrent tumors.