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

Abstract

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