High-dose localized radiation therapy for treatment of hepatic malignant tumors: CT findings and their relation to radiation hepatitis.

OBJECTIVE High-dose radiation therapy of the liver performed using overlapping portals defined by a three-dimensional treatment-planning system (conformal radiation therapy) is a new method of treating hepatic tumors. This study was performed to delineate the differences in the CT appearances of the liver after therapy compared with other methods of radiotherapy and to correlate imaging findings to clinical findings of radiation hepatitis. MATERIALS AND METHODS Contrast-enhanced CT scans were obtained at 8- to 12-week intervals on 31 consecutive patients with primary or metastatic hepatic malignant tumors. All had undergone high-dose conformal radiation therapy and injection of fluorodeoxyuridine into the hepatic artery as part of the treatment for unresectable hepatic neoplasms. Tumor size, location, presence of changes within the target volume after therapy, presence of atrophy of the treated segments or hypertrophy of the untreated segments, ascites, and any changes in adjacent organs seen on serial CT scans obtained before and after treatment were recorded. Clinical records were reviewed for evidence of radiation hepatitis (nonmalignant ascites evident on physical examination and a twofold elevation of alkaline phosphatase in the anicteric patient). RESULTS In 23 (74%) of the 31 patients, follow-up CT studies after treatment showed a low-attenuation area adjacent to the hepatic tumor in the target volume. In two patients with fatty infiltration of the liver, CT showed relative increased density in the treatment portal. A sharp, straight interface was rarely seen at the treatment margin. Maximal effect was seen 2-3 months after completion of therapy and persisted for up to 3 months. Atrophy in the treated segment or lobe was seen in four patients, hypertrophy of the untreated liver was seen in four patients, and both effects were seen in seven patients. Extrahepatic effects included segmental right renal atrophy in three patients and duodenal wall thickening in two patients. Only two patients (6%) in this series had clinical evidence of radiation hepatitis. CONCLUSION High-dose localized radiotherapy of the liver results in reversible hypodense regions in the liver parenchyma within the target volume that do not have a sharp interface delineating the radiation portal. This appearance should not be confused with tumor progression or irreversible liver injury. The changes evident on CT scans after therapy are not predictive of radiation hepatitis.