Distinguishing post-treatment changes from recurrent disease in cholangiocarcinoma: a case report
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Three-dimensional techniques for radiotherapy have expanded possibilities for partial volume liver radiotherapy. Characteristic, transient radiographic changes can occur in the absence of clinical radiation-induced liver disease after hepatic radiotherapy and must be distinguished from local recurrence.
In this report, we describe computed tomography changes after chemoradiotherapy for cholangiocarcinoma as an example of collaboration to determine the clinical significance of the radiographic finding.
Because of improved three-dimensional, conformal radiotherapy techniques, consultation across disciplines may be necessary to interpret post-treatment imaging findings.
KeywordsCommon Bile Duct Cholangiocarcinoma Common Hepatic Duct Prescription Isodose Line Compute Tomography Change
Conformal radiotherapy (RT) techniques allow for the delivery of high radiation doses to fields encompassing partial liver volumes as a component of combined modality cancer treatment. RT doses are limited by concerns for radiation-induced liver disease (RILD) . Imaging changes may occur after treatment, in the absence of treatment-related toxicity, and must be distinguished from possible disease recurrence. In this report, we describe CT changes after chemoradiotherapy for cholangiocarcinoma as an example of the challenge of distinguishing treatment effect from disease recurrence.
Conformal RT techniques may produce imaging changes that must be distinguished from disease recurrence. Although RT to the entire liver is known to produce clinical hepatic toxicity at doses of 30 to 35 Gy in standard fractionation, three-dimensional conformal planning techniques allow delivery of higher radiation doses to partial liver target volumes [1, 2, 3]. Current methods closely appose regions of high and low dose by escalating dose to the treatment volume and minimizing exposure to adjacent normal hepatic parenchyma . Yamasaki et al. reviewed contrast-enhanced CT studies from 31 patients who received high-dose conformal radiation therapy to a partial liver volume and found minimal correlation between radiation-induced tomographic changes and clinical radiation hepatitis, which was observed in only 6% of subjects. 74% of patients studied displayed regions of low attenuation in treatment volume in post-treatment CT scans, but no scans showed linear margins . The absence of crisp margins of attenuation may be explained by the use of nonaxial, noncoplanar overlapping fields in the study, in contrast to the four-field coplanar plan presented in this case. Other CT changes after partial volume hepatic radiation range from linear regions of low density corresponding to parallel opposed portals [6, 7] to a peripheral, curved band of low attenuation in the upper liver after intensity-modulated radiation therapy for mesothelioma .
Imaging changes after chemoradiation of the liver are a separate entity distinct from RILD, a syndrome distinguished by the clinical triad of hepagatomegaly, ascites, and elevated liver enzymes, predominantly alkaline phosphatase. Although RILD may produce hepatic failure, most cases resolve within three months after radiation . The pathologic features of RILD include severe central venous congestion of hepatic lobules, relative sparing of larger veins, and endothelial damage in small veins [4, 9, 10]. Clinically, RILD is similar to Budd-Chiari syndrome, but with sparing of larger veins such as the vena cava. Although RILD occurs with conventional radiation techniques [1, 2, 3], RT fields encompassing the whole liver may be safely delivered if the mean liver dose remains below 30 to 37 Gy [4, 11, 12]. Multiple three-dimensional models exist to predict tolerance of the liver to higher doses of partial volume radiation .
Imaging changes after partial volume hepatic radiation are usually subclinical and do not predict RILD . In addition to CT changes involving the treated region after RT, other imaging findings include T1 hypointensity, T2 hyperintensity, and sustained contrast enhancement on MRI ; decreased echogenicity on ultrasound ; and decreased uptake of particulate reticuloendothelial contrast . Collectively, imaging changes after hepatic RT may display the effects of edema or vascular congestion, consistent with a proposed vascular etiology for radiation-induced liver damage.
Three-dimensional techniques for RT planning and delivery have expanded the possibilities for high-dose partial volume liver RT. Characteristic, transient radiographic changes occur in the absence of clinical RILD after hepatic RT and must be distinguished from recurrent disease on follow-up imaging studies. Because of the complexity of radiation treatment techniques, consultation across disciplines may be necessary to determine the significance of post-treatment imaging findings.
Written consent was obtained from the patient for publication of the report and accompanying imaging. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
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