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Original Research |
1 All authors: Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins Hospital, 601 N Caroline St., Rm. 100, Baltimore, MD 21287.
Received May 11, 2007;
accepted after revision July 23, 2007.
Address correspondence to I. R. Kamel
(ikamel{at}jhmi.edu).
Abstract
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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MATERIALS AND METHODS. Sixty-six targeted lesions in 26 patients (18 men, eight women; mean age, 57 years) with hepatic metastasis of neuroendocrine tumors treated with TACE were retrospectively analyzed. MRI studies were performed before and after TACE. Imaging features included tumor size, percentage of enhancement in the arterial and portal venous phases, and diffusion-weighted imaging apparent diffusion coefficients (ADCs) of the tumor, liver, and spleen. Tumor response to treatment was recorded according to World Health Organization criteria and Response Evaluation Criteria in Solid Tumors. Liver function tests were performed, and clinical performance was assessed before and after treatment. Statistical analysis included paired Student's t tests and Kaplan-Meier survival curves.
RESULTS. Mean tumor size and percentage enhancement in the arterial and portal venous phases decreased significantly after treatment (p < 0.0001). The tumor ADC increased from 1.51 x 10-3 mm2/s before treatment to 1.79 x 10-3 mm2/s after treatment (p < 0.0001), but the ADCs for the liver and spleen remained unchanged. Despite the change in tumor size, no patient in this cohort achieved complete response according to World Health Organization criteria and Response Evaluation Criteria in Solid Tumors. Partial response was achieved in only 27% and 23% of the patients according to the respective criteria. Results of liver function tests and performance status also remained unchanged. The mean survival period for all patients was 78 months.
CONCLUSION. Contrast-enhanced and diffusion-weighted imaging showed significant changes after TACE of neuroendocrine tumors and can be used to assess response of targeted tumors.
Keywords: diffusion-weighted MRI • dynamic contrast-enhanced MRI • liver • transcatheter arterial chemoembolization
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Response assessment in solid tumors is established with imaging for measurement of tumor size according to the modified World Health Organization (WHO) or the Response Evaluation Criteria in Solid Tumors (RECIST) guidelines [12, 13]. TACE has been shown to decrease tumor size, but despite favorable clinical outcome, many responses do not qualify as complete according to the WHO and RECIST guidelines [14]. Moreover, a cystlike appearance of lesions after TACE, indicating response to treatment without alteration in size, is possible [15]. Therefore, a decrease in functional tumor burden with TACE cannot be fully assessed with the current WHO and RECIST guidelines, which rely solely on anatomic changes. Functional contrast-enhanced and diffusion-weighted MRI (DWI) has been introduced as a new technique for assessing tumor response after TACE in patients with primary liver cancer [14, 16]. This approach has been shown to help identify intracellular changes in tumor necrosis in patients with hepatocellular carcinoma treated with TACE and has led the way to the acquisition of important information about tumor burden and function. To our knowledge, this approach has not been used to assess the response of NET metastasis to TACE.
In this study, our aim was to evaluate multiparametric MRI anatomic and functional changes in NET hepatic metastatic lesions after sequential treatments with TACE. For the standard of reference, response evaluation was recorded according to the WHO and RECIST guidelines. In addition, overall imaging response was supported by results of liver function tests, patient performance status, and results of analysis of survival data.
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The location of the primary tumors in patients who had a histologic diagnosis of carcinoid included the small bowel in three patients, the large bowel in six patients, the stomach and duodenum in three patients, and other locations in two patients. Patients who had undergone chemotherapy or surgery were not excluded from the study. Targeted lesions close to the diaphragm were excluded because of breathing artifacts. Targeted lesions smaller than 1 cm also were excluded from the study because they were too small to be detected with DWI.
Chemoembolization Technique
According to our standard institutional protocol, experienced
interventional radiologists performed all TACE procedures. For most patients
with bilateral liver disease, only one lobe of the liver was subjected to
embolization during each treatment session. To prevent carcinoid crisis,
somatostatin analogues were preoperatively administered to patients with
active hormone hypersecretion. Chemoembolization was performed as previously
described [14]. Selective
catheterization of the feeding artery was followed by infusion of a solution
containing 100 mg of cisplatin, 50 mg of doxorubicin (Adriamycin, Pharmacia
& Upjohn), and 10 mg of mitomycin C in a 1:1-2:1 mixture of iodized oil
(Lipiodol, Guerbet). The infusion was followed by injection of either 150- to
250-µm polyvinyl alcohol particles (Ivalon, Interventional Therapeutic) or
300- to 500-µm trisacryl gelatin microspheres (Embospheres, Biosphere
Medical) to slow arterial inflow and prevent washout of the chemotherapeutic
agent.
CT Technique
Within 24 hours after TACE, all patients underwent unenhanced MDCT with a
Volume Zoom scanner (Somatom Plus 4, Siemens Medical Solutions). Scanning
parameters were 120 kVp, 210 mA, 5-mm section collimation, and 5-mm image
reconstruction. Technical success of the procedure was shown by the presence
of intratumoral iodized oil deposition and relative sparing of the nontumorous
liver parenchyma.
MRI Technique and Imaging Features
All patients underwent baseline and follow-up MRI with a 1.5-T unit (CV/i,
GE Healthcare) and a phased-array torso coil. The imaging protocol included
T2-weighted fast spin-echo images (matrix size, 256 x 256; slice
thickness, 8 mm; interslice gap, 2 mm; TR/TE, 5,000/100; receiver bandwidth,
32 kHz), breath-hold diffusion-weighted echo-planar images (5,000-6,500/110;
matrix size, 128 x 128; slice thickness, 8 mm; interslice gap, 2 mm; b
value, 500; receiver bandwidth, 64 kHz), and breath-hold unenhanced and
contrast-enhanced (0.1 mmol/kg IV of gadodiamide, [Omniscan, GE Healthcare])
T1-weighted 3D fat-suppressed spoiled gradient-echo images (5.1/1.2; field of
view, 320-400 mm2; matrix size, 192 x 160; slice thickness,
4-6 mm; receiver bandwidth, 64 kHz; flip angle, 15°) in the arterial (20
seconds after contrast administration) and portal venous (60 seconds after
contrast administration) phases.
We compared imaging features on unenhanced MRI and post-TACE MRI. The features included tumor size, percentage of arterial and portal venous targeted tumor enhancement, patency of the portal vein, and ADCs of tumors, liver, and spleen. Images for each patient were obtained retrospectively with a workstation (Advantage Windows, GE Healthcare) and were interpreted by consensus of two experienced MRI radiologists in the same reading session to ensure careful comparison of preprocedural and postprocedural MRI features. Image magnification and window and level settings were adjusted accordingly, and the relevant settings were recorded. Bidimensional targeted tumor measurements (maximal tumor diameter and largest perpendicular diameter), percentage of arterial and portal venous targeted tumor enhancement, and patency of the portal vein were recorded. For patients who underwent more than one TACE session, the MRI study performed after the last session was used for comparison. Percentage of enhancement was visually estimated as enhancement seen on the axial image with the largest tumor diameter and was quantified as follows: less than 25%, 25% to less than 50%, 50-75%, and greater than 75%. ADC maps were generated from the diffusion-weighted images, and values were recorded by placement of a region of interest over the entire treated mass, as seen on the image with the largest lesion size. Percentage of iodized oil deposition on CT was estimated with the same four quartiles used for percentage of tumor enhancement. For patients who had undergone multiple treatments, the cumulative iodized oil deposition in the targeted lesion was recorded.
Anatomic tumor response was recorded and classified according to the WHO and RECIST guidelines as complete response, partial response, stable disease, or progressive disease. Complete response was described as tumor disappearance confirmed 4 weeks after treatment. Partial response was defined as corresponding to a 50% decrease in the summation of the products of bidimensional measurements of tumor lesions according to the WHO criteria and to at least a 30% decrease in the sum of the longest diameter of targeted lesions according to the RECIST. Stable disease was defined as neither sufficient shrinkage to qualify for partial response nor sufficient increase to qualify for progressive disease. Progressive disease was defined as at least a 20% increase in the sum of the longest diameter of target lesions according to the RECIST or an at least 25% increase in the summation of the products of bidimensional measurements of tumor lesions according to the WHO guidelines [12, 13]. Tumor response determined as change in tumor size according to the WHO and RECIST guidelines was recorded.
Clinical Data
Laboratory data included results of liver function tests before and after
treatment. Hormonal and tumor markers were not included in the analysis
because they were primarily used for diagnostic purposes. The clinical status
of each patient was assessed before and after treatment according to the
Eastern Cooperative Oncology Group performance status scale
[17].
Survival Data
Survival rates were calculated from the date of diagnosis of metastatic
disease because in some cases there was no available information on the time
of diagnosis of the primary lesion.
Statistical Analysis
Statistical analysis was performed with the SPSS 14.0 statistical software
package (SPSS). Paired Student's t tests and Wilcoxon's rank tests
were used for comparisons of pretreatment and posttreatment values. Tumor
size, enhancement, and ADC in patients with pancreatic NETs were compared with
those in patients with nonpancreatic NETs. The same variables were compared
for patients with first-line and those with second-line TACE therapy. Survival
rates were calculated on the basis of the time of diagnosis of metastatic
liver disease and analyzed with the Kaplan-Meier method. A value of p
< 0.05 was considered statistically significant.
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Imaging Data
The mean time between pretreatment and posttreatment MRI was 206 ±
201 (SD) days. The mean longest tumor diameter was 5.6 ± 3.1 cm before
treatment and 4.6 ± 3.1 cm after treatment (p < 0.0001), as
shown in Table 2. Mean tumor
enhancement in the arterial phase was 60.8% ± 25.3% before treatment
and 31.1% ± 30.8% after treatment (p < 0.0001). Mean tumor
portal venous enhancement was 82.4% ± 20.7% before and 42.5% ±
36.1% after treatment (p < 0.0001) (Fig.
1A,
1B,
1C,
1D,
1E,
1F,
1G). Mean tumor ADC increased
from 1.51 ± 0.55 x 10-3 mm2/s before
treatment to 1.79 ± 0.54 x 10-3 mm2/s after
treatment (p < 0.0001). The ADCs for liver (p = 0.17) and
spleen (p = 0.58) remained unchanged before and after treatment. A
mean change of 26.4% ± 45.5% in tumor ADC was recorded for all targeted
lesions. According to the WHO criteria, seven (27%) patients had a partial
response, and the other 19 (73%) had stable disease. A mean change of 34.5%
± 22.9% in bidimensional tumor size was found for all patients.
According to the RECIST, six (23%) of the patients had a partial response, 19
(73%) had stable disease, and one (4%) had progressive disease. A mean change
of 16.3% ± 27.2% in unidimensional tumor size according to the RECIST
was recorded. Tested correlation between the WHO and RECIST guidelines was
significant (p < 0.001, 
= 0.8). No significant correlation,
however, was detected between the WHO criteria and mean tumor ADC (p
= 0.8, = 0.025) or the RECIST and mean tumor ADC (p = 0.2,
= 0.2) (Table 3).
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Testing for possible correlation between tumor ADC after treatment,
percentage of arterial and portal venous tumor enhancement after treatment,
and percentage of iodized oil deposition for each targeted lesion showed no
correlation between percentage of iodized oil deposition and tumor ADC after
treatment (p = 0.3, = 0.13) or between percentage of iodized
oil deposition and percentage of tumor enhancement after treatment (p
= 0.5, = 0.09). A marginal value of p = 0.06 ( = 0.24) was
observed in the test of correlation between percentage of tumor enhancement in
the portal venous phase and iodized oil deposition. The tumor variables size,
enhancement, and ADC in patients with pancreatic NETs were not significantly
different from those in patients with nonpancreatic NETs. Similarly, the tumor
variables in patients undergoing TACE as first-line treatment were not
significantly different from those in patients undergoing TACE as a
second-line treatment.
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Survival Data
The mean survival period for all patients was 78 months
(Fig. 2). There was no
statistically significant difference between the survival rate of patients
with metastatic carcinoid and that of patients with islet cell lesions
(logrank p = 0.65). Moreover, there was no statistically significant
difference between the survival rate of patients who underwent TACE as
first-line treatment and that of those who underwent the procedure as
second-line treatment (log-rank p = 0.87).
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Assessment of response to treatment is necessary for clinical management and is critical for the evaluation of clinical trials. Currently used tumor response criteria include the WHO and RECIST guidelines [12, 13]. Both sets of guidelines rely on anatomic information on tumor status derived before and after treatment, measured as a change in tumor size. However, the validity of the criteria has been challenged with various types of tumors and treatments, mainly because of a need for additional information on functional tumor burden [23]. New targeted cancer therapies may not result in changes in tumor size that qualify as complete or partial response. They may, however, lead to cellular necrosis, measured with functional imaging (PET, SPECT, and MRI). As a form of targeted therapy, TACE has been effective in reducing tumor burden in patients with NET hepatic metastasis, but despite the favorable clinical outcome, response to treatment often does not meet the criteria for complete response.
The need for functional assessment of tumor burden in NET hepatic metastasis was introduced in a study of treated NET metastases assessed with 111In-pentetreotide SPECT [24]. Not all tumors, however, exhibit uptake with this imaging technique. DWI is a functional technique based on motion of water molecules across cell membranes. DWI has been used to evaluate tumor cell death of primary unresectable hepatocellular carcinomas treated with TACE [14, 16]. Viable highly cellular tumors have intact cell membranes that restrict the motion of water molecules, producing a low ADC. After TACE, cellular necrosis causes membrane disruption and increases membranous permeability, allowing free diffusion of water molecules and an increase in ADC [14, 16]. Our results show that DWI can be used to assess response to treatment on a functional molecular level and to quantify tumor cell death by showing the state of water diffusion across tumor cell membranes on ADC maps. This observation may explain the lack of correlation between the WHO and RECIST guidelines and the DWI measurements. The first two refer to anatomic information, and the last offers information on a cellular level.
Another indicator of treatment effectiveness measured in our study is tumor vascularity, shown by percentage of enhancement of targeted lesions in the arterial and portal venous phases of imaging before and after treatment. Several studies have shown a decrease in tumor vascularity after successful treatment with TACE. It is difficult, however, to compare results of previous reports because of variability in the measurement methods of tumor vascularity [25]. Contrast-enhanced perfusion imaging is a promising method of measuring tumor vascularity in a more reproducible manner [26, 27].
Our results showed lack of correlation between iodized oil deposition, tumor DWI measurements, and arterial and portal venous enhancement measurements. This lack of correlation may be due to the different physical properties measured. Contrast enhancement is determined by the amount of contrast material in the extracellular space, DWI is a measure of water motion across membranes, and iodized oil deposition refers to a possible biochemical tumor cell pump defect [28]. Iodized oil deposition has been shown not to correlate well with tissue necrosis [29]. In our experience, the main use of unenhanced CT has been to determine the technical success of TACE by verifying adequate tumor targeting. Moreover, iodized oil deposition and arterial and portal venous tumor enhancement are based on visual estimates, whereas ADC is a computed value and can be objectively reproduced.
Patients with untreated hepatic metastasis historically have a 5-year survival rate of 35% with a median survival period of 2-4 years [30, 31]. Comparison of survival data with findings in other studies shows that our mean survival period of 78 months is in accordance with other reported survival times [8, 11]. Eriksson et al. [10] reported a median survival period of 80 months in a group of 41 patients with NET metastasis, but all of those patients had previously undergone other medical treatments. Other reports [8, 21, 32] have suggested that the natural history of metastatic NETs is unpredictable and that the median survival period among these patients after embolization treatment ranges from 13 to 80 months.
Our study had several limitations. Because of the rarity of the disorder, the number of subjects was small. Therefore, we were not able to detect trends between the carcinoid and the neuroendocrine groups or between the first-line TACE and second-line TACE groups. Future studies with a larger subset of patients are warranted to assess the correlation between tumor enhancement and ADC with an objective outcome, such as survival. Moreover, patients who had incomplete imaging evaluations or had tumors less than 1 cm in diameter were excluded, leading to potential selection bias. NET hepatic metastasis is known for a long, variable, and indolent course, making it difficult to assess survival benefit. Histopathologic data were not obtained for any of the patients in the study. Therefore, tumor cell death was measured only with DWI. Previous reports [14, 16], however, have shown good correlation between the histopathologic percentage of necrosis and the ADC obtained with DWI.
The results of our analysis suggest that multiparametric DWI may effectively show treatment effect after TACE in patients with hepatic metastasis of NETs. The addition of DWI seems to provide important information about the functional tumor burden, whereas contrast-enhanced MRI depicts morphologic changes in NET hepatic metastasis after TACE. These preliminary results need to be further validated in a prospective randomized way that may strengthen the role of multiparametric functional MRI.
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