Essay: Patients and methods

Study design and data acquisition
From October 2013 through October 2015, 50 patients with histopathologically –proven colorectal cancer were referred to perform post therapeutic follow up PET/CT. The study took place in a private center and Egyptian military hospital. The prospective study protocol was approved by the ethical committee.
All clinical and histo-pathological information were collected from the patient’s files. This included the TNM classification and localization of the primary tumor, tumer marker levels, the type of treatment received and current reason for FDG-PET/CT referral.
PATIENTS:
We evaluated PET/CT and enhanced CT scans for patients who underwent colorectal cancer surgery followed by chemo and radiotherapy. No age predilection and both sexes were included.
Exclusion criteria :
Patients with the following conditions were excluded from the study:
• Strong history of atopic disorders.
• Serum creatinine level above 2mg/dl .
• Recent surgery less than 6 weeks .
• Radiotherapy within less than 3 months.
• Chemotherapy within less than 3 weeks.
METHODS:
PET/CT and enhanced CT study were performed for each patient as follows:
Procedures of Whole-Body PET/CT Imaging with 18F-FDG:-
PET/CT was performed on an integrated scanner (Philips 128 slice CT) that combines both CT and PET capabilities in two sequential gantries, avoiding the need for patient motion between the CT and PET components of the study giving accurate co-registration of the CT and PET data.
• Patients fasted for at least 6 hours before the examination, except for water and glucose free fluid.
• Blood glucose levels measured less than 200 mg/dL.
• Patient’s weight was measured.
• A dose of (0.18–0.21mCi/kg, 5-14 mCi) FDG was injected intravenously. The patients rested in a quiet room. After the 45–60-minute uptake period, the patients were asked to void just before entering the examination room.
• No oral or intravenous contrast agent was used for the PET-CT examination.
• Multi-detector CT examination from the base of the skull to the upper thighs (120 mA, 140 kVp, table speed = 13.5 mm per rotation and thickness of 4 mm) was planned.
• After CT acquisition, PET acquisition of the same axial range started with the patient in the same position on the table for 2–3 minutes per bed position.
• PET data was acquired by using a matrix of 128×128 pixels. CT-based attenuation correction of the emission images was used.
• After PET data acquisition was completed, the reconstructed attenuation corrected PET images, CT images, and fused images of matching pairs of PET and CT images were available for review in axial, coronal, and sagittal planes, as well as in maximum intensity projections and in three-dimensional cine mode.
• Contrast enhanced CT was performed by the same scanner 20-50 seconds after giving bolus injection of non-ionic iodinated contrast at dose about 2-3 ml/KG of body weight. Scanning were acquired from the base of the skull till the mid-thigh may involve the whole body in case of extensive skeletal deposits ,using 2.5 mm thickness section .
Interpretation and image analysis:
– Images were interpreted by experienced nuclear medicine physicians and radiologist.
– Qualitative assessment for presence of hyper-metabolic lesions was evaluated on corrected PET images.
– Semi-quantitative evaluation was performed using the Standardized Uptake Value (SUVmax) according to the following formula: SUVmax = maximum measured activity in the volume of interest (millicuries per milliliter)/injected dose of FDG (millicuries) per gram of body weight of all abnormal foci
The standard SUVmax of 2.5 was considered a cutoff point, where lesions with SUVmax of 2.5 and above in PET/CT studies were considered positive for disease involvement while findings with SUVmax below 2.5 were considered to be insignificant of disease involvement .
– Contrast enhanced CT images were evaluated for the presence of hepatic focal lesions,lymph node size(more than 10mm in its short axis) ,lymph node morphology , pulmonary nodules ,peritoneal masses ,operative bed masses and skeletal lesions .
– Comparison with other clinical and diagnostic methods including laboratory tests (tumor markers) and other pathological findings was performed .
Comparison between PET-CT results and enhanced CT results and were tabulated and statistically analyzed.
Statistical methods:
IBM SPSS statistics (V. 23.0, IBM Corp., USA, 2015) was used for data analysis.
Data were expressed as both percentage and number for categorized results.
Diagnostic validity test was used: It includes agreement and disagreement between 2 studied techniques.
Chi-square test to study the association between each 2 variables or defined as comparison between 2 independent groups as regards the categorized data.
The probability of error equal 0.05 was considered significant; while value at 0.01 and 0.001 are highly significant.
a. The diagnostic sensitivity: It is defined as the percentage of diseased cases, that truly diagnosed (TP) among total diseased cases (TP+FN).
b. The diagnostic specificity: It is defined as the percentage of non-diseased cases, that truly excluded by the test (TN) within total non-diseased cases (TN+FP).
c. The predictive value for a +ve test: It is defined as the percentage of cases truly diagnosed within total positive cases.
d. The predictive value for a -ve test: It is defined as the percentage of cases truly negative within total negative cases.
e. The efficacy or the diagnostic accuracy of the test: It is defined as the percentage of cases truly diseased plus truly non-diseased among total cases.
RESULTS
&
ILLUSTRATIVE
CASES
RESULTS
Fifty patients with histopathologically proven colorectal primary malignancy were evaluated for suspected local recurrence and metastasis using PET/CT and enhanced CT. Patient characteristics and demographic data are shown in table (1).
Table (1): Patient characteristics
Total number of patients 50
Male patients 25
Female patients 25
Mean age for males (age range from 40-76) years 59.9
Mean age for females (age range 26-76) years 56.8
Thirty-five out of fifty patients (70%) proved to have metastasis or local recurrent disease and the remaining fifteen patients were totally free.
Ninety-one diseased regions were detected in thirty-five patients, either local recurrence or distant metastases with distribution as shown in table (2).
Table (2): Regions of local recurrences or metastases proved by reference modalities
Region Number of patients
Local recurrence 19
Hepatic deposits 26
Pulmonary metastasis 14
Peritoneal deposits 8
Metastatic lymph nodes 20
Osseous deposits 3
Supra renal metastasis 1
On region based analysis, recurrent or metastatic lesions were detected as loco-regional, hepatic, pulmonary, peritoneal, supra renal, lymph nodes, and bone metastases. 18F-FDG PET/CT was superior to enhanced CT in detection of local recurrence in all 19 local recurrent lesions (100%) compared to only 14 out of 19 lesions (73.6%) detected by enhanced CT.
Twenty six hepatic deposits proved to be positive. PET/CT accurately detected 24 lesions (92.3%) and enhanced CT detected 20 lesions (76.9%). PET-CT was able to detect additional 4 hepatic deposits, not detected by CT, while enhanced CT detected two lesions that were missed by PET-CT.
Positive lesions were detected in 20 LN regions. PET/CT detected twenty (100%), while the enhanced CT detected six (30%). All missed LN lesions by enhanced CT were detected by PET/CT.
Fourteen pulmonary nodules proved to be metastatic. PET/CT accurately detected 12 lesions (85.7%) and enhanced CT detected 11 lesions (78.8%). PET-CT was able to detect one additional pulmonary metastasis, not detected by CT, while enhanced CT detected two lesions that were missed by PET-CT.
PET/CT accurately detected other lesions including (8 peritoneal, 1 suprarenal, and 3 osseous bone deposits). Enhanced CT detected eight lesions only (5 peritoneal, 1 suprarenal, and 2 osseous bone deposits) as shown in table (3).
Table (3): Regions of local recurrences or metastases as detected by PET/CT and Enhanced CT
Site of recurrence Diseased regions detected by reference modalities PET/CT Enhanced CT
Local 19 19(100%) 14(73.66%)
Liver 26 24(92.3%) 20(76.9%)
Lymph nodes 20 20(100%) 6 (30%)
Pulmonary nodules 14 12(85.7%) 11(78.8%)
Peritoneal deposits 8 8(100%) 5(62.5%)
Osseous deposits 3 3(100%) 2(66.6%)
Supra renal deposits 1 1(100%) 1(100%)
Total 91 87(95.7%) 57(62.6%)
In assessment of about 50 patients we suspected about 126 lesions .The agreement between the results of both PET- CT and reference modalities was about 94.4 % and p value = 0.000 which is highly significant . PET-CT agreed with reference modalities in 119 lesions as it was true positive in detection of 87 lesions and true negative in detection of 32 lesions, yet PET-CT disagreed with reference modalities in 7 lesions (5.3%) as it was false negative in 4 regions (two hepatic and two lung )and false positive in 3 operative bed recurrence regions as shown in table (4) and figure (35) .
Table (4): Agreement of PET-CT with the reference modalities in detection of post therapeutic colon cancer recurrence and metastasis (lesion based analysis n=126 )
Crosstab
Ref. Total
Negative positive
PET-CT
Result Negative Number of Patients 32 4 36
% 91.4% 4.4% 28.6%
Positive Number of Patients 3 87 90
% 8.6% 95.6% 71.4%
Total Number of Patients 35 91 126
% 100.0% 100.0% 100.0%
Fig. 35: chart showing the percentage of true positive (Sensitivity) and true negative (Specificity) of PET- CT in relation to the reference modalities in the detection of post therapeutic cancer colon recurrence and metastasis .
In assessment of about 50 patients we detectd about 126 lesions , the agreement between the results of both enahnced CT and reference modalities were about 58.7 % and p value = 0.51 which is insignificant .Enhanced CT agreed with reference modalities in 74 lesions as it was true positive in detection of 57 lesions and true negative in 17 lesions yet enhanced CT disagreed with reference modalities in 52 lesions about (41.3%) as it was false negative in 34 lesions and false postive in 18 lesions as shown in table (5) and figure (36).
Table (5): Agreement of CECT with the reference modalities in detection of post therapeutic colon cancer recurrence and metastasis (lesion based analysis n =126 )
Crosstab
Ref. Total
Negative Positive
CECT result Negative Number of Patients 17 34 51
% 48.6% 37.4% 40.5%
Positive Number of Patients 18 57 75
% 51.4% 62.6% 59.5%
Total Number of Patients 35 91 126
% 100.0% 100.0% 100.0%
Fig.36: Chart showing the percentage of true positive(Sensitivity) and true negative (Specificity) of CECT in relation to the reference modalities in detection of post therapeutic cancer colon recurrence and metastasis.
Table (6) compares the diagnostic performance of PET/CT and enhanced CT in detection of post theraputic cancer colon local recurrence and distant metastasis with higher sensitivity ,specificty ,postive predictive value ,negative predictive value and diagnostic efficacy for PET/CT as compred to enhanced CT .
Table (6): Diagnostic performance of PET/CT in comparison with CECT by regional lesions based analysis.
Sensitivity Specificity Positive predictive value Negative predictive value Diagnostic efficacy
PET – CT 95.6% 91.4% 96.7% 88.9% 94.4%
Enhanced CT 62.6% 48.6% 76.0% 33.3% 58%
ILLUSTRATIVE CASES
CASE NO. (1)
History:
A 57 years old female patient who underwent rectal resection for pathologically proven adenocarcinoma, followed by chemotherapy, presented 4 months later by left loin pain and elevated tumor markers. Enhanced CT revealed local operative bed mass encasing the left ureter with mild backpressure changes and enlarged left iliac LNs.
The patient received chemotherapy after 4 weeks the tumor markers started to decline. Assessment with PET-CT and CECT was done. The findings of the two modalities were compared.
CECT:
Fig.37: Axial post contrast CT image showing operative bed faintly enhancing mass (arrow) encasing the distal left ureter.
PET-CT:
Fig.38: Axial fused PET –CT image showing no metabolically active lesions noted in the operative bed.
CECT :
Fig.39: axial post contrast CT image showing left iliac enlarged LNs (arrow).
PET-CT:
Fig. 40: axial fused PET-CT image showing left iliac metabolically active LNs (arrow).
Conclusion:
Post-therapeutic PET-CT helped in the detection of abnormally increased activity in iliac lymph nodes while CECT depends on the size criteria that showed stationary size. PET-CT revealed no metabolically active lesion at the operative bed granulation tissue. These findings showed that PET-CT is more sensitive than CECT for post-therapeutic response evaluation.
CASE NO. (2)
History:
A 70 years old female patient who underwent colonic mass surgical resection for pathologically proven adenocarcinoma, presented 4 months later by elevated tumor markers. PET-CT revealed right upper lobe solitary pulmonary nodule for which underwent radiofrequency ablation was performed.
Immediate Post ablation PET-CT and CECT was done. The findings of the two studies were compared.
CECT:
Fig.41: axial CT image in lung window showing right upper lobe pulmonary nodule before radiofrequency ablation (arrow).
Fig.42: axial CT image in lung window showing right upper lobe pulmonary nodule immediately after radiofrequency ablation (arrow).
PET-CT :
Fig.43: axial PET attenuated corrected image and axial fused PET–CT image before radiofrequency ablation of right upper lobe metabolically active nodule (arrows).
Fig.44: axial PET attenuated corrected image and axial fused PET –CT image immediately after radiofrequency ablation of right upper lobe metabolically active nodule leaving a photopenic area (arrows).
CECT:
Fig.45: axial post contrast CT image showing left hepatic lobe focal lesion with faint peripheral enhancement (arrow).
PET –CT :
Fig.46: Axial PET-CT fused image showing left hepatic lobe metabolically active focal lesion (arrow).
Conclusion:
Metastatic pulmonary nodule and hepatic focal lesion were detected by both PET-CT and contrast-enhanced CT. Post radiofrequency ablation assessment for the pulmonary nodule by contrast-enhanced CT showed stationary size depending on the size criteria (appreciable change in size needs time), while PET-CT revealed a photopenic area corresponding to the ablated nodule with no metabolically active lesion within. These findings showed that PET-CT is more sensitive than CECT in post-radiofrequency ablation assessment of pulmonary nodule. The hepatic focal lesion was detected in both PET-CT and contrast-enhanced CT studies despite of its faint contrast enhancement in CT.
CASE NO. (3)
History:
A 64 years old female patient who underwent surgical resection for pathologically proven colonic adenocarcinoma, presented with an elevated tumor marker. PET-CT and enhanced CT were done searching for distant metastasis and operative bed base-line assessment which discovered hepatic deposits. The patient received chemotherapy and radiotherapy & follow up 6 months later revealed a normal tumor marker level.
Assessment with PET-CT and CECT was done. The findings of the two modalities were compared.
CECT:
Fig.47: Axial post contrast CT images in arterial phase showing no enhancing focal lesion.
CECT:
Fig.48: Axial post contrast CT images in porto venous phase showing no enhancing focal lesion.
PET-CT:
Fig.49: Axial fused PET –CT images at the same level of the enhanced CT images showing metabolically active hepatic focal lesions (arrows).
CECT:
Fig.50: (a) axial post contrast CT image showing early post-operative enhancing scar and minimal thickening at the anastomotic site (arrows), (b) axial fused PET –CT image showing corresponding metabolic activity in the base line PET-CT (arrows).
Post therapeutic PET-CT:
Fig.51: (a,b) axial fused PET–CT images showing no metabolically active hepatic focal lesions, (c) axial post contrast CT image showing mild anastomotic site wall thickening (arrow) and (d) axial fused PET-CT image showing no anastomotic site metabolic activity (arrow).
Conclusion:
Post therapeutic PET-CT helped in detection of hepatic focal lesions that could not be detected by CECT, and explained elevated tumor markers level. Following chemotherapy, PET-CT showed good therapeutic response with disappearance of the metabolically active hepatic focal lesion as well as the post-surgical scar and anastomotic site activity.
CASE NO. (4)
History:
A 49 years old female patient with history of metastatic rectal cancer, received chemo and radiotherapy one year ago and no surgical interference was done.
Recently, she presented with intermittent constipation and elevated tumor markers.
Assessment with PET-CT and CECT was done. The findings of the two modalities were compared.
Fig.52: (a) axial post contrast CT image in lung window showing solitary right pulmonary nodule (arrow), (b) the same pulmonary nodule showing metabolic activity in axial PET-CT fused image (arrow).
Fig.53: (a) axial PET-CT image showing right hepatic metabolically active focal lesion (arrow), (b) this hepatic focal lesion could not be identified in axial post contrast CT image at the same level.
Fig.54: (a) axial post contrast CT image showing small sized right para aortic LN (arrow), (b) this LN appeares metabolically active in axial fused PET- CT image (arrow).
Fig.55: (a)axial post contrast CT image showing circumferential rectal wall faintly enhancing thickening with prominent surrounding lymphatic(arrow), (b) axial fused PET –CT showing avid metabolically activity of this lesion(arrow).
Conclusion:
Post therapeutic PET-CT helped in detection of hepatic focal lesion that could not be detected by contrast enhanced CT, as well as the small sized right para aortic lymph node which was considered normal regarding the lymph node size criteria.
Circumferential rectal thickening and the pulmonary nodule were detected in both PET-CT and contrast enhanced CT.
CASE NO. (5)
History:
A 38 years old female patient who underwent rectal surgical resection for pathologically proven adenocarcinoma, not followed by chemo or radiotherapy.
Recently, she presented with neck pain, low back pain and elevated tumor markers level.
Assessment with PET-CT and CECT was done. The findings of the two modalities were compared.
Fig.56: (a)axial CT image in bone window showing destructive cervical vertebral body lesion (arrow), (b)axial fused PET –CT image at the same level showing metabolically active lesion destroying the vertebral body of C2 as well as avid right deep cervical LN(arrows).
Fig.57: (a)axial CT image in bone window showing a small osteolytic lesion in the spinous process of the second lumber vertebra (arrow),
(b) axial fused PET –CT image at the same level showing metabolic activity within the lesion of the spinous process of the second lumber vertebra (arrow) .
Fig.58: (a),(b) and (c) axial post contrast CT images showing LNs and pulmonary masses(arrows). (d),(e) and (f)axial fused PET- CT images at the same levels showing metabolically active LNs and pulmonary masses (arrows).
Fig.59: (a)axial CT image in bone window showing right iliac bone osteolytic lesion (arrow), (b)axial fused PET- CT at the same level showing the right iliac bone metabolically active lesion (arrow).
Fig.60: (a) axial post contrast CT image at the level of rectal surgical interference and (b) axial fused PET-CT at the same level, both showing no masses or evidence of local recurrence.
Conclusion:
Post-therapeutic PET-CT helped in the detection of sizable pulmonary nodules as well as sizable lymph node, which were also detected by contrast-enhanced CT.
The bony osteolytic deposits were detected by contrast-enhanced CT as well as PET-CT.
CASE NO. (6)
History:
A 40 years old male patient who underwent rectal resection for pathologically proven mucinous adenocarcinoma, not followed by chemo or radiotherapy.
Follow- up revealed elevated level of tumor markers and multiple small hepatic focal lesions were detected by ultrasound, which were not present in the preoperative ultrasound or contrast-enhanced CT.
Assessment with PET-CT and CECT was done. The findings of the two modalities were compared.
Fig.61:(a)and(b) axial post contrast CT images showing multiple small sized hypodense non- enhancing hepatic focal lesions(arrows), (c) and (d)axial fused PET- CT images showing no avid metabolic hepatic focal lesions at the same levels .
Conclusion:
Non-enhancing hepatic focal lesions were detected in enhanced CT and could not be detected on PET-CT
Small hepatic focal lesions, as well as primary colonic mass having the pathology of mucinous adenocarcinoma, showed non-avid hepatic deposits.
CASE NO. (7)
History:
A 36 years old female patient who underwent hemicolectomy for pathologically proven mucinous adenocarcinoma, followed by chemotherapy.
Follow-up revealed elevated level of tumor markers and multiple hepatic focal lesions were detected by ultrasound, which were not present in the preoperative ultrasound or contrast- enhanced CT.
Assessment with PET-CT and CECT was done. The findings of the two modalities were compared.
Fig.62: (a)and(b) axial post contrast CT images showing two enhancing hepatic focal lesions(arrows), (c) and (d) axial fused PET-CT images showing no avid metabolic hepatic focal lesions at the same levels
Conclusion:
Non-enhancing hepatic focal lesions were detected in enhanced CT and could not be detected on PET-CT
Small hepatic focal lesions, as well as primary colonic mass having the pathology of mucinous adenocarcinoma, showed non-avid hepatic deposits.
CASE NO. (8)
History:
A 52 years old male patient who underwent surgical resection for pathologically proven colonic adenocarcinoma. The patient received chemotherapy and radiotherapy & follow up 6 months later revealed a normal tumor marker level. PET-CT and enhanced CT were done for post-therapeutic assessment. The findings of the two modalities were compared.
Fig.63: (a) axial post-contrast CT image showing operative bed fluid collection (seroma) with no enhancing component (arrow), (b) axial fused PET –CT image showing avid metabolic activity at the operative bed.
Conclusion:
PET-CT revealed metabolically active lesion at the operative bed due to FDG accumulation in inflamed tissue in the post-surgical region.
CASE NO. (9)
History:
A 55 years old female patient who underwent surgical resection for pathologically proven colonic adenocarcinoma, presented with an elevated tumor marker. PET-CT and enhanced CT were done searching for distant metastasis and operative bed base-line assessment which discovered hepatic deposits.
Assessment with PET-CT and CECT was done. The findings of the two modalities were compared.
Fig.64: (a)axial post contrast CT images in porto venous phase showing no enhancing focal lesion ,(b) axial fused PET –CT image at the same level of the enhanced CT images showing metabolically active hepatic focal lesions (arrows).
Fig.65: (a) axial post contrast CT images showing small subcentimetric common iliac lymph node , (b) this LN appeares metabolically active in axial fused PET- CT image (arrow).
Conclusion:
PET-CT helped in detection of hepatic focal lesion that could not be detected by contrast enhanced CT, as well as the small sized lymph node which was considered normal regarding the lymph node size criteria.
CASE NO. (10)
History:
A 41 years old male patient who underwent rectal resection for pathologically proven adenocarcinoma, not followed by chemo or radiotherapy.
Follow- up revealed elevated level of tumor markers and multiple hepatic masses were detected by ultrasound, which were not present in the preoperative ultrasound or contrast-enhanced CT.
Assessment with PET-CT and CECT was done. The findings of the two modalities were compared.
Fig.66: (a) axial post contrast CT image showing multiple hypodense non- enhancing hepatic focal lesions(arrows), (b) axial fused PET- CT images showing avid metabolic hepatic focal lesions at the same levels .
Conclusion:
PET-CT helped in detection of hepatic focal lesion that could not be detected by contrast enhanced CT.
DISCUSSION
DISCUSSION
Enhanced computed tomography is considered an anatomic imaging modality, and it plays an important role in the detection of post therapeutic recurrence in patient with cancer colon. Limitations of enhanced CT are due to its reliance on size criteria in the diagnosis of metastatic LNs, enhancing pattern of hepatic deposits and the great limitation is the inability to differentiate between post- therapeutic viable and non-viable malignant lesion.
PET /CT has been reported to play an important role in early detection of post therapeutic recurrence in patients with cancer colon due to its direct evaluation of malignant cellular metabolism. Its great role appears in detection of small sized LNs, local operative bed recurrence, small supra renal metastasis, early osseous deposits and post- therapeutic evaluation of viable and non-viable malignant lesions(post chemotherapy and radiotherapy). Limitations of PET/CT include its inability to detect viability in sub centimetric hepatic focal lesions and pulmonary nodules as well as the evaluation of mucinous tumor deposits, particularly in hypo cellular lesions with abundant mucin.
The final diagnosis of distant metastasis and/or local recurrence in post- therapeutic cancer colon based on lesions analysis was evident in 70% of our patient population with sensitivity of 95.6% ,specificity of 91.4% , (NPV) of 88.9%, (PPV) of 96.7% , and diagnostic efficacy of 94.4%.
These results agreed with results obtained in the study done by (Metser et al .,2010) which included 158 patients who had a history of colorectal carcinoma , presented with increasing CEA levels and conventional imaging modalities revealed an equivocal explanation of the elevated CEA level.
The sensitivities of PET/CT and MDCT were 98.1% and 66.7%, the specificities were 75% and 62.5% respectively. The specificity in (Metser et al.,2010) study by PET/CT and CT was higher than the study by (Mittal et al.,2011) in which he analyzed 73 patients (55 male, 18 female; age range 25 to 80 years) histopathologically proven CRC who underwent FDG PET/CT imaging for the detection of recurrence after the initial treatment. Rising CEA levels were detected in 51 patients. In 13 patients, CT was negative, whereas PET was positive (three patients with liver lesions, five patients with lymph nodes involvement , two patients with bone metastases, one patient with local recurrence in urinary bladder wall, one patient with lymph node and liver metastases, and one patient with lymph node and bone metastases), thereby changing the management.
As reported in the study done by (Chen et al.,2007) and confirmed in our study , in 56 patients with recurrent and/or metastatic CRC, sensitivity of PET/CT in diagnosis CRC recurrence and/or metastasis was 94.6%, specificity was 83.3%, positive predictive value was 96.4% and negative predictive value was 76.9%. PET/CT imaging detected occult malignant lesions in eight cases where CT showed negative findings. Furthermore, it detected more lesions than CT did in 30.4% of cases (17/56). Recurrence and/or metastasis were detected by 18F-FDG PET/CT imaging in 91.7% of cases (22/24) having elevated serum CEA levels.
The study results by (Choi et al., 2010) to assess the value of 18F-FDG PET/CT in detecting local or distant recurrence in 269 CRC patients operated for colorectal cancer and to compare the accuracy with conventional imaging studies, showed overall sensitivity, specificity, accuracy, PPV, and NPV of 94.7%, 96.0%, 95.8%,78.2%, and 99.2% for PET/CT, and 86.8%, 97.6%,96.2%, 84.6%, and 98.0% for conventional imaging studies, respectively .
On a region-based analysis in the study by (Choi et al ., 2010), PET/CT detected more lesions compared to conventional imaging studies in local recurrence (14/15 vs. 13/15) and peritoneal carcinomatosis (4/4 vs. 3/4). PET/CT and conventional imaging studies detected the same number of lesions in abdominal lymph nodes (8/8) and hepatic (13/13) metastases. PET/CT additionally detected metastases to the lung (n = 5) and bone (n = 1). Both PET/CT and conventional imaging studies showed a false positive finding in a case for single spleen metastasis that was pathologically proven to be chronic inflammation.
As reported previously and confirmed by our study (Chiewvit et al., 2013) have shown that 18F-FDG PET/CT is a useful method in postoperative evaluation of patients with suspected recurrent colorectal cancerous lesions and a normal CEA level. When conventional imaging methods have shown equivocal findings, 18F-FDG PET/CT is effective and helpful to distinguish local recurrences or metastases from postoperative changes or benign disease findings that may not be meaningful.
Previous studies as described above have shown the role of PET/CT in the detection of post therapeutic cancer colon recurrence with better sensitivity and specificity when compared to that of CT scan. By using PET/CT, studies demonstrated more information and lesion characterization. Comparing PET/CT to CT, the present study also shows comparable overall sensitivity, specificity and diagnostic efficacy.
SUMMARY
&
CONCLUSION
SUMMARY & CONCLUSION
Enhanced CT relies on anatomic changes for primary diagnosis, staging and follow-up after chemotherapy and radiotherapy, PET-CT gives anatomic and metabolic information.
18F-FDG PET-CT plays an important role in the early detection of distant metastases, local recurrence and evaluation of post chemotherapy and radiotherapy tumor viability in patients with colorectal cancer.
Strict adherence to standardized protocols, technical procedures and good patient preparation are essential requirements to obtain optimum results.
In our study, PET/CT and enhanced CT, both, early detected hepatic deposits, pulmonary masses, suprarenal deposits, sizable LNs and bone deposits. PET/CT provided useful information and had a considerable impact on disease management in a greater proportion of patients, enabling the detection of recurrent disease as early as possible with high accuracy in assessment of therapeutic response. It detected viable residual tumor cells in operative bed scar, small LNs, hepatic focal lesion, peritoneal deposits, pulmonary masses, bone deposits and supra renal deposits avoiding unnecessary surgeries .
PET/CT is a better method to evaluate post-therapeutic colorectal cancer patients with suspected tumor recurrence or distant metastasis than enhanced CT with significantly higher specificity and sensitivity.
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