Mark Tann

Response Criteria in Oncologic Imaging: Review of Traditional and New Criteria

There has been a proliferation and divergence of imaging-based tumor-specific response criteria over the past 3 decades whose purpose is to achieve objective assessment of treatment response in oncologic clinical trials. The World Health Organization (WHO) criteria, published in 1981, were the first response criteria and made use of bidimensional measurements of tumors. The Response Evaluation Criteria in Solid Tumors (RECIST) were created in 2000 and revised in 2009. The RECIST criteria made use of unidimensional measurements and addressed several pitfalls and limitations of the original WHO criteria. Both the WHO and RECIST criteria were developed during the era of cytotoxic chemotherapeutic agents and are still widely used. However, treatment strategies changed over the past decade, and the limitations of using tumor size alone in patients undergoing targeted therapy (including arbitrarily determined cutoff values to categorize tumor response and progression, lack of information about changes in tumor attenuation, inability to help distinguish viable tumor from nonviable components, and inconsistency of size measurements) necessitated revision of these criteria. More recent criteria that are used for targeted therapies include the Choi response criteria for gastrointestinal stromal tumor, modified RECIST criteria for hepatocellular carcinoma, and Immune-related Response Criteria for melanoma. The Cheson criteria and Positron Emission Tomography Response Criteria in Solid Tumors make use of positron emission tomography to provide functional information and thereby help determine tumor viability. As newer therapeutic agents and approaches become available, it may be necessary to further modify existing anatomy-based response-assessment methodologies, verify promising functional imaging methods in large prospective trials, and investigate new quantitative imaging technologies.

A Pilot Trial of Serial 18F-Fluorodeoxyglucose Positron Emission Tomography in Patients With Medically Inoperable Stage I Non–Small-Cell Lung Cancer Treated With Hypofractionated Stereotactic Body Radiotherapy

PURPOSE Routine assessment was made of tumor metabolic activity as measured by 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in Stage I non-small-cell lung cancer (NSCLC). This report describes PET correlates prospectively collected after stereotactic body radiotherapy (SBRT) for patients with medically inoperable NSCLC. METHODS AND MATERIALS 14 consecutive patients with medically inoperable Stage I NSCLC were enrolled. All patients received SBRT to 60-66 Gy in three fractions. Patients underwent serial planned FDG-PET/computed tomography fusion imaging before SBRT and at 2, 26, and 52 weeks after SBRT. RESULTS With median follow-up of 30.2 months, no patients experienced local failure. One patient developed regional failure, 1 developed distant failure, and 1 developed a second primary. The median tumor maximum standardized uptake value (SUV(max)) before SBRT was 8.70. The median SUV(max) values at 2, 26, and 52 weeks after SBRT were 6.04, 2.80, and 3.58, respectively. Patients with low pre-SBRT SUV were more likely to experience initial 2-week rises in SUV, whereas patients with high pre-SBRT SUV commonly had SUV declines 2 weeks after treatment (p = 0.036). Six of 13 patients had primary tumor SUV(max) >3.5 at 12 months after SBRT but remained without evidence of local disease failure on further follow-up. CONCLUSIONS A substantial proportion of patients may have moderately elevated FDG-PET SUV(max) at 12 months without evidence of local failure on further follow-up. Thus, slightly elevated PET SUV(max) should not be considered a surrogate for local treatment failure. Our data do not support routine serial FDG-PET/computed tomography for follow-up of patients receiving SBRT for Stage I NSCLC.

State-of-the-Art Pancreatic MRI

OBJECTIVE The purpose of this article is to discuss the most current techniques used for pancreatic imaging, highlighting the advantages and disadvantages of state-of-the-art and emerging pulse sequences and their application to pancreatic disease. CONCLUSION Given the technologic advances of the past decade, pancreatic MRI protocols have evolved. Most sequences can now be performed in one or a few breath-holds; 3D sequences with thin, contiguous slices offer improved spatial resolution; and better fat and motion suppression allow improved contrast resolution and image quality. The diagnostic potential of MRCP is now almost as good as ERCP, with pancreatic MRI as the main imaging technique to investigate biliopancreatic pain, chronic pancreatitis, and cystic pancreatic tumors at many institutions. In addition, functional information is provided with secretin-enhanced MRCP.

Computed Tomography Demonstration of Lipomatous Metaplasia of the Left Ventricle Following Myocardial Infarction

Replacement of myocardium by fat, particularly of the right ventricle, is often diagnosed as arrhythmogenic right ventricular dysplasia. At autopsy, however, 68% of scars associated with chronic ischemic heart disease have shown fatty metaplasia in the scar. Four patients with a past history of previous myocardial infarctions and computed tomography demonstration of fatty change in left ventricular regions of hypokinesis and infarction are presented. It is proposed that these findings represent ischemic fatty metaplasia, an alternative etiology of fatty tissue replacing myocardium.

Peritoneal and Retroperitoneal Anatomy and Its Relevance for Cross-Sectional Imaging

It is difficult to identify normal peritoneal folds and ligaments at imaging. However, infectious, inflammatory, neoplastic, and traumatic processes frequently involve the peritoneal cavity and its reflections; thus, it is important to identify the affected peritoneal ligaments and spaces. Knowledge of these structures is important for accurate reporting and helps elucidate the sites of involvement to the surgeon. The potential peritoneal spaces; the peritoneal reflections that form the peritoneal ligaments, mesenteries, and omenta; and the natural flow of peritoneal fluid determine the route of spread of intraperitoneal fluid and disease processes within the abdominal cavity. The peritoneal ligaments, mesenteries, and omenta also serve as boundaries for disease processes and as conduits for the spread of disease.

Disconnected pancreatic duct syndrome: Imaging findings and therapeutic implications in 26 surgically corrected patients

Purpose The lack of ductal continuity between a viable pancreatic tissue and the gastrointestinal tract results in the disconnected pancreatic duct syndrome (DPDS). The purpose of our study is to describe accurately the imaging features of CT scanning and endoscopic retrograde pancreatography (ERCP) that define the DPDS. Methods We conducted a retrospective analysis of the computed tomography (CT) and ERCP examinations in 26 consecutive patients with surgically proven disconnected pancreatic ducts treated over a 5-year period at our institution. Two abdominal radiologists concurrently defined the imaging features (presence and size of fluid collection along the course of the pancreatic duct, upstream enhancing pancreatic parenchyma, and ERCP abnormalities) via consensus for both exams. Patient demographics, etiology of pancreatitis, surgical treatment, initial CT interpretation, and the delay between symptom onset to correct diagnosis were recorded. Results A discrete, intrapancreatic fluid collection (average size = 27 cm2 (range, 4–74 cm2) along the course of the main pancreatic duct with upstream viable pancreatic parenchyma was identified by CT in 26 cases. ERCP showed ductal obstruction at the level of the intrapancreatic fluid collection in all patients with extravasation of contrast in 14 (54%). All patients were treated by operation: 15 (58%) by internal drainage into a Roux-en-Y limb of jejunum and 11 (42%) by distal pancreatic resection. No prior CT interpretation correctly identified DPDS. The average delay between symptom onset and definitive diagnosis was 9.3 months (range, 3–36 months). Conclusions A discrete intrapancreatic fluid collection along the expected course of the main pancreatic duct with viable upstream pancreatic parenchyma suggests the diagnosis of DPDS. ERCP findings of ductal obstruction at the level of this fluid collection with or without contrast extravasation confirm this diagnosis. Treatment is surgical and requires either internal drainage or distal pancreatic resection for complete resolution.

Use of diffusion-weighted MRI to differentiate chronic pancreatitis from pancreatic cancer

OBJECTIVE The purpose of this study was to compare diffusion-weighted MRI (DWI) and conventional (non-DWI) MRI sequences in differentiating mass-forming chronic pancreatitis from pancreatic cancer. MATERIALS AND METHODS A retrospective cohort study included 36 patients who underwent pancreatic resection for pancreatic cancer (n = 13) and chronic pancreatitis (n = 23) after preoperative MRI with DWI. Two independent reviewers assessed the DW images for signal intensity and apparent diffusion coefficient (ADC) values. Four weeks later, they reviewed the other MR images for size of mass, double-duct sign, pancreatic duct cutoff, and perivascular soft-tissue cuffing. A score for conventional MRI was given with 1 meaning definitely benign and 5 meaning definitely malignant. Univariate and multivariate analyses and receiver operating characteristic (ROC) curve analysis were performed with surgical pathologic examination as the reference standard. RESULTS The only finding that differentiated the two groups was the presence of a well-defined mass, favoring the diagnosis of cancer (p = 0.02, p < 0.01). There was no significant difference between the two groups in signal intensity on DW images (p = 0.82, p = 0.85) or ADC (p = 0.51, p = 0.76). Double-duct sign, pancreatic duct cutoff, and perivascular soft-tissue cuffing were not useful in differentiating the two groups. The areas under the ROC curve were 0.873 and 0.878 for the conventional MRI scores, compared with 0.602 and 0.552 for ADC measurements (p = 0.02, p = 0.008). CONCLUSION The addition of DWI to conventional MRI does not facilitate differentiation of pancreatic cancer from chronic pancreatitis.

Can FDG-PET be used to predict growth of stage I lung cancer?

AIM To determine the relationship between the metabolic activity measured by 2-[(18)F]-fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET) and computed tomography (CT)-derived tumour growth rates for stage 1 lung cancer. METHODS Stage I lung cancer patients at our institution who underwent FDG PET, and who had at least two pre-treatment chest CT examinations (n=51), were retrospectively identified. Metabolic activity was defined by maximum lesion standardized uptake value (SUV) and maximum lesion-to-mean background activity (LBR). Growth rates were determined from serial CT volume measurements and the doubling time (DT) was calculated. Tumour growth rates were divided into rapid (DT<180 days), intermediate (DT=180-270 days), and slow (DT>270 days) groups. RESULTS Rapid, moderate, and slow DT were seen in 22, 19, and 10 patients, respectively. Means (standard deviations) of SUV in the three groups (from rapid to slow growth rate) were 8.2 (4.8), 5.5 (4.5), and 2.2 (1.1), respectively and of LBR were 22.7 (10.1), 15.1 (12.6), and 6 (2.6), respectively. There was a significant relationship between SUV and DT (p<0.05), as well as between LBR and DT (p<0.05). CONCLUSIONS For stage I lung tumours, there is a significant relationship between growth rates, as measured by serial CT examinations, and the initial pre-treatment metabolic activities, as measured by FDG uptake. This suggests that in patients in whom it is difficult to decide on the aggressiveness on treatment, FDG-PET may be used as additional prognostic tool for determining management.

Imaging of the pancreas with secretin enhancement.

Magnetic resonance cholangiopancreatography is a noninvasive imaging technique for evaluation of the pancreatic duct and the biliary tree. Secretin is a polypeptide hormone that has numerous physiological effects, including stimulation of the pancreatic secretion of bicarbonate-rich fluid and transient increase in the tone in the sphincter of Oddi. As a result, secretin administration usually results in distention of the pancreatic duct; therefore, visualization of the pancreatic ductal anatomy is often substantially improved. Awareness of its value by referring clinicians and radiologists will increase its use in the future.

The Impact of Image Reconstruction Bias on PET/CT 90Y Dosimetry After Radioembolization

PET/CT imaging after radioembolization is a viable method for determining the posttreatment 90Y distribution in the liver. Low true-to-random coincidence ratios in 90Y PET studies limit the quantitative accuracy of these studies when reconstruction algorithms optimized for traditional PET imaging are used. This study examined these quantitative limitations and assessed the feasibility of generating radiation dosimetry maps in liver regions with high and low 90Y concentrations. Methods: 90Y PET images were collected on a PET/CT scanner and iteratively reconstructed with the vendor-supplied reconstruction algorithm. PET studies on a Jaszczak cylindric phantom were performed to determine quantitative accuracy and minimum detectable concentration (MDC). 90Y and 18F point-source studies were used to investigate the possible increase in detected random coincidence events due to bremsstrahlung photons. Retrospective quantitative analyses were performed on 90Y PET/CT images obtained after 65 right or left hepatic artery radioembolizations in 59 patients. Quantitative image errors were determined by comparing the measured image activity with the assayed 90Y activity. PET images were converted to dose maps through convolution with voxel S values generated using MCNPX, a Monte Carlo N-particle transport code system for multiparticle and high-energy applications. Tumor and parenchyma doses and potential bias based on measurements found below the MDC were recorded. Results: Random coincidences were found to increase in 90Y acquisitions, compared with 18F acquisitions, at similar positron emission rates because of bremsstrahlung photons. Positive bias was observed in all images. Quantitative accuracy was achieved for phantom inserts above the MDC of 1 MBq/mL. The mean dose to viable tumors was 183.6 ± 156.5 Gy, with an average potential bias of 3.3 ± 6.4 Gy. The mean dose to the parenchyma was 97.1 ± 22.1 Gy, with an average potential bias of 8.9 ± 4.9 Gy. Conclusion: The low signal-to-noise ratio caused by low positron emission rates and high bremsstrahlung photon production resulted in a positive bias on 90Y PET images reconstructed with conventional iterative algorithms. However, quantitative accuracy was good at high activity concentrations, such as those found in tumor volumes, allowing for adequate tumor 90Y PET/CT dosimetry after radioembolization.