PET Imaging for Treatment Response in Cancer

Abstract

KeywordsPET; FDG; Cancer imaging; Response imaging PET tumor surveys have become widely used in clinical practice. [F-18] fluorodeoxyglucose (FDG) is the most commonly used radiotracer for clinical indication of tumor staging and restaging after treatment. FDG PET consistently has exhibited better diagnostic performance than conventional imaging in adults and pediatric populations. [1][2][3][4] More recently, a growing body of literature is reporting the use of FDG and other PET imaging agents in treatment response assessment. [5][6][7] In many cases, FDG PET has proved to be a reliable means of noninvasively observing response in various treatments.Additionally, reliable determination of past treatment changes, including recurrent tumors and differentiation of benign and malignant lesions, will reduce morbidity and the cost of care in anatomic imaging. The Response Evaluation Criteria in Solid Tumors (RECIST) are a useful means to report quantitative changes in tumor size on CT scans in many different tumors in response to treatment. 8,9,10 Many tumor types, however, do not change size appreciably in response to treatment. Early changes that may indicate treatment regimen effectiveness also may not result in tumor change in size. FDG PET is a relatively sensitive indicator of treatment response in many tumors, indicating changes in metabolism that often precede or take the place of tumor size change. Fig. 1 shows some examples of FDG PET tumor response.Recently, several cooperative groups have addressed the use of FDG PET as a biomarker for cancer treatment response. An early report by the European Organization for Research and Treatment of Cancer (EORTC) set criteria for treatment response according to changes in tumor FDG uptake compared to baseline. 2 These criteria include:Complete response (CR)- [F-18] fluorodeoxyglucose uptake is comparable to baseline activity in all lesions Partial response (PR)-all target lesions have greater than 25% decrease in standardized uptake variable (SUV) Stable disease (SD)-target lesions have less than 25% increase or decrease in SUV Progressive disease (PD)-at least one target lesion has greater than 25% increase in SUV, or new lesions appear (regardless of SUV changes in target lesions)These criteria are in wide use today for clinical FDG PET imaging. A set of criteria for clinically significant changes in tumor FDG uptake, however, is based on consistent parameters for the FDG PET acquisition between studies in the same patient, and between patient imaging groups at different institutions. Development and evaluation of new cancer therapies could be enhanced by a set of validated biomarkers for treatment response. FDG PET meets these criteria in clinical studies, if imaging studies are conducted with patients on clinical therapeutic trials in a reliable and consistent manner. 3 To address the consistency in FDG PET data for use as NIH Public Access A review of cancer treatment response begins with consideration of the pathological basis of the tumor process. Tumors are c...

The predictive value of 18F-FDG PET/CT for assessing pathological response and survival in locally advanced rectal cancer after neoadjuvant radiochemotherapy

“…However, to facilitate the comparison of our data with those of previously published studies, we repeated the analysis comparing TRG1-2 and TRG3-5, and found AUCs of 0.68 (95 % CI 0.57 -0.78) and 0.66 (95 % CI 0.56 -0.77) for early and late RIs, respectively. Second, we calculated tumour SUVmax changes as a quantitative parameter of metabolic response because this value is less observer-dependent and more reproducible than SUVmean which is dependent on the dimensions of the region of interest [45,46]. Finally, we used visual assessment (complete vs. incomplete metabolic response) only for the late PET/CT scan because when evaluating PET for early response to treatment, metabolic changes may be subtle and not visually evident.…”

Reliability of Quantitative 18F-FDG PET/CT Imaging Biomarkers for Classifying Early Response to Chemoradiotherapy in Patients With Locally Advanced Non–Small Cell Lung Cancer

“…Treatment response assessments using PET/CT can provide a functional assessment of tumor biology in addition to an anatomical characterization of tumor size. 13,14 However, in order to successfully integrate research-derived analysis methods into the standard clinical response assessment, analysis protocols will need to be streamlined to minimize their impact on the clinical workflow. In addition, image-based metrics need to be universally applicable so that they will yield consistent results between sites irrespective of scanner technology, reconstruction algorithm, analysis software package, observer, and so on; and harmonization initiatives are underway in Europe, 34 Japan, 35 and the United States.…”

“…PET/CT is being used more frequently for imaging-based response assessments, as it can supplement anatomical characterization with a functional assessment of tumor biology, which is important as changes in tumor size may lag behind changes in tumor physiology, especially early in therapy. 13,14 Specifically, 18 F-FDG PET/CT has been adopted for early response assessment during chemoradiotherapy in LA-NSCLC. 15,16 Local recurrences after radiation treatment tend to occur inside tumor regions demonstrating high 18 F-FDG avidity on midtreatment PET scans, and as such, high tumor metabolic activity midway through fractionated radiation therapy is associated with poorer clinical outcomes.…”

F-18 FDG PET/CT in Rectal Carcinoma

“…It chose an RI cut off of 25% but it did not take into consideration the different types of therapy (radio or chemotherapy, adjuvant or neoadjuvant). 15,17 These proposals are not universally agreed upon yet, with 2 main problems remaining: (1) to define the timing, that is the interval between the end of therapy and FDG PET/CT; (2) to define the cut off, that is the RI value above which a patient must be considered a responder. To solve these points many studies should be performed to consider every type of cancer and every possible therapeutic modality.…”

“…14 It is worth noting that measurement of maximum SUV (SUV max ) is mandatory because its value is the most consistent and less dependent on region of interest dimension. 7,15 Nevertheless, because SUV max value depends on many other factors (patient weight, interval time between FDG administration and acquisition, blood glucose level), it must be evaluated carefully to achieve correct interpretation. 7 In particular, when SUV max pre-and posttherapy are compared to assess the metabolic response, percentage difference between pre-and post-response index (RI) must be considered keeping in mind that differences of up to 20% fall into the statistical variation range.…”