Lymphoma: Differences between SUVmax and SUVpeak for Therapy Response Assessment

PET•CT is used for evaluation of chemotherapy response in lymphoma.

Partha Ghosh, MD

Case study data provided by National University Hospital, Singapore


 |  2012-10-25

Introduction

Fludeoxyglucose F 18* (18F FDG) PET•CT is widely used for evaluation of chemotherapy response in lymphoma. Standardized uptake value change in involved lymph nodal groups have been the major quantitative indicator of early therapy response assessment since nodal volume and size on CT is often slower to decrease following successful therapy. Presence of  post-therapy residual mass without metabolically active tumor is a common finding in lymphoma (Kasamon et al J Nucl Med 2007; 48:19S–27S).

 

*Siemens’ PETNET Solutions is a manufacturer of fludeoxyglucose F 18 injection (18F FDG). Indication and important safety information as approved by the US Food and Drug Administration can be found at the bottom of the page for 18F FDG, adult dose 5-10 mCi, administered by intravenous injection.

 

History & Diagnosis
A 60-year-old man presented with left supraclavicular lymph nodal swelling and was diagnosed as Hodgkin’s lymphoma.The patient had initial staging PET•CT (Sept. 28, 2010) performed on a Biograph™ mCT with ultraHD•PET that showed multiple 18F FDG-avid left supraclavicular and axillary nodes. There was no evidence of involvement of other lymph nodal groups or systemic involvement. The patient was subjected to chemotherapy and underwent a repeat PET•CT (Nov. 4, 2010) immediately following first cycle of ABVD (Adriamycin, bleomycin, vinblastine and dacarbazive) chemotherapy. The second scan showed no significant change in size or intensity of 18F FDG uptake as compared to the first study. SUVmax of the largest supraclavicular lymph node lesion decreased from 14.3 to 9.09 (36% decrease). Although there was no visual change in size of lesions as well as intensity, the 36% decrease in SUVmax following the first cycle supported the physician’s decision to continue therapy. A subsequent PET•CT performed after a further cycle of chemotherapy showed no change in size and intensity of 18F FDG uptake in the nodal lesions. SUVmax, however, increased from 9.09 to 10.64 in the same supraclavicular node suggesting no significant impact of two consecutive chemotherapy cycles. Analysis of SUVpeak values (Fig. 1 and 2), however, was more representative of the actual response level of the lymphomatous lesions.

 

Fig. 1
Images show sequential whole-body PET images reflecting absence of significant visible change in lesion size and intensity. The fused PET•CT axial slices highlighting the supraclavicular nodal lesion shows the volume of interest (VOI) defined around the metabolic activity in the node with the SUVmax as well as SUVpeak, which is defined as the average SUV within a 1 cubic cm volume within the region of the tumor with the highest metabolic activity. As shown in the image at left, there is a significant difference between SUVmax and SUVpeak. The difference in SUVpeak between the initial and the second scan following one cycle of chemotherapy is 24%, which is closer to the actual level of response.

 

Fig. 2
The third study shows minor increase in SUVmax as well as SUVpeak, which confirms the visual impression that therapy after two cycles had not been effective. In view of the visual and quantitative evidence of lack of response after two cycles of ABVD chemotherapy, a modification in chemotherapy is warranted in this patient. Examination Protocol: 8 mCi 18F FDG injection; 60 minutes post-injection delay; 1 minute per bed PET acquisition.

Comments
Maximum SUV value (SUVmax) or average SUV value within a 3D region of interest (ROI) defined around an involved nodal group has been measured during sequential evaluation and  percentage change in these values have been used to judge therapy response. SUVmax can be considered to be a single-pixel ROI. SUVmax is highly dependent on the statistical quality of the images and the size of the maximal pixel. SUVmax variability increases with the matrix size as well as the decrease in count statistics (Wahl et al JNM 2009; 50:122S- 150S). The measured activity concentration in a small volume of a PET image depends on the activity in neighboring voxels. Activity levels in the neighboring voxels may cause a spill-in or spill-out of activity in any voxel being evaluated for SUV. This partial volume effect is the reason SUVmax within a tumor ROI is subject to inaccuracies. Although the SUVmax represents the maximum metabolic activity of the tumor and variations in SUVmax logically represents the most clinically relevant change due to therapy, practically the reliability of SUVmax as a  single pixel measurement is subject to fluctuations. SUVs obtained from larger, fixed ROIs are more reproducible than single pixel SUVs as is usual for calculation of SUVmax. SUVpeak measurements (a circular volume with fixed diameter, e.g 1 cm, in the hottest area of the tumor) is more reproducible since it involves the mean value of a few pixels involving and surrounding the hottest tumor area. This makes it close to SUVmax in terms of its representation of the maximum tumor metabolism, yet it could avoid the statistical fluctuations of  SUVmax due to incorporation of a larger number of pixels within the hottest tumor area. Velasquex et al (J Nucl Med. 2009 Oct;50(10):1646-54.) assessed the repeatability of SUVmax, SUVpeak and SUVmean in 62 patients in a multicenter phase I oncology trial who underwent double baseline 18F FDG-PET studies. The variation of SUVmax values between two baseline studies was much larger than SUVpeak and SUVmean. This suggests that values involving a region with multiple pixels are more statistically reproducible and dependable for clinical trials.
This clinical example of sequential imaging during chemotherapy in a case of Hodgkin’s lymphoma illustrates the significant difference between SUVmax and SUVpeak values and its impact on response evaluation.

 

*Fludeoxyglucose F 18 Injection
INDICATIONS AND USAGE

Fludeoxyglucose F 18 injection (18F FDG) is indicated for positron emission tomography (PET) imaging in the following setting:
Oncology: For assessment of abnormal glucose metabolism to assist in the evaluation of malignancy in patients with known or suspected abnormalities found by other testing modalities, or in patients with an existing diagnosis of cancer.
 

IMPORTANT SAFETY INFORMATION
Radiation Risks

Radiation-emitting products, including fludeoxyglucose F 18 injection, may increase the risk for cancer, especially in pediatric patients. Use the smallest dose necessary for imaging and ensure safe handling to protect the patient and health care worker.
 

Blood Glucose Abnormalities
In the oncology and neurology setting, suboptimal imaging may occur in patients with inadequately regulated blood glucose levels. In these patients, consider medical therapy and laboratory testing to assure at least two days of normoglycemia prior to fludeoxyglucose F18 injection administration.
 

Adverse Reactions
Hypersensitivity reactions with pruritus, edema and rash have been reported; have emergency resuscitation equipment and personnel immediately available.

 

Full Prescribing Information for Fludeoxyglucose F 18 Injection

 

Fludeoxyglucose F 18 injection is manufactured by Siemens' PETNET Solutions, 810 Innovation Drive, Knoxville, TN 39732
 

The statements by Siemens customers described herein are based on results that were achieved in the customer's unique setting. Since there is no "typical" hospital and many variables exist (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results.