¹⁸Fluorodeoxyglucose PET Is Prognostic of Progression-Free and Overall Survival in Locally Advanced Pancreas Cancer Treated With Stereotactic Radiotherapy

Purpose

This study analyzed the prognostic value of positron emission tomography (PET) for locally advanced pancreas cancer patients undergoing stereotactic body radiotherapy (SBRT).

Patients and Methods

Fifty-five previously untreated, unresectable pancreas cancer patients received a single fraction of 25-Gy SBRT sequentially with gemcitabine-based chemotherapy. On the preradiation PET-CT, the tumor was contoured and the maximum standardized uptake value (SUVmax) and metabolic tumor burden (MTB) were calculated using an in-house software application. High-SUVmax and low-SUVmax subgroups were created by categorizing patients above or below the median SUVmax. The analysis was repeated to form high-MTB and low-MTB subgroups as well as clinically relevant subgroups with SUVmax values of <5, 5–10, or >10. Multivariate analysis analyzing SUVmax, MTB, age, chemotherapy cycles, and pretreatment carbohydrate antigen (CA)19-9 was performed.

Results

For the entire population, median survival was 12.7 months. Median survival was 9.8 vs.15.3 months for the high- and low- SUVmax subgroups (p <0.01). Similarly, median survival was 10.1 vs. 18.0 months for the high MTB and low MTB subgroups (p <0.01). When clinical SUVmax cutoffs were used, median survival was 6.4 months in those with SUVmax >10, 9.5 months with SUVmax 5.0–10.0, and 17.7 months in those with SUVmax <5 (p <0.01). On multivariate analysis, clinical SUVmax was an independent predictor for overall survival (p = 0.03) and progression-free survival (p = 0.03).

Conclusion

PET scan parameters can predict for length of survival in locally advanced pancreas cancer patients.

Introduction

Pancreas cancer is the fourth most common cause of cancer deaths in the United States (1). For those who present with unresectable disease, no curative treatment exists. The role of radiotherapy is debated 2, 3, 4, 5, 6. Even when high radiation doses are given and local tumor control is achieved, most patients die from distant disease progression 7, 8, 9, making the value of local treatment uncertain.

Currently, there are no pretreatment clinical or pathologic characteristics that can predict for disease behavior and clinical prognosis in pancreas cancer. As such, this study was performed to determine whether preradiation positron emission tomography (PET) scan parameters such as maximum selective uptake value (SUVmax) and total metabolic tumor burden (MTB), which is a measure of the total amount of glucose uptake within the tumor, were of prognostic value in locally advanced pancreas cancer patients treated with chemotherapy and stereotactic body radiotherapy (SBRT). Prior studies have shown pretreatment PET parameters to be prognostic for other disease sites including lung and head and neck 10, 11. By identifying a subset of pancreas cancer patients with longer life expectancies, future therapeutic approaches could be tailored appropriately. For example, those with better prognosis may benefit most from local disease control with both chemotherapy and radiation. Those with poorer prognosis, who would undergo more rapid disease progression, might instead benefit from more intensive chemotherapy as the primary treatment.