Addressing glucose sensitivity measured by F-18 FDG PET in lung cancers for radiation treatment planning and monitoring

Time-course of effects of external beam radiation on [18F]FDG uptake in healthy tissue and bone marrow

The utility of PET for monitoring responses to radiation therapy have been complicated by metabolically active processes in surrounding normal tissues. We examined the time‐course of [¹⁸F]FDG uptake in normal tissues using small animal‐dedicated PET during the 2 month period following external beam radiation. Four mice received 12 Gy of external beam radiation, in a single fraction to the left half of the body. Small animal [¹⁸F]FDG‐PET scans were acquired for each mouse at 0 (pre‐radiation), 1, 2, 3, 4, 5, 8, 12, 19, 24, and 38 days following irradiation. [¹⁸F]FDG activity in various tissues was compared between irradiated and non‐irradiated body halves before, and at each time point after irradiation. Radiation had a significant impact on [¹⁸F]FDG uptake in previously healthy tissues, and time‐course of effects differed in different types of tissues. For example, liver tissue demonstrated increased uptake, particularly over days 3–12, with the mean left to right uptake ratio increasing 52% over mean baseline values (p<0.0001). In contrast, femoral bone marrow uptake demonstrated decreased uptake, particularly over days 2–8, with the mean left to right uptake ratio decreasing 26% below mean baseline values (p=0.0005). Significant effects were also seen in lung and brain tissue. Radiation had diverse effects on [¹⁸F]FDG uptake in previously healthy tissues. These kinds of data may help lay groundwork for a systematically acquired database of the time‐course of effects of radiation on healthy tissues, useful for animal models of cancer therapy imminently, as well as interspecies extrapolations pertinent to clinical application eventually.

PACs Number: 87.50.‐a

Correcting tumour SUV for enhanced bone marrow uptake: retrospective 18F-FDG PET/CT studies

PURPOSE

The concentration of F-FDG in the bone marrow is usually low. One common cause of high uptake is due to bone marrow stimulating drugs administered in conjunction with chemotherapy or radiation therapy. It has been hypothesized that the sequestration of F-FDG to the bone marrow may reduce the standardized uptake value (SUV) of a tumour. We tested this hypothesis by quantifying total F-FDG uptake in the bone marrow of patients with visibly enhanced bone marrow uptake and computing its effect on tumour SUV.

METHODS

Total F-FDG in bone marrow was measured in two groups of PET/CT studies: one (n=19) with visibly enhanced bone marrow, the other (n=5), a baseline group with 'normal' levels of uptake. To measure the F-FDG in bone marrow, the entire skeleton in the CT was segmented from surrounding tissue, and the resulting volume applied to the PET image. Using kinetic analysis we show that the predicted correction factor to tumour SUV is given by (1-q0/Q)/(1-q/Q), where Q is the injected dose, and q and q0 are enhanced and baseline bone marrow uptake (MBq).

RESULTS

The enhanced bone marrow uptake averaged 8.9+/-3.2% of injected dose (15.2% max) vs. 4.2+/-0.4% (4.6% max) at baseline. This resulted in a predicted artificial decrease in tumour SUV of up to 11.5% (4.9+/-4.3%, on average).

CONCLUSION

Enhanced bone marrow uptake is predicted to reduce tumour SUVs by as much as 11.5% in our patient group and is a potential confounding factor in using SUV for monitoring tumour response to therapy.

Investigating the Existence of Quantum Metabolic Values in Non-Hodgkin’s Lymphoma by 2-Deoxy-2-[F-18]fluoro-d-glucose Positron Emission Tomography

OBJECTIVES

To investigate the existence of quantum metabolic values in various subtypes of non-Hodgkin's lymphoma (NHL).

METHODS

Fifty-eight patients with newly diagnosed NHL and positron emission tomography (PET) performed within three months of biopsy were included. The standardized uptake value (SUV) from PET over the area of biopsy and serum glucose [Glc] were recorded. The group glucose sensitivity(G) for indolent and aggressive NHL was obtained by linear regression with ln(SUV) = G x ln[Glc] + C, where C is a constant for the group. Finally, the individual's glucose sensitivity (g) was obtained by g = {ln(SUV)-C}/ln[Glc], along with their means in various subtypes of NHL. To further investigate the influence of extreme [Glc] conditions, the SUVs corrected by the individually calculated g at various glucose levels, [Glc'] using SUV' =SUV x {[Glc']/[Glc]}(g), were compared to the original SUVs for both indolent and aggressive NHL.

RESULTS

The averaged g (=G) for aggressive was significant different from that for indolent NHL (-0.94 +/- 0.51 vs. +0.13 +/- 0.10, respectively, p < 0.00005). There were significant differences in SUV for [Glc] < 80 or >110 mg/dl for both types of NHL. Unlike overlap among SUVs between NHL subtypes, the g value clearly categorized them into two distinct groups with positive (near-zero) and negative g values (around -1) for the indolent and aggressive NHLs, respectively.

CONCLUSIONS

Distinct quantum metabolic values of -1 and 0 were noted in NHL. Aggressive NHL has a more negative value (or higher glucose sensitivity) than that of indolent and, thus, is more susceptible to extreme glucose variation.