Dynamic 11C-Methionine PET-CT: Prognostic Factors for Disease Progression and Survival in Patients with Suspected Glioma Recurrence

Simple Summary

Recurrence after initial treatments is an expected event in glioma patients, particularly for high-grade glioma, with a median progression-free survival of 8–11 weeks. The prognostic evaluation of disease is a crucial step in the planning of therapeutic strategies, in both the primary and recurrence stages of disease. The aim of our retrospective study was to assess the prognostic value of ¹¹C-methionine PET-CT dynamic and semiquantitative parameters in patients with suspected glioma recurrence at MR, in terms of progression-free survival and overall survival. In a population of sixty-seven consecutive patients, both static and kinetic analyses provided parameters (i.e., tumour-to-background ratio and SUVmax associated with time-to-peak, respectively) able to predict both progression-free and overall survival in the whole population and in the high-grade glioma subgroup of patients. Dynamic ¹¹C-methionine PET-CT can be a useful diagnostic tool, in patients with suspicion of glioma recurrence, able to produce significant prognostic indices.

Abstract

Purpose: The prognostic evaluation of glioma recurrence patients is important in the therapeutic management. We investigated the prognostic value of ¹¹C-methionine PET-CT (MET-PET) dynamic and semiquantitative parameters in patients with suspected glioma recurrence. Methods: Sixty-seven consecutive patients who underwent MET-PET for suspected glioma recurrence at MR were retrospectively included. Twenty-one patients underwent static MET-PET; 46/67 underwent dynamic MET-PET. In all patients, SUVmax, SUVmean and tumour-to-background ratio (T/B) were calculated. From dynamic acquisition, the shape and slope of time-activity curves, time-to-peak and its SUVmax (SUVmax_TTP) were extrapolated. The prognostic value of PET parameters on progression-free (PFS) and overall survival (OS) was evaluated using Kaplan–Meier survival estimates and Cox regression. Results: The overall median follow-up was 19 months from MET-PET. Recurrence patients (38/67) had higher SUVmax (p = 0.001), SUVmean (p = 0.002) and T/B (p < 0.001); deceased patients (16/67) showed higher SUVmax (p = 0.03), SUVmean (p = 0.03) and T/B (p = 0.006). All static parameters were associated with PFS (all p < 0.001); T/B was associated with OS (p = 0.031). Regarding kinetic analyses, recurrence (27/46) and deceased (14/46) patients had higher SUVmax_TTP (p = 0.02, p = 0.01, respectively). SUVmax_TTP was the only dynamic parameter associated with PFS (p = 0.02) and OS (p = 0.006). At univariate analysis, SUVmax, SUVmean, T/B and SUVmax_TTP were predictive for PFS (all p < 0.05); SUVmax_TTP was predictive for OS (p = 0.02). At multivariate analysis, SUVmax_TTP remained significant for PFS (p = 0.03). Conclusion: Semiquantitative parameters and SUVmax_TTP were associated with clinical outcomes in patients with suspected glioma recurrence. Dynamic PET-CT acquisition, with static and kinetic parameters, can be a valuable non-invasive prognostic marker, identifying patients with worse prognosis who require personalised therapy.

Positron Emission Tomography with 11C-Methionine and Computed Tomography of Intracranial Tumours Compared with Histopathologic Examination of Multiple Biopsies

A selected group of 36 patients with suspected supratentorial gliomas were investigated with positron emission tomography (PET) using 11C-methionine and transmission computed tomography (CT) before and after intravenous injection of contrast medium. Every examination was performed with the head fixed in a plastic helmet and a baseplate to guarantee that the slice orientation was the same at examinations with the two modalities and over time. Guided by the examinations, multiple stereotactic biopsies were performed with the biopsy instrument mounted on the baseplate. Regional accumulation of methionine was compared with histology of the corresponding samples and with attenuation before and after injection of contrast medium as well as mass effect on CT. Typically, there was a low attenuating lesion with a slight mass effect on CT. There was an increased accumulation compared with normal brain tissue in 31 cases of tumours and ordinary or decreased accumulation in 3 cases of tumours. In 22 cases with increased accumulation of methionine the extension of the tumour judged by PET corresponded with that of histology. In 4 cases tumour cells were found outside the area with pathologic methionine uptake. In 5 patients there were areas with increased methionine accumulation where no tumour cells were found. In 22 cases PET using methionine was more accurate than CT in defining the tumour boundaries as determined from the histologic findings. Four groups of biopsy specimens with different amounts of methionine accumulation are described. The uptake in a single biopsy gives good but not exact information about the histology of the specimen.

The sequential changes in DNA synthesis, glucose utilization, protein synthesis, and peripheral benzodiazepine receptor density in C6 brain tumors after chemotherapy to predict the response of tumors to chemotherapy

BACKGROUND

Monitoring therapy in patients with brain tumors is very difficult and unreliable. It has been shown that there is no good correlation between tumor sensitivity measured in vitro and in situ tumor response to therapies.

METHODS

Sequential changes in tumor size, number of DNA synthesizing cells (labelling index [LI]), glucose utilization (LCGU), protein synthesis (LCPS), and peripheral benzodiazepine receptor (PBR) density were examined after chemotherapy for seven days. This was done using antibromodeoxyuridine immunohistochemical stain and multiple tracer quantitative autoradiography in a C6 rat brain with an implanted glioma. On Day 10 after inoculation, the rats were divided into 5 experimental groups: (1) a nontreatment group (control Group 1); (2) a group received 5% dextrose intraarterial (IA) administration (control Group 2); (3) a group received 1,3-bis-(2-chloroethyl) nitrosourea (BCNU) intravenous (i.v.) administration (Group 3) (5% dextrose was solvent); (4) a group received BCNU IA administration (Group 4) (5% dextrose was solvent); and (5) a group received sarcosinamide chloroethyl nitrosourea (SarCNU) IA administration (Group 5) (solvent as for the BCNU group).

RESULTS

Three treatments showed a significant decrease (P < 0.003) in tumor growth. The most effective treatment was BCNU IA and SarCNU IA was moderately effective. BCNU i.v. showed no effect on tumor growth when compared with the two control groups. The change in the peak LI correlated well with the peak LCGU. These parameters decreased markedly and significantly in both Group 4 and Group 5 from Day 1 after treatment. The rates of the decrease in these biologic factors also correlated well with a decrease in the tumor growth. The LCPS did not correlate with a decrease in the LI or LCGU. The dissociation constant (Kd) and densities of the receptors PBR (B max) did not change significantly in any of the treatment groups during the observation period.

CONCLUSIONS

From the results presented, we concluded that changes in the LI and LCGU represent the most reliable parameters with which to predict the response or sensitivity of this glial tumor to the treatments applied. These data suggest that if changes in peak LCGU were measured in tumors using positron emission tomography, they might be instrumental in providing in vivo information about the sensitivity of a tumor to a given treatment without the need for repeated tumor biopsy.

Calcified astrocytoma of the amygdalo-hippocampal region in children

Three pediatric cases of temporal lobe seizure due to calcified glioma of amygdalo-hippocampal region are described. Computed tomography and magnetic resonance imaging showed dense calcification with no postcontrast enhancement in the amygdalo-hippocampal region. Positron emission tomography showed low oxygen metabolism, low glucose metabolism, hypermetabolism of amino acids, and low regional cerebral blood flow in the tumors. Single photon emission computed tomography showed a high accumulation of 201Tl chloride and 123I-isopropyl iodoamphetamine in one tumor, but otherwise low radioisotope uptake. These studies indicated low-grade malignancies. The patients were treated by partial tumor removal and radiotherapy. Histological examination of the tumor specimens showed astrocytoma with interstitial calcification. One patient died due to tumor recurrence, while the others are doing well with minimal seizure. We recommended temporal lobectomy in similar cases to achieve complete remission.

PET: brain tumor biochemistry

Most mechanisms of drugs which are used in brain tumor chemotherapy are well characterized: alkylation of DNA components (nitrosoureas), binding with tubulin protein resulting in metaphase arrest (vincristine), chromatid breaks and chromosome translocations (procarbazine), or inhibition of ribonucleotide reductase (hydroxyurea) [1]. These drugs exert their effects mainly during certain cell cycle phases of proliferating cells, particularly when DNA is synthesized. From this it can be assumed that the efficacy of these drugs depends on the fraction of proliferating cells. Thus it would be of great importance to estimate the proliferation rate of brain tumors which could guide chemotherapy in individual patients. Positron emission tomography (PET) measures quantitatively the in vivo tissue uptake of tracer substances. In tumors, the uptake appears to be altered in a characteristic way determined by biochemical properties of tumor tissue. Some aspects of brain tumor metabolism which are theoretically related to proliferation have been investigated with PET. In the following, the literature is reviewed with regard to: 1) tracer substances whose uptake has been thought to reflect tumor malignancy (11C-methionine, 18F-fluoro-deoxyglucose), and 2) tracers which theoretically could reflect mechanisms specifically related to DNA synthesis (11C-putrescine, ligands for peripheral benzodiazepine receptors).

Effects of vasopressin on blood-brain transfer of methionine in dogs

We used a simplified probe detection system for positron-emitting radionuclides in order to measure blood-brain barrier transport of amino acids in anesthetized dogs. Plasma and brain time-activity curves were recorded after intravenous bolus injection of L-[11C]methionine before and after administration of 1 microgram of vasopressin. Three-compartment models with three or four transfer coefficients were used to derive the kinetics of L-[11C]methionine uptake in brain. The blood-brain clearance of the tracer (K1) was 0.075 ml ml-1 min-1 before and 0.041 ml ml-1 min-1 after injection of vasopressin. The partition volume and the initial distribution (plasma) volume of methionine were unchanged and within the expected limits. The net accumulation rate of methionine (K), estimated by both the four-parameter (kinetic) and three-parameter (graphic) approaches, decreased after vasopressin injection in all six studies.

Regional cerebral L-[14C-methyl]methionine incorporation into proteins: evidence for methionine recycling in the rat brain

The specific activity (SA) of free methionine was measured in plasma and in different regions of the rat brain at 15, 30, or 60 min after intravenous infusion of L-[14C-methyl]methionine. Within these time periods, an apparent steady state of labeled free methionine in plasma and in brain was reached. However, the brain-to-plasma free methionine SA ratio was found to be approximately 0.5, showing that an isotopic equilibrium between brain and plasma was not attained. This suggests the presence of an endogenous source of brain free methionine (likely originating from protein breakdown), in addition to the plasma source. The contribution of this endogenous source to the content of free methionine varies significantly among the different brain regions. Our results indicate that the regional rates of protein synthesis measured with L-[11C-methyl]methionine using positron emission tomography would be underestimated, since the local fraction of brain methionine derived from protein degradation would not be considered.

Measurement of free intracellular and transfer RNA amino acid specific activity and protein synthesis in rat brain in vivo

Brain protein synthesis was measured in anesthetized adult, male Sprague-Dawley rats by an in situ internal carotid arterial perfusion technique using [3H]leucine. The specific activity of free intracellular leucine and of tRNA leucine were determined by HPLC separation of phenylisothiocyanate (PITC) derivatives of amino acids. The specific activity of the leucyl-tRNA pool rapidly equilibrated with the free intracellular leucine pool within 2 min. The specific activity of the tRNA and free leucine pools in brain reached equilibrium by 10 min. Plasma amino acid specific activity, however, remained threefold higher than the specific activity of tRNA and free leucine pools. Estimates of protein synthesis were 0.62 +/- 0.06 nmol/min/g and were constant between 10 and 30 min of perfusion. The in situ perfusion model for protein synthesis described is a controlled system suited to measurements of protein synthesis in brain that can be applied to the study of brain metabolism under changing physiological conditions.