shows the averaged values of three metabolite ratios (i.e., NAA/norCre, Cho/norCre, and NAA/Cho) with standard deviations, the coefficients of variation, and p values tested by student t-statistics between two pre-treatment visits in three ROIs. Relatively small mean differences were observed between two baselines, with moderate but acceptable coefficients of variation (< 30%).
Mean and standard deviation of NAA/norCre, Cho/norCre, and NAA/Cho on day -5 and day -1 for all the patients; their coefficients of variance and p values between two baselines; in three ROIs.
demonstrates a representative example of serial T1 post-contrast MR images and raw spectra in one representative voxel (denoted by the blue-lined box) of the enhancing tumor region during the time-course of treatment. The spectra display dynamic changes of each metabolite's peak in the range of 0.5–4 ppm.
Figure 2 Serial T1 post-contrast MR images and raw spectra in one representative voxel (blue-lined box) of enhancing tumor region in the time course of treatment. The spectra exhibit the dynamic changes of each metabolite's peak in the range of 0.5 – 4 (more ...)
shows the changes in the NAA/norCre, Cho/norCre, NAA/Cho ratios relative to pretreatment values, as well as lipid and lactate levels normalized by norCre, averaging across all eligible patients.
Figure 3 Averaged MRS changes over all eligible patients relative to pretreatment values (%). a) NAA/Cho; b) (Lipids and Lactate)/norCre; c) NAA/norCre; d) Cho/norCre;; The number of the eligible patients at each time point is provided under each data point. Numerical (more ...)
The primary metabolic index in , NAA/Cho, provides a combined picture of the most commonly used diagnostic criterion of metabolic changes for some types of tumors (27
). Many studies have reported lower NAA/Cho ratio in tumors (compared to normal tissue) due to decreased levels of NAA and/or increased levels of Cho (36
); such findings are frequently interpreted as resulting from the replacement of normal brain tissue by cancerous tissue. Though averaged, NAA/Cho in both enhancing tumor and peritumor regions showed no significant change until 28 days; there was significant increase between days 28 and 56 (p=0.01), then a subsequent decrease. In the contralateral normal tissue, NAA/Cho was relatively constant.
As illustrated in , the ratio of lipids and lactate (including all lipid peaks in the range of 0.5-2 ppm) in enhancing tumor versus Cre on the contalateral normal side (norCre) decreased significantly on day 56. Like the other metabolites, (lipids and lactate)/norCre was relatively stable in the contralateral normal tissue.
show the individual behavior of the metabolites normalized by Cre in the contralateral tissue (norCre). illustrates a sharp increase in NAA/norCre in the enhancing tumor after a single dose of cediranib. The increase until day 56 (p=0.02), at which time point the value began to decrease until the end of the study (p=0.04). In the peritumoral region, NAA/norCre increased until day 28, and remained relatively constant close to the normal value (i.e., 1.5) until day 112 (p=0.04).
In contrast, Cho/norCre () in the enhancing tumor showed a different pattern: an increase up to day 28 (p=0.03), a decrease from 28-56 days, then no change until the end of the study (day 112). The decrease in Cho reached statistical significance (p=0.047) between days 28 and 56. A similar trend was found in the peritumoral region. In the contralateral normal tissue, both NAA/norCre and Cho/norCre remained relatively constant.
We also analyzed the changes in the MR parameters relative to baseline for the same subset of 20 patients; for reference, results are shown in Figure S1 (Supplementary Data)
The MRI data from the subset of patients from whom we also acquired analyzable MRS data were similar to the MRI findings of others in the whole 31-patient sample (16
). In both the larger data set of 31 patients and the subset of 20 patients from whom we acquired MRS data, the volume of contrast-enhanced tumor (CE-T1) decreased until day 28 and thereafter began to increase. An abrupt and substantial decrease in Ktrans
(mean ~ -70%) was noted immediately after the first dose of cedirinib (day 1). The relative tumor vessel size also decreased until day 28, and began to increase after day 28. We observed sustained decrease in vasogenic edema, demonstrated by reduced FLAIR lesion volumes, ADC, and Ve
for the duration of the therapy. These findings suggested a high probability of anti-permeability effects of cedranib until day 28.
We analyzed MRS/MRI findings in relation to patients' overall survival times, based on the six-month survival threshold. Early post-treatment time points (i.e., days 1, 28, 56) may be the most important for treatment management because early indications of therapeutic outcome provide better opportunity to optimize therapeutic intervention and improve survival (40
As shown in Figure S2 (Supplementary Data)
, the MRS data indicated no significant difference in the ratios of the metabolites, including NAA/norCre, Cho/norCre, NAA in tumor/NAA in the contralateral normal tissue (tumNAA/norNAA), and Cho in tumor/Cho in the contralateral normal tissue (tumCho/norCho); similarly, the group differences in MRI measurements of ‘high overall survival’ and ‘low overall survival’ responders were considered as having no significant effect. (Figure S3 in Supplementary Data
). However, NAA/Cho (), the most commonly used clinical MRS measure for discriminating normal and abnormal tissues (27
), notably showed an increase in the ‘high overall survival’ group (15%, 9%, 40% with p<0.05 on days 1, 28, and 56, respectively), while showing a decrease in the ‘low overall survival’ group (-12%, -10%, -20% on days 1, 28, and 56, respectively). Based on this finding, we performed ROC analysis to determine the probability that NAA/Cho predicts 6-month survival. In , the values of an area under the ROC curve (AUC) and p-values at early time points, particularly days 28 and 56, demonstrated the high possibilities (74% and 95%) and the significances (0.02 and 0.01).
the relative changes (%) in NAA/Cho separately grouped by the patients' overall survival (OS) periods based on six-month survival threshold at the early time points post-treatment (i.e days 1, 28, 56) in the enhancing tumor region.
Area Under the ROC curve on early time points (i.e. 1 day, 28 day, 56 day) to determine the prediction of NAA/Cho to 6-month survival
We compared the relative changes in the ratios of the three metabolites before and after one dose of cediranib to the changes in the absolute values of norCre and the T1 relaxation time constant in Figure S4 (Supplementary Data)
. The comparison showed subtle changes in norCre and T1 time constant after one dose, confirming that changes in NAA/norCre are independent of norCre and T1 changes.