Dynamic contrast-enhanced magnetic resonance imaging of osseous spine metastasis before and 1 hour after high-dose image-guided radiation therapy

Abstract

OBJECTIVE High-dose image-guided radiation therapy (HD IGRT) has been instrumental in mitigating some limitations of conventional RT. The recent emergence of dynamic contrast-enhanced (DCE) MRI to investigate tumor physiology can be used to verify the response of human tumors to HD IGRT. The purpose of this study was to evaluate the near-immediate effects of HD IGRT on spine metastases through the use of DCE MRI perfusion studies. METHODS Six patients with spine metastases from prostate, thyroid, and renal cell carcinoma who underwent HD IGRT were studied using DCE MRI prior to and 1 hour after HD IGRT. The DCE perfusion parameters plasma volume (V_p) and vascular permeability (K_trans) were measured to assess the near-immediate and long-term tumor response. A Mann-Whitney U-test was performed to compare significant changes (at p ≤ 0.05) in perfusion parameters before and after RT. RESULTS The authors observed a precipitous drop in V_p within 1 hour of HD IGRT, with a mean decrease of 65.2%. A significant difference was found between V_p values for before and 1 hour after RT (p ≤ 0.05). No significant change was seen in V_p (p = 0.31) and K_trans (p = 0.1) from 1 hour after RT to the first follow-up. CONCLUSIONS The data suggest that there is an immediate effect of HD IGRT on the vascularity of spine metastases, as demonstrated by a precipitous decrease in V_p. The DCE MRI studies can detect such changes within 1 hour after RT, and findings are concordant with existing animal models.

Keywords: AIF = arterial input function; ASMase = acid sphingomyelinase; DCE = dynamic contrast-enhanced; FA = flip angle; FOV = field of view; HD IGRT = high-dose image-guided radiation therapy; Ktrans = vascular permeability; ROI = region of interest; Vp = plasma volume; dynamic contrast-enhanced MRI; high-dose image-guided radiation therapy; spine tumor response.

FIG. 1

Sagittal T1-weighted MRI study illustrates the structural anatomy of the spine for all 6 patients prior to treatment with HD IGRT. The patient in Case 1 shows a metastatic lesion at L-4; the patient in Case 2 at L-2 (lesion A—lesion B not shown); the patient in Case 3 at T-5 (lesion A) and T-11 (lesion B); the patient in Case 4 at T-10; the patient in Case 5 at L-3; and the patient in Case 6 at L-4. The patient labeling is in concordance with Table 1.

FIG. 2

Sagittal T1-weighted DCE MRI perfusion maps for the parameters V_p and K_trans at times pre-RT, 1 hour post-RT, and subsequent follow-ups. The images were obtained in the patient in Case 6 and show the perfusion of spine metastasis to L-4 from renal cell carcinoma. The V_p decreased from 36.7 preoperatively to 1.85 at 1 hour post-RT (a 95% decrease). The K_trans map shows a similar decrease from 14 preoperatively to 4 at 1 hour post-RT (a 71.4% decrease). TX = treatment.

FIG. 3

A line plot illustrating the median V_p and K_trans at various times, including before RT, 1 hour after RT, and at different follow-up sessions. The bars and whiskers illustrate the range in V_p and K_trans values recorded from the patients’ T1-weighted DCE MRI scans. The V_p ranged from 4.1 to 50 before RT and from 0.78 to 18.3 at 1 hour after RT. The K_trans ranged from 1.7 to 14 before RT and from 1.35 to 4 at 1 hour after RT.

FIG. 4

Case 1. Sagittal T1-weighted structural image showing a new metastatic lesion in L-5 (arrow).

FIG. 5

Case 1. Sagittal T1-weighted DCE MRI perfusion maps for the parameters V_p and K_trans before RT, and at follow-up visits 3 and 5 after RT. Follow-up 3 illustrates a hypointensity at L-5, whereas follow-up 5 shows a hyperintensity with V_p values of 5.4 and K_trans of 1.86. The V_p color map is consistent with the clinical finding of new metastases to L-5. The arrows designate untreated L-4 metastasis prior to radiation therapy.