† People involved in the organization of the challenge. ‡ People contributing data from their institutions.§ Equal senior authors.

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 (Vp) and vascular permeability (Ktrans) 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 Vp within 1 hour of HD IGRT, with a mean decrease of 65.2%. A significant difference was found between Vp values for before and 1 hour after RT (p ≤ 0.05). No significant change was seen in Vp (p = 0.31) and Ktrans (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 Vp. The DCE MRI studies can detect such changes within 1 hour after RT, and findings are concordant with existing animal models.

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Study Design Total of 40 patients with spinal metastases from renal cell carcinomas (RCC) or prostate carcinomas (PC) were studied using DCE (Dynamic contrast-enhanced) MRI. Objective Our aim was to evaluate spinal metastases from RCC and PC to assess the sensitivity and specificity of perfusion parameters obtained by quantitative and semi-quantitative methods, which would allow for noninvasive discrimination between hypovascular and hypervascular lesions. Summary of Background Data Conventional MRI can be inconclusive in assessing diagnostically complex spinal lesions in cancer patients in whom fibrosis, infarction, edema related to compression fractures, and infection may simulate malignant neoplasm. Conventional MRI is also of limited value in assessing tumor vascularity and identifying hypervascular tumors. DCE MRI offers an advantage over conventional MRI in that it provides anatomical, physiological, and hemodynamic information about neoplastic lesions. Methods DCE perfusion parameters: vascular permeability (Ktrans), plasma volume (Vp), wash-in slope, and peak-enhancement were measured to assess their potential as discriminators of tumor vascularity. A Mann-Whitney test (at p≤0.01), was performed to quantify and compare significance of perfusion parameters between the two groups. Results Of the four perfusion parameters studied, Vp was observed to have the largest difference in mean (µ) between PC (µ=3.29/sec) and RCC metastases (µ=5.92/sec). This was followed by the peak-enhancement, Ktrans, and wash-in parameters. A Mann-Whitney test showed a significant difference between Vp values for PC and RCC lesions (p≤0.001). Similarly, peak-enhancement showed a significant difference between the two histologies (p≤0.001), as did Ktrans (p≤0.01). The receiver operating characteristic curve showed that Vp recorded the highest area under the curve (0.867). Conclusion Vp was shown to be the best discriminator between spinal metastases from PC and RCC with the mean Vp of RCC metastasis being 1.8 times that of the PC lesions, thus discriminating between hyper- and hypovascular metastases, which has important clinical implications.

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