High Diffusion-Weighted MRI Helpful in Brain Tumors

Laurie Barclay, MD

April 07, 2003

April 7, 2003 — High diffusion-weighted magnetic resonance imaging (HDWMRI) obtained before treatment may predict response to radiotherapy for patients with brain tumors, according an abstract published in the March 2003 issue of the Proceedings of the American Association for Cancer Research (AACR), a supplement to the journal Cancer Research. The data were intended to be presented at the AACR annual meeting in Toronto this week, but the meeting was cancelled because of the severe acute respiratory syndrome epidemic in that city.

"Diffusion-weighted MRI (DWMRI) can distinguish solid viable tumor from cystic and necrotic regions," write Yael Mardor, from the Sheba Medical Center in Ramat-Gan, Israel, and colleagues. "Our previous studies demonstrated that HDWMRI, which is more sensitive to the slow water population than conventional DWMRI, is more susceptible to detect early changes in human brain tumors post therapy than conventional DWMRI."

Of eight patients with nine brain lesions, four had grade III-IV gliomas and four had brain metastases, including three from breast and one from prostate cancer. All patients received conventional fractionated radiation therapy, consisting of fractions of 2 Gy per day to a total of 54-60 Gy in the patients with glioma, and fractions of 2 to 3 Gy per day to a total of 30 to 40 Gy in the patients with metastases.

The investigators calculated a diffusion index, R, reflecting tissue viability based on the water molecular diffusion, from diffusion-weighted images. Changes in tumor volumes on contrast-enhanced T1-weighted MRI, acquired before and 50 days on average after initiation of therapy, determined response to radiation therapy.

Before treatment, R correlated significantly with later tumor response or lack of response (r2 = 0.51; P < .03). The authors suggest that tumors with high viability, reflected in low pretreatment R values, respond better to radiation therapy than do tumors with high pretreatment R values, indicating necrosis.

"The correlation between the pre-treatment diffusion index and later tumor response indicates that HDWMRI may be used prior to initiation of treatment, to predict the outcome of certain anti-tumor therapies, thus enabling individual optimization of treatment plan," they write. "We are currently widening our investigations to include chemotherapy for primary CNS lymphomas and single fraction radiosurgery in brain tumor patients."

Proceedings of the American Association for Cancer Research. 2003;41:Abstract 2547

Reviewed by Gary D. Vogin, MD

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