Diffusion magnetic resonance imaging as an evaluation of the response of brain metastases treated by stereotactic radiosurgery

BackgroundLoss of tumor cell results in a relative increase in extracellular space that may lead to alteration of ADC. Our purpose was to see if the ADC could be used, rather than methods depending on changes in tumor size, to predict treatment success after treatment of brain metastases with SRS.MethodsIn a prospective study, the ADCs of 21 patients with 32 solid or solid-dominated brain metastases were taken before and 1 week, 1 month, and at 3-month intervals after SRS. Mean ADC values at the various time intervals were compared with each other to see whether or not the ADC might be used as an early indicator of treatment success or failure.ResultsThe mean pretreatment value of the ADC in the metastatic tumors was 1.05 ± 0.12 × 10−3 mm2/s (mean ± SD). This value for the tumors rose significantly (P = .009) 7 days after SRS and continued to rise with time. Magnetic resonance imaging showed that 91% of these tumors had been controlled by the SRS. The ADC values in cystic/necrotic tumor tissue (2.13 ± 0.18 × 10−3 mm2/s) were significantly (P < .001) higher than those in noncentral necrotic tumor tissue (1.61 ± 0.14 × 10−3 mm2/s).ConclusionsThe ADC values might eventually be useful to evaluate treatment success—and in some patients, detected even at early time points—and to distinguish radiation-induced central necrosis from tumor regrowth in cases where other imagery is not definitive.