Differentiating radiation effect from tumor progression after stereotactic radiosurgery: T1/T2 matching.

Radiosurgery is a common approach for patients with brain tumors. After stereotactic radiosurgery (SRS), the differentiation between tumor progression and radiation effects (RE) can be difficult using current clinical criteria supplemented by computed tomography (CT) or magnetic resonance (MR) imaging (MRI). This is one of the greatest challenges in radiosurgical practice and indeed in neurooncology. Metabolic imaging with single-photon emission computerized tomography (SPECT) or positron emission tomography (PET) also fails to provide reliable predictive information. We studied whether selected clinical and MRI criteria can reliably differentiate tumor progression from REs in patients who required resection of their brain mass. Differentiation between tumor progression and REs is a fundamental challenge that directly affects patient care. Desquesada et al recently reported that their novel radiographic feature, called the ‘‘lesion quotient,’’ which was the ratio of the nodule volume as seen on T2-weighted MR imaging to the total-enhancing area on T1-weighted MR imaging, was significantly associated with tumor recurrence or REs. We focused on the correlation of any nodular lesion margin (not the measured lesion volume) on T2-weighted MR imaging compared to T1-weighted enhanced imaging.