Purpose: Functional/metabolic information provided by MR-spectroscopy (MRSI) suggests MRI may not be a reliable indicator of active and microscopic disease in malignant brain tumors. We assessed the impact MRSI might have on the target volumes used for radiation therapy treatment planning for high-grade gliomas.
Methods and materials: Thirty-four patients (22 Grade III; 12 Grade IV astrocytomas) were evaluated; each had undergone MRI and MRSI studies before surgery. MRI data sets were contoured for T1 region of contrast enhancement (T1), region of necrosis, and T2 region of hyperintensity (T2). The three-dimensional MRSI peak parameters for choline (Cho) and N-acetylaspartate (NAA), acquired by a multivoxel technique, were categorized based on an abnormality index (AI), a quantitative assessment of tissue metabolite levels. The AI data were aligned to the MRI and displayed as three-dimensional contours. AI vs. T conjoint and disjoint volumes were compared.
Results: For both grades, although T2 estimated the region at risk of microscopic disease as being as much as 50% greater than by MRSI, metabolically active tumor still extended outside the T2 region in 88% of patients by as many as 28 mm. In addition, T1 suggested a lesser volume and different location of active disease compared to MRSI.
Conclusion: The use of MRSI to define target volumes for RT treatment planning would increase, and change the location of, the volume receiving a boost dose as well as reduce the volume receiving a standard dose. Incorporation of MRSI into the treatment-planning process may have the potential to improve control while reducing complications.