Interest of routine MR spectroscopic techniques for differential diagnosis between radionecrosis and progression of brain tumor lesions

The main objective of the study is to assess the feasibility and reproducibility of routine MRS to assist in the differential diagnosis between post-radiation necrosis and tumor progression. The secondary objective is to evaluate the accuracy of the method.

An additional sequence of MRS was added to the standard protocol routinely used for patient follow-up. To assess discomfort a control group was formed. The time required to perform MRS and analysis of results, and data about artefacts and technical limitations were collected. MRS results analyzed independently by two neuroradiologists were compared. The diagnostic accuracy of MRS was calculated using a composite reference standard.

The experimental group included 38 patients, the control group 41. The discomfort felt during the examination, is not significantly different between the groups. The average quality of SRM is rated as low. The frequency of cerebral radionecrosis is 13 % based on the reference standard used, 54 % and 46 % based on MRS results for the two observers. The additional time is 19,5 min. There is strong inter-observer agreement. The sensitivity and specificity of MRS are respectively for the diagnosis of radionecrosis of 60 % and 45 % (PPV = 16 %NPV = 87 %), for the diagnosis of tumor tissue of 25 % and 94 % (PPV = 80 %NPV = 57%).

MRS is probably not applicable in routine clinical practice; however, in view of our results and the literature, in selected cases, it could be a support in the diagnosis of radionecrosis or brain tumor progression. Radionecrosis is probably underestimated.