1H-MRSI of radiation effects in normal-appearing white matter: dose-dependence and impact on automated spectral classification.

PURPOSE

To identify radiation-induced changes in healthy white-matter spectra in the first six months following radiotherapy, and assess the impact of these changes on an automated algorithm for detecting spectral abnormalities.

MATERIALS AND METHODS

1H-MRSI was performed on 10 patients with grade IV gliomas who were to undergo radiation therapy. Choline (Cho), creatine (Cr), and N-acetylaspartate (NAA) ratios were studied as a function of dose and time. The impact of these spectral changes on a spectral analysis algorithm was evaluated.

RESULTS

The Cho/NAA ratios rose to values of 0.66 +/- 0.15, 0.75 +/- 0.21, and 0.73 +/- 0.15 two months after therapy, compared to immediate post-therapy values of 0.56 +/- 0.15, 0.60 +/- 0.16, and 0.61 +/- 0.15 for the < 25, 25-50, and > 50 Gy dose groups, respectively. These maxima were followed by a dose-dependent recovery. A similar trend was found in the Cho/Cr ratio. The automated spectral analysis system incorporated the changing Cho/NAA ratio into a global redefinition of healthy tissue, but did not account for dose-dependent spatial variations in Cho/NAA ratios.

CONCLUSION

Radiation significantly alters the spectra of healthy tissues in the first six months after radiotherapy. This suggests that the radiation dose distribution should be considered during analysis of post-therapy spectra.