In vivo optical spectroscopy detects radiation damage in brain tissue

OBJECTIVE: Magnetic resonance imaging abnormalities in malignant brain tumors after irradiation may represent either recurrent tumor or radiation injury. Optical spectroscopy may represent a novel technique to identify radiation damage in brain tissues and to differentiate contrast-enhancing lesions from recurrent tumor. METHODS: Fluorescence and diffuse reflectance spectra were acquired from 90 patients: 15 undergoing surgical resection for presumed recurrent tumor after radiation therapy, 15 with epilepsy and hippocampal sclerosis, and 60 with tumors who had not received irradiation. Optical spectra were acquired from 6 to 10 sites and were compared with a biopsy obtained from beneath the optical spectroscopy probe; the data then were classified by a neuropathologist blinded to the spectroscopy data. A probe for the intraoperative collection of diffuse reflectance and fluorescence spectra was used. RESULTS: Thirteen of 15 patients (29 of 129 spectra) with previous irradiation showed a unique spectral feature characterized by a fluorescence peak centered at 500 nm (F-500). All biopsy specimens showing histopathological signs of radiation injury had the F-500 on their corresponding spectra (18 of 18). The 17,00 was identified in another 10% (11 of 111 spectra) of samples with previous irradiation but no histologically identifiable signs of radiation damage. The F-500 was never seen in the normal temporal lobe of epilepsy patients with hippocampal sclerosis (0 of 105) and was seen in only 1.5% of tumor patients who did not undergo previous irradiation (6 of 433). CONCLUSION: Optical spectroscopy detects radiation damage in brain tissues. The F-500 spectral peak may allow accurate selection of tissues for biopsy in evaluating patients with new, contrast-enhancing lesions in the setting of previous irradiation.