Temporal lobe changes following radiation therapy: imaging and proton MR spectroscopic findings

Abstract

Radiation therapy for nasopharyngeal carcinoma affects the temporal lobes. This paper characterizes proton MR spectroscopic findings of the temporal lobes and correlates them with imaging changes. Single-voxel proton MR spectroscopic examinations were acquired from 13 healthy adult volunteers (25 spectra) and 18 patients (28 spectra). All patients had biopsy-confirmed nasopharyngeal carcinoma and were previously treated with radiation therapy. Six patients (33%) had a single treatment and 12 (67%) patients had two treatments. Point resolved spectroscopy (PRESS) method was used (TR = 3,000 ms, TE = 135 ms) and data processed automatically using the LCModel software package for metabolite quantification. Voxel size and geometry were adapted to the lesion to reduce skull-base lipid contamination. The metabolites were quantitated relative to water signal. For each location, an additional non-water-suppressed reference scan in fully relaxed conditions was performed. The imaging findings were divided into four categories: I, normal; II, edema only; III, contrast-enhancing lesions; and IV, cystic encephalomalacia. The N-acetyl-aspartate levels were reduced in 27 (96%) spectra. Choline was increased in 3 (11%), normal in 4 (14%), and reduced in 21 (75%) spectra. The creatine level was normal in 8 (29%) spectra and reduced in 20 (71%) spectra. Imaging showed 4 (14%) spectra with category-I imaging findings; 5 (18%) spectra with category-II findings; 15 (54%) spectra with category-III findings; and 4 (14%) spectra with category-IV findings. Magnetic resonance spectroscopy showed reduced N-acetyl-aspartate in radiation-induced temporal lobe changes. Creatine levels were relatively more stable. Choline levels may be increased, normal, or reduced. Imaging findings ranged from normal to contrast-enhancing lesions and cystic encephalomalacia.

MR Spectroscopy in Radiation Injury

“…Specific spectroscopic changes that occur in radiation necrosis have been reported and include slight depression of NAA and variable changes in Cho and Cr. [47][48][49][50] In addition, radiation necrosis may show a broad peak between 0 and 2 ppm, probably reflecting cellular debris containing fatty acids, lactate (Lac), and amino acids. 51 Also, other metabolites have been suggested to be present in radiation necrosis.…”

“…[41][42][43]47,48,50,51,59 Measurements of Metabolites and Ratio Calculations One of the major problems when reviewing the literature and comparing existing MR spectroscopy data is the use of various ways of calculating metabolite ratios. Several different methods have been used when trying to differentiate recurrent tumor from radiation-induced injury, and there is currently no consensus in the literature on which type of differently calculated ratios can best differentiate tumor recurrence from radiation change.…”

Quantitative/Objective Analyses of RT-Induced Late Normal Tissue Injury Using Functional Imaging

“…Late fibrotic injury usually evolves and becomes clinically manifested C6 months post-RT, and is characterized by progressive dyspnea, radiologic findings, and possible mortality (Theuws et al 1998;Goethals et al 2003). For patients treated for lung cancer, *5-35 % will develop symptomatic lung injury, and 50-100 % develop radiologic evidence of lung injury (the majority of which are asymptomatic) (Anscher et al 2003;Marks 1994;Graham et al 1999;Marks et al 2000;Fan et al 2001;Fu et al 2001). Similarly, for patients treated for breast cancer, 0-34 % may develop symptomatic lung injury, and 0-63 % of patients may develop radiologic changes (Dorr et al 2005;Cazzaniga et al 1998;Kuhnt et al 1998;Rotstein et al 1990;Schratter-Sehn et al 1993;Lind et al 2006b).…”

MR imaging of late radiation therapy- and chemotherapy-induced injury: a pictorial essay

“…In some cases of radiation necrosis, choline may be increased due to inflammation, demyelination, and gliosis ( Fig. 1e-I) [41,48], and so may resemble MR spectroscopic features of tumors. Subsequently, decreasing levels of Cho become evident, which reflects a dilution effect of decreased cell density and edema (Fig.…”

“…MR spectroscopic findings in radiationinduced changes range from cases with only a mild decrease in N-acetylaspartate (NAA) to very low or undetectable levels of all metabolites [41]. The earliest manifestation of radiation injury appears to be a decrease in NAA, which may be evident before changes in choline (Cho) or creatine (Cr).…”