Serial Proton MR Spectroscopic Imaging of Recurrent Malignant Gliomas after Gamma Knife Radiosurgery
Edward E. Gravesa,
Sarah J. Nelsona,
Daniel B. Vignerona,
Lynn Verheya,
Michael McDermotta,
David Larsona,
Susan Changa,
Michael D. Pradosa and
William P. Dillona
a From the Departments of Radiology (E.E.G., S.J.N., D.B.V., W.P.D.), Radiation Oncology (L.V., D.L.), and Neurological Surgery (M.McD., S.C., M.D.P.), University of California, San Francisco.
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FIG 1. Patient 7.
A–D, Serial contrast-enhanced gradient-echo images (2/6/1) and PRESS spectra (1000/144/1; voxel resolution, 1.0 cm3) acquired 1 day (A), 3 months (B), 5 months (C), and 6 months (D) after gamma knife treatment and aligned retrospectively. The 15-Gy isodose line is shown in red. The volume of contrast enhancement is significantly reduced at the 3-month time point, but increases at both the 5- and 6-month follow-ups. Reduction of Cho from baseline levels is apparent at the 3-, 5-, and 6-month time points. No significant change in NAA levels is observed, while a lactate/lipid resonance develops at 3 to 5 months but is reduced at 6 months. This patient received no further treatment and died 17 months after undergoing gamma knife radiosurgery.
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FIG 2. Patient 11.
A–C, Serial contrast-enhanced gradient echo-images (26/6/1) and PRESS spectra (1000/144/1; voxel resolution, 1.0 cm3) over the gamma knife target 3 days before (A) and 1 month (B) and 4 months (C) after radiosurgery. Two representative voxels are depicted, with the 15-Gy isodose line shown in red. The anterior voxel received an average radiation dose of 19.0 Gy, while the posterior voxel received 10.3 Gy. Reductions in both Cho and NAA as well as an increase in lactate/lipid are noted 1 month after radiosurgery. At 4 months, the less-irradiated voxel has developed a distinct tumorlike spectral pattern, while the heavily irradiated voxel appears necrotic. The lesion was resected, and brachytherapy seeds were implanted shortly after the last examination shown, but no biopsy samples were taken. The patient died 13 months after undergoing gamma knife treatment.
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FIG 3. Patient 4.
A–D, Serial contrast-enhanced gradient-echo images (26/6/1) and PRESS spectra (1000/144/1; voxel resolution, 1.0 cm3) of a cerebellar lesion 1 day before (A) and 3 months (B), 6 months (C), and 8 months (D) after treatment. The most irradiated voxel (almost completely within the red 15-Gy isodose line) received an average dose of 18.0 Gy, while the other three voxels received less than 10 Gy. At the time of radiosurgery low metabolite levels were noted in all voxels. Three months later, metabolite levels had increased, particularly within the radiation target. An increase in Cho is noted posterior to the radiation target at 3 and 6 months after treatment. At 8 months, these spectral abnormalities have become apparent radiologically, while the radiation target shows a necrotic spectrum. The development of a lactate/lipid peak within the high-dose region is also apparent from these serial observations. This patient was treated with gamma knife radiosurgery for a recurrence in the left superior frontal lobe 6 months after the initial treatment, and died 6 months thereafter.
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FIG 4. Patient 16.
A and B, Surface-coil contrast-enhanced gradient-echo images (26/6/1) and PRESS spectra (1000/144/1; voxel resolution, 0.34 cm3) acquired 2 weeks before (A) and 1 month after (B) gamma knife radiosurgery and aligned retrospectively. Before radiosurgery, several voxels with Cho above that of normal-appearing tissue are present beyond the 15-Gy isodose line (shown in red) of the prescribed treatment plan. One month later, the Cho/NAA ratio in eight of the nine voxels shown has increased to greater than 1. Also conspicuous are the strong lactate/lipid resonances after treatment. One month after the last examination shown here, the patient underwent resection. Histologic analysis of biopsy samples taken during surgery showed residual/recurrent anaplastic astrocytoma.
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FIG 5. Patient 18.
A–C, Contrast-enhanced gradient-echo images (26/6/1) and PRESS spectra (1000/144/1; voxel resolution, 1.0 cm3) acquired 1 day before (A) and 2 months (B) and 4 months (C) after radiosurgery. Voxel shifting was used to obtain a spectrum centered within the 15-Gy isodose line (shown in red). Although a hemorrhage present at the time of gamma knife treatment complicated radiologic interpretation, elevated Cho was clearly well outside the gamma knife target. At the last measured time point, the Cho/NAA ratio of the treated voxel (average dose, 18.5 Gy) was reduced to values comparable to normal tissue, while tumorlike spectral patterns remained present posteriorly. Resection was recommended at this time, during which biopsy samples were obtained that verified the new contrast enhancement as residual/recurrent GBM, including some necrosis.
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FIG 6. Patient 13.
A and B, Contrast-enhanced gradient-echo images (26/6/1) and spectra (1000/144/1; voxel resolution, 1.0 cm3) acquired the day of radiosurgery (A) and 5 months afterward (B). The radiation target was prescribed to include spectral abnormalities beyond the regions of contrast enhancement. Despite the enlarged treatment field, the 6-month time point shows a large increase in contrast-enhancing volume. Increases in Cho within regions of new contrast enhancement suggest they correspond to recurrent tumor. Also conspicuous is the development of lactate/lipid resonances within the high-dose region. Resection was performed after the final time point shown, which histologically confirmed the increased contrast enhancement as recurrent tumor.
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