Long-term evaluation of the effect of hypofractionated high-energy proton treatment of benign meningiomas by means of 11C-L-methionine positron emission tomography

Purpose To determine if C-11-l-methionine PET is a useful tool in the evaluation of the long-term effect of proton beam treatment in patients with meningioma remnant. Methods Included in the study were 19 patients (4 men, 15 women) with intracranial meningioma remnants who received hypofractionated high-energy proton beam treatment. Patients were examined with C-11-l-methionine PET and MRI prior to treatment and after 6 months, and 1, 2, 3, 5, 7 and 10 years. Temporal changes in methionine uptake ratio, meningioma volume, meningioma regrowth and clinical symptoms throughout the follow-up period were evaluated. Results In 17 patients the tumour volume was unchanged throughout the follow-up. The methionine uptake ratio on PET decreased over the years in most patients. In two patients the tumour remnant showed progression on MRI. In these patients, prior to the volume increase on MRI, the methionine uptake ratio increased. One patient experienced transient clinical symptoms and showed radiological evidence of a radiation-induced reaction close to the irradiated field. Conclusion Proton beam treatment is a safe and effective treatment for achieving long-term growth arrest in meningioma remnants. Follow-up with C-11-l-methionine PET may be a valuable adjunct to, but not a replacement for, standard radiological follow-up.