Feasibility study of finalizing the extended adjuvant temozolomide based on methionine positron emission tomography (Met-PET) findings in patients with glioblastoma

In the management of patients with newly diagnosed glioblastoma, there is no standard duration for adjuvant temozolomide treatment. This study aimed to assess the feasibility of finalizing adjuvant temozolomide treatment on the basis of methionine uptake in methionine positron emission tomography (Met-PET). We conducted a retrospective review of glioblastoma patients who underwent more than twelve cycles of temozolomide (extended temozolomide) treatment after resection and concomitant chemoradiotherapy with no evidence of recurrence on MRI. In addition to the methionine uptake value at the completion of extended temozolomide, local and distant recurrence and progression-free survival were also analyzed. Forty-four patients completed the extended temozolomide treatment. Among these, 18 experienced some type of tumor recurrence within one year. A Tmax/Nave value of 2.0 was the optimal cut-off value indicating progression. More than 80% of the patients with low methionine uptake completed the temozolomide treatment, and subsequent basic MRI observations showed no recurrence within one year after Met-PET. Subgroups with high uptake (≥2.0), even with continuation of temozolomide treatment, showed more frequent tumor progression than patients with low uptake (<2.0) who completed the extended temozolomide treatment (p < 0.001, odds ratio 14.7, 95% CI 3.46–62.3). The tumor recurrence rate increased in stepwise manner according to methionine uptake. Finalization of the extended temozolomide treatment on the basis of low uptake value was feasible with a low recurrence rate. Compared to MRI, Met-PET shows better ability to predict tumor progression in long-term glioblastoma survivors with extended temozolomide use.