FET PET to differentiate between post-treatment changes and recurrence in high-grade gliomas: a single center multidisciplinary clinic controlled study

Abstract

Purpose: The clinico-radiological dilemma in post-treatment high-grade gliomas, between disease recurrence (TR) and treatment-related changes (TRC), still persists. FET (Fluoro-ethyl-tyrosine) PET has been extensively used as problem-solving modality for cases where MR imaging is inconclusive. We incorporated a systematic imaging and clinical follow-up algorithm in a multi-disciplinary clinic (MDC) setting to analyse our cohort of FET PET in post-treatment gliomas.

Methods: We retrospectively analyzed 171 patients of post-treatment grade III and IV glioma with equivocal findings on MRI. 185-222 MBq of 18 F-FET was injected and dedicated static imaging of brain was performed at 20 min. TBR (Tumor to background ratio) was used as semi-quantitative parameter. Cutoff of 2.5 was used for image interpretation. Imaging findings were confirmed with histopathological diagnosis, wherever available or in a multidisciplinary joint clinic based on serial imaging.

Results: 121 of 171 patients showed recurrent disease on FET PET, on follow up, 109 were confirmed with recurrence; 7 patients showed TRC, whereas 5 were treated with bevacizumab, with no further clinico-radiological deterioration, thus confirming TRC. 50 patients showed TRC on FET PET, on follow up on follow up, 40 were confirmed as true-negative. 10 patients who showed TBR less than 2.5 had confirmed TR on subsequent MR imaging. The overall sensitivity and specificity was 91.6 and 76.9% respectively, with a diagnostic accuracy of 87.13%.

Conclusion: There is potential for FET PET to be used along with MRI in the post treatment algorithm of high-grade glial tumors.

Keywords: FET PET; High grade glioma; MRI; Post-treatment changes; Recurrence.

Fig. 1

Disease recurrence on FET PET. 52-year-old male, case of anaplastic astrocytoma, post excision, received adjuvant radiotherapy along with temozolomide (TMZ), followed by 12# maintenance TMZ, had a disease-free interval of 14 months. T2-weighted axial image (A-arrow) on follow-up MRI showed iso-to-hypointense areas in left frontal region, seen as swiss-cheese pattern of enhancement on axial post-contrast T1-weighted image (B-arrow). Patient underwent FET PET for characterisation of lesion, which showed high T-Wm ratio of 3.6 suggestive of disease recurrence. Focal areas of hyperperfusion were seen (D-arrow). Since patient was well-preserved clinically, he was followed up after 3 months with MRI, which showed increase in extent of infiltration on T2-weighted (E- arrow) and post-contrast-T1 weighted image (F- arrow). MDC discussions corroborated the FET and follow up MR findings and concluded that patient had unequivocal disease recurrence and was started on salvage treatment

Fig. 2

Post-treatment changes on FET PET. 39-year-old female, case of right parietal glioblastoma (GBM), post surgery, followed by concurrent radiotherapy-temozolomide (TMZ) and adjuvant TMZ, presented with left sided weakness, increased drowsiness. MR showed new onset T2 iso-to-hyperintense necrotic right periventricular lesion with post contrast irregular enhancement, and hyperperfusion in right temporoparietal region; FET PET showed low grade rim of tracer uptake in lesion (A - arrow), with tumor-to-white mater ratio of 1.8, suggestive of post-treatment changes. Fusion of PET and MR showed uptake corresponding to the rim of gliosis and enhancement on T2 (B - arrow) and T1-post contrast images (C - arrow). Patient was started on Bevacizumab following which improved symptomatically

Fig. 3

Receiver Operating Characteristics (ROC) curve for generating cut-off value for tumor-to-white mater ratio