gms | German Medical Science

Convection-enhanced drug delivery is a locoregional therapeutic approach currently used in several brain tumour studies. Usually, tumour progression is determined mainly using gadolinium enhanced T1 MRI imaging. In our current phase II paclitaxel study, we evaluated the use of O-(2-[¹⁸F]fluoroethyl)-L-tyrosine (FET) PET to determine the therapeutic effects of direct paclitaxel delivery.

Eight patients (6 males, 2 females, mean age: 53±10 yrs) with recurrent glioblastoma have currently been treated with CED of paclitaxel. It was infused over one or two catheters stereotactically placed into the recurrent tumour for 120 hours at a flow rate of 0.3 ml/h. FET-PET and MRI scans were performed before and four weeks after therapy followed by two months intervals to document follow-up. For quantitative evaluation of the PET results, the maximal SUV (SUV_max) of recurrent tumour was determined and the ratio to the background (BG) was calculated. The FET-PET data were correlated to MR imaging and clinical course.

Prior to treatment, all tumours showed pathologic Gd enhancement on MRI as well as high FET uptake (SUV_max/BG of 3.2±0.8). Four weeks after therapy, a statistically significant decrease of overall FET uptake was observed in all patients (SUV_max/BG: -17%; p<0.01). During the subsequent follow-up, no recurrence was detected within the CED area. Partial response (PR) was observed in 7/8 patients, stable disease in 1 patient. In 5 patients progression occurred distant from the CED area between 3 and 13 months after therapy. During the stable period of partial response, FET uptake initially remained constant but ultimately increased markedly in the area of tumour regrowth (+46%). All FET-PET changes clearly correlated with progression. In contrast, varying degrees of contrast enhancement in MRI could not reliably assess disease progression.

O-(2-[¹⁸F]fluoroethyl)-L-tyrosine PET is a more reliable tool than MRI to differentiate unspecific posttherapeutic changes from those induced by tumour regrowth after convection-enhanced paclitaxel delivery. Additionally, FET-PET supports the efficacy of this therapy by a statistically significant decrease of FET uptake and complete lack of tumour regrowth within the convection zone.