[F-DOPA PET/MR based target definiton in the 3D based radiotherapy treatment of glioblastoma multiforme patients....

Radiotherapy plays important role in the complex oncological treatment of glioblastoma multiforme (GBM). The modern 3D radiotherapy treatments are based on cross-sectional CT and MR information, however more attention is being paid to functional hybrid imaging describing the biological and functional morphology of tumor lesions. 18F-DOPA is an amino acid tracer with high specificity and sensitivity, which may play an important role in the precise definition of target volume in the irradiation process of GBM patients. Our study presents the first experiences with 18F-DOPA based PET/CT/MR 3D irradiation planning process.

In Hungary the 18F-DOPA radiotracer has been available for clinical use since September 2017. Between September 2017 and January 2018, at the Somogy County Kaposi Mór Teaching Hospital Dr. József Baka Diagnostic, Radiation Oncology, Research and Teaching Center 3 histologically verified glioblastoma multiforme patients received 18F-DOPA based 3D irradiation treatment. In the contouring process the native planning CT scanes were fused with the PET/MR series (T1 contrast enhanced, T2 and 18F-DOPA sequences). We defined 18F-DOPA uptake volume (BTV-F-DOPA), the T1 contrast enhanced MRI volume (GTV-T1CE), and the volume of the area covered by oedema on the T2 weighted MRI scan (CTV-oedema) in all patients. We also registered the BTV-F-DOPA volumes not covered by the conventional MR based target volumes.

Examining the 3 cases, the average volume of 18F-DOPA tumor was 22.7 cm3 (range 15.3-30.9; SD = 7.82). The average GTV T1 CE was found to be 8.7 cm3 (range 3.8-13.2; SD = 4.70). The mean CTV oedema volume was 40.3 cm3 (range 27.7-57.7; SD = 15.36). A non-overlapping target volume difference (BTV-F-DOPA not covered by CTV oedema area) was 4.5 cm3 (range 1-10.3; SD = 5.05) for PTV definition.

Based on our results the tumor area defined by the amino acid tracer is not fully identical with the MRI defined T2 oedema CTV. 18F-DOPA defined BTV can modify the definiton of the PTV, and the radiotherapy treatment.