gms | German Medical Science

Objective: GBM is almost always recurring despite aggressive therapy. Complete removal of contrast enhancing tumor mass is a strong prognostic factor but adjuvant therapies such as radiochemotherapy are a decisive part of the treatment strategy to prolong the time to recurrence. Tumor recurrence occurs at the border of the resection cavity in over 90% of cases. Therefore, it might be helpful to be able to predict the location of tumor recurrence in the postoperative images to customize further treatment, i.e. a radiation boost to this area or a re-resection. FET-PET might be a helpful technique, for it is able to differentiate tumor tissue from normal brain with a high specificity as an adjunct to MRI.

Method: 34 consecutive cases of operations (complete and incomplete resections of contrast enhancing tumor) of a glioblastoma in 31 patients with complete imaging data of FET-PET and MRI pre-, postoperative and during follow-up were included in the analysis. Immediate postoperative and follow-up imaging data were evaluated. In the postoperative FET-PET the tumor-to-normal brain ratio (TTB) around the walls of the resection cavity was measured. Raised levels of the TTB were recorded and anatomically correlated to the site of later tumor recurrence via image fusion.

Results: In all eleven cases of incomplete tumor resection, recurrence expectedly occurred at the site of residual tumor. In 15 cases of complete resections according to MRI and PET criteria, FET uptake was elevated all around the resection cavity but with a clear hot spot at the site of later recurrence. Nevertheless, TTB was below 1.6, so the diagnosis of residual tumor was not made. In a single case, in two of three remaining hot spots (TTB<1.6) tumor recurrence was found. In two cases, parts of the recurrent tumor were found outside the FET-PET hot spots. In four cases, an only slightly raised TTB around the resection cavity was found without any hot spot. One case without any tracer uptake postoperatively is free of recurrence to date which is 28 months after initial resection. Thus, tumor recurrence was found in 27 out of 34 cases at a site of raised TTB in the postoperative FET-PET. Therefore, the location of tumor recurrence might have been predicted directly postoperatively by FET-PET.

Conclusions: Immediate postoperative FET-PET might be a helpful adjunct for planning adjuvant therapies as it might be possible to predict tumor recurrence by FET-PET. This conclusion must be endorsed by a higher volume study.