Longitudinal MRI findings in patients with newly diagnosed glioblastoma after intraoperative radiotherapy.

BACKGROUND AND PURPOSE: Postradiation treatment effects (pseudoprogression/radionecrosis) may bias MRI-based tumor response evaluation. To understand these changes specifically after high doses of radiotherapy, we analyzed MRIs of patients enrolled in the INTRAGO study (NCT02104882), a phase I/II dose-escalation trial of intraoperative radiotherapy (20-40 Gy) in glioblastoma.

METHODS: INTRAGO patients were evaluated and compared to control patients who received standard therapy with focus on contrast enhancement patterns/volume, T2 lesion volume, and mean rCBV.

RESULTS: Overall, 11/15 (73.3%) INTRAGO patients (median age 60 years) were included. Distant failure was observed in 7/11 (63.6%) patients, local tumor recurrence in one patient (9.1%). On the first follow-up MRI all but one patient demonstrated enhancement of varying patterns around the resection cavity which were: in 2/11 (18.2%) patients thin and linear, in 7/11 (63.6%) combined linear and nodular, and in 1/11 (9.1%) voluminous, indistinct, and mesh-like. In the course of treatment, most patients developed the latter two patterns (8/11 [72.7%]). INTRAGO patients demonstrated more often combined linear and nodular and/or voluminous, indistinct, mesh-like components (8/11 [72.7%]) in comparison to control patients (3/12 [25%], p = 0.02). INTRAGO patients demonstrated significantly increasing enhancing lesion (p = 0.001) and T2 lesion volumes (p < 0.001) in the longitudinal nonparametric analysis in comparison to the control group. rCBV showed no significant differences between both groups.

CONCLUSIONS: High doses of radiotherapy to the tumor cavity result in more pronounced enhancement patterns/volumes and T2 lesion volumes. These results will be useful for the response evaluation of patients exposed to high doses of radiotherapy in future studies.