Analysis of equivalent uniform dose (EUD) and conventional radiation treatment parameters after primary and re-irradiation of malignant glioma

Background: Re-irradiation is a reasonable second treatment option
for patients with recurrent malignant glioma (MG) after previous
radio(chemo) therapy. However, only limited data is available
allowing for a precise selection of patients suitable for
re-treatment in regard to safety and efficacy. Methods: Using the
department database, 58 patients with two courses of percutaneous
radiation were identified. Besides classical dose-volume histogram
(DVH) parameters equivalent uniform dose (EUD) values were
calculated for the tumor and organs at risk (OARs), retrospectively
analyzed and correlated to survival outcome parameters. Cumulative
EUD values were also calculated in all cases where previous OAR
DVHs were available. Results: Median follow-up was 265 days and no
relevant toxicity was observed after re-irradiation in our patient
cohort during follow-up. Time interval between first and second
irradiation was regularly above 6 months. As a conservative
estimation of the cumulative EUD to the OARs, the EUDs of first and
second irradiation were added. Median cumulative EUD to the optic
chiasm was 48.8 Gy (range, 2.5-76.5 Gy), 57.4 Gy (range, 2.7-75.3
Gy) to the brainstem, 20.9/22.1 Gy (range, 0.0-68.3 Gy) to the
right/left optic nerve and 73.8 Gy (range, 64.9-77.3 Gy) to the
brain. No correlation between treated volume and survival was seen.
Conclusions: This study provides retrospective estimates on
cumulative doses at the OARs. EUD values are derived and may serve
as reference for further studies, including planning studies where
specific constraints are needed.