On expedient properties of common biological score functions for multi-modality, adaptive and 4D dose optimization

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.

Equivalence of Gyn GEC-ESTRO guidelines for image guided cervical brachytherapy with EUD-based dose prescription

Background

To establish a generalized equivalent uniform dose (gEUD) -based prescription method for Image Guided Brachytherapy (IGBT) that reproduces the Gyn GEC-ESTRO WG (GGE) prescription for cervix carcinoma patients on CT images with limited soft tissue resolution.

Methods

The equivalence of two IGBT planning approaches was investigated in 20 patients who received external beam radiotherapy (EBT) and 5 concomitant high dose rate IGBT treatments. The GGE planning strategy based on dose to the most exposed 2 cm³ (D2cc) was used to derive criteria for the gEUD-based planning of the bladder and rectum. The safety of gEUD constraints in terms of GGE criteria was tested by maximizing dose to the gEUD constraints for individual fractions.

Results

The gEUD constraints of 3.55 Gy for the rectum and 5.19 Gy for the bladder were derived. Rectum and bladder gEUD-maximized plans resulted in D2cc averages very similar to the initial GGE criteria. Average D2ccs and EUDs from the full treatment course were comparable for the two techniques within both sets of normal tissue constraints. The same was found for the tumor doses.

Conclusions

The derived gEUD criteria for normal organs result in GGE-equivalent IGBT treatment plans. The gEUD-based planning considers the entire dose distribution of organs in contrast to a single dose-volume-histogram point.