Influence of Homogeneous Dose Distribution Inside the Cancer Target on Local Control in Glioblastomas

Abstract

Purpose: Assessment of the effect of homogeneous distribution inside the radiation target on local control in glioblastoma.
 Material and methods: In patients under the age of 50, fractionation with the prescribed dose of 2 and 3 Gy was alternately used: the first patient was prescribed a regimen with a dose of 3 Gy, the next – with a dose of 2 Gy (a study involving a pairwise selection strategy). The same approach is used for the older age group (50 years and more). A total of 141 patients had morphologically confirmed glioblastoma (grade 4). 10 patients who had not completed a full course of radiation therapy were excluded. Additionally, 27 patients with GBM were added, treated in the experimental study of National Medical Research Radiological Centre without methodological features. In total, 158 patients were included in the study. 74 patients were treated with the prescribed dose of 2 Gy, 84 had a dose of 3 Gy.
 Results: The median homogeneity index in our study was 7.5 (95% Cl: 6,7-8,3). The minimum HI indicator was at the level of 2.5, the maximum – 36.9. We managed to identify the most informative level of the homogeneity index according to the criterion of local control. The median disease-free survival in the group with HI>=8.5 was 7.9 months (n=62; 95 % Cl: 1.6-14.2), in the group with a lower level of homogeneity - 5.4 months (n=96; p=0.024). The significance of the highlighted HI range depended on the fractionation mode used. The median relapse–free survival with fractionation of 3 Gy in the group with HI>=8.5 was 12.7 months (n=38), in the group with a lower level of homogeneity - 8.3 months (n=46; p=0.020). In the group with fractionation regime of 2 Gy: 6.4 and 3.8 months, respectively (n=24/50; p=0.336). The median overall survival in the group with HI>=8.5 was 27.2 months, in the group with a lower level of homogeneity – 21.2 months (p=0.904).
 Conclusion: The level of homogeneity has no significance according to the criterion of overall survival. Despite the fact that this predictor is of value only in scientific terms, the fact of its influence on local control allows to continue research in this direction. This primarily concerns the fractionation regimen with a prescribed dose of 3 Gy.