Dosimetric comparative study of conformal radiation techniques in patients with glioblastoma multiforme

Purpose: The purpose of the current study is to determine whether patients diagnosed with glioblastoma multiforme (GBM) who underwent radiotherapy (RT) using intensity-modulated RT (IMRT) technique were benefitting from this highly conformal treatment in terms of doses received by planning target volume (PTV) and organs at risk (OARs) in comparison to three-dimensional conventional RT (3DCRT). Materials and Methods: Twelve patients treated with IMRT for GBM were selected for dosimetric comparison with 3DCRT. The prescribed dose was 60 Gy in 30 fractions and seven non-coplanner beams were used in IMRT to cover 95% of target volume. The irradiated patients of GBM were retrieved and replanned with 3DCRT techniques. Dosimetric comparison was done by performing two plans for the same patient; prescription dose and normal tissue constraints were identical for both plans. The dose–volume histograms of target volumes and OAR, dose conformity, and dose homogeneity with 3DCRT and IMRT planning were compared. Statistical analysis was performed to determine the differences. Results: The mean conformity index was 0.99 ± 0.001 for IMRT and 0.97 ± 0.002 for 3DCRT, P = 0.001. The mean homogeneity index was 1.03 ± 0.02 for IMRT and 1.06 ± 0.009 for 3DCRT, P = 0.003, which is statistically significant. The IMRT technique enables dose reduction of normal tissues including brainstem (Dmean by 33.78 ± 5.34 and Dmax 51.84 ± 4.43), optic chiasm (Dmean by 36.92 ± 1.99 and Dmax 44.61 ± 3.72), left optic nerve (Dmean by 28.97 ± 6.51 and Dmax 46.08 ± 10.58), right optic nerve (Dmean by 31.93 ± 11.68 and Dmax 44.63 ± 13.54), left eye (Dmean by 18.66 ± 8.92 and Dmax 37.43 ± 13.47), right eye (Dmean by 14.40 ± 4.87 and Dmax 40.37 ± 11.37), left lens (by Dmax 5.45 ± 1.85), and right lens (Dmax 5.07 ± 0.63). Conclusion: The IMRT provides a real dosimetric advantage, especially for normal brain tissue, and in terms of target coverage. It allows treatment of tumors while respecting OARs' dose constraints. The IMRT technique shows significant advantage in PTV coverage, dose homogeneity, and conformity. In IMRT, the coverage is better where PTV was overlapping with critical OARs.