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MO_9_2684 - Dosimetric Comparison of Volumetric Modulated Arc Therapy Versus 3-Dimensional Conformal Radiation Therapy in Post-Operative Patients of High Grade Glioma

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Dosimetric Comparison of Volumetric Modulated Arc Therapy Versus 3-Dimensional Conformal Radiation Therapy in Post-Operative Patients of High Grade Glioma
H. B. Singh1, M. Rastogi1, A. K. Gandhi1, R. Khurana1, S. Rath1, S. S. Nanda Sr1, K. Sahni1, R. Hadi1, S. P. Mishra1, A. K. Srivastva1, and A. Bharati2; 1Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, India, 2Dr.Ram Manohar Institute of Medical Sciences Lohia, LUCKNOW, India

Purpose/Objective(s): Radiotherapy technique typically used in the post-operative management of high grade glioma (HGG) is 3-dimensional conformal radiotherapy (3D-CRT). Volumetric modulated arc therapy (VMAT) can provide better coverage of target volumes and sparing of organs at risk (OARs). We aimed to dosimetrically compare 3D-CRT with VMAT plans in the same.

Materials/Methods: Computed tomographic simulation data of 26 patients of HGG fused with post-operative magnetic resonance imaging data and treated with 3D-CRT, were used for dosimetric comparison with subsequently generated VMAT plans. For 3D-CRT, low risk planning target volume (LR-PTV; resection cavity plus edema) was treated to 46 Gray (Gy) in 23 fractions over 5.5 weeks and high risk planning target volume (HR-PTV; resection cavity plus contrast enhancement) was further boosted by 14 Gy in 7 fractions over 1.5 weeks. For VMAT, 46 Gy in 30 fractions was delivered to LR-PTV and simultaneous integrated boost of 60 Gy in 30 fractions to HR-PTV over 6 weeks. Planning objective was to cover ≥ 95% of PTV with 95% of prescription dose. Standard dose constraints were applied to OARs for VMAT planning and tried to be respected in 3D-CRT plan.

Results: Median age was 46.5 years. Left sided and right sided tumors were 46.15% and 53.84%. Tumor location was frontal, parietal, temporal and multi-lobed in 26.92%, 15.38%, 23.0% and 34.6% respectively. Histopathology was glioblastoma multiforme, anaplastic oligodendroglioma and anaplastic astrocytoma in 88.46%, 7.69% and 3.84% patients respectively. Mean PTV D95 (dose received by 95% volume) in 3D-CRT vs. VMAT were 96.66% vs. 98.88% (95% CI -3.23 to -1.20, p<0.001) for LR-PTV and 97.38% vs. 99.01% for HR-PTV (95% CI -2.39 to -0.87, p value<0.001) respectively. Mean conformity index in 3D-CRT vs. VMAT plans for LR-PTV and HR-PTV were 0.96 vs. 0.98 (95% CI -0.032 to -0.011; p<0.001) and 0.97 vs. 0.99 (95% CI -0.025 to -0.009; p<0.001). Mean Dmax (maximum point dose received by the organ) of right optic nerve 31.59 Gy vs. 25.57Gy (95%CI; 0.86 to 11.17;p=0.02), left optic nerve 28.81 vs. 22.14 (95% CI;1.16 to 12.16;p=0.019) optic chiasma 42.24 Gy vs.37.12 Gy (95% CI; -0.11 to 10.37;p=.055),brainstem 50.60 Gy vs. 49.08 Gy (95% CI;-1.50 to 4.53;p =0.31), right lens 5.71 Gy vs. 9.33 Gy (95% CI;-7.94 to 0.80;p=0.10),left lens 5.08 Gy vs. 9.33 Gy (95%CI; -8.32 to 0.19; p=0.040) for 3D-CRT and VMAT respectively. Mean biologically effective dose (BED) for 3D-CRT vs. VMAT were 68.72 Gy vs. 69.20 Gy (95%CI -3.01 to 2.05; p=0.70) for LR-PTV and 72.38 Gy vs. 73.54 Gy (95%CI -1.94 to -0.366; p=0.006) for HR-PTV respectively.

Conclusion: VMAT as compared to 3D-CRT achieved better coverage of the PTV with significant sparing of optic nerve and optic chaisma in post-operative patients of HGG treated with radiotherapy. The sparing of OARs is influenced by the tumor location and laterality.

Author Disclosure: H. Singh: None. M. Rastogi: None. A.K. Gandhi: None. S. Rath: None. A.K. Srivastva: None.

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