P17.13 Dosimetric comparison and feasibility of simultaneous integrated boost (SIB) in treatment of malignant gliomas using intensity modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT)

Abstract

Abstracts iii119NEURO-ONCOLOGY • MAY 2017 extracted and XRCC1 gene SNPs were analyzed; the allelic discrimination was performed using an ABI PRISM 7900 SDS (Applied Biosystems, Carlsbad, CA, USA) and with validated TaqMan ® SNP genotyping assays (Applied Biosystems). Kaplan Meier curves were performed for statistical association with genotypes. The study has been approved by the local IRB. RESULTS: At the data analysis, the median progression-free survival (PFS) and median overall survival (OS) of these patients were 20 months and 11 months, respectively. A relevant finding of our study was the identification of a XRCC1 genotype that was significantly associated with OS: patients harboring the TT or CC genotype had 12 and 24-month OS ratio of 75 and 16%, respectively, whereas, patients with genotype TC 88 and 34%, respectively. CONCLU-SIONS: The XRCC1 genotype is significantly associated with a shorter OS in GBM patients treated with radiotherapy and temozolomide schedule. The present, pilot study may represent the stimulus to prospectively investigate the role of XRCC1 polymorphisms as a predictive pharmacogenetic marker or as a target for new drug therapies for GBM patients. P17.13 DOSIMETRIC COMPARISON AND FEASIBILITY OF SIMULTANEOUS INTEGRATED BOOST (SIB) IN TREATMENT OF MALIGNANT GLIOMAS USING INTENSITY MODULATED RADIOTHERAPY (IMRT) OR VOLUMETRIC MODULATED ARC THERAPY (VMAT)P. Rapole, G. Karunanidhi, S. Kandasamy, G. Ram Kumar, Sathia Prabhu; Jawaharlal Institute of Post-Graduate Medical Education and Research, Puducherry, India.OBJECTIVE: Simultaneous integrated boost(SIB) is a hypo-fractionation technique wherein the tumor receives different doses to different areas in a single fraction. In our study, we have evaluated the dosimetric feasibility of SIB in the treatment of malignant gliomas and compared the SIB plans of VMAT and IMRT. METHODOLOGY: The patient's MRI (taken four weeks after surgery) and planning CT were used for generating SIB plans with VMAT and IMRT. GPTV is defined as the tumor edema in FLAIR plus a margin of 5 mm. CPTV is defined as the GPTV plus a margin of 2 cm. A dose of 2Gy per fraction was prescribed to the CPTV and 2.4Gy to the GPTV for a total of 25 fractions. The plans were accepted only if they met the set of planning objectives defined in the protocol. The feasibility of SIB planning was evaluated, and the dosimetric data of VMAT and IMRT for SIB planning was compared. RESULTS: The GPTV coverage was significantly better in VMAT than in IMRT (98.67% vs 98.19%;p=0.024). The conformity index for GPTV in IMRT was higher than that of VMAT (0.83 vs 0.76; p=0.001). In contrast to what observed in GPTV, the percentage coverage of CPTV was better in IMRT (97.88% vs 96.87%; p=0.021). But the conformity index of CPTVannulus was higher in VMAT (0.72 vs 0.67; p=0.01). There was no difference in homogeneity index of GPTV and CPTV annulus between the plans. The mean dose received by Normal brain was higher in IMRT than in VMAT (28Gy vs 24.2Gy; p<0.001). Ipsilateral optic nerve has received...

Biological Dose Escalation—Do We Have a New Window of Opportunity in High-Grade Glioma?—A Feasibility Study

“…They also found that MU and treatment time were reduced in the VMAT plan (p < 0.001). 16,17 This particular study did not show any dosimetric advantage of VMAT over IMRT.…”

“…However, other studies have shown some data that are different from ours and this could be due to the smaller sample size in our study. [15][16][17][18] Pragna et al in 2018 did a dosimetric comparison between IMRT and VMAT plan in 28 patients for glioma. Among the two plans, they found that IMRT had better PTV coverage at the expense of mean dose to the brain.…”