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

Objective: To evaluate the dosimetric parameters of Simultaneous Integrated Boost in the treatment of malignant<br />gliomas and compare the SIB plans of VMAT and IMRT. Methodology: CT and MRI of 28 patients were used for<br />generating SIB plans with VMAT and IMRT. A dose of 2Gy per fraction was prescribed to the CPTV and 2.4Gy to<br />the GPTV for a total of 25 fractions. The plans were accepted only if they met the set of planning objectives defined<br />in the protocol. Results: We could achieve the planning objectives in all the SIB plans. Although GPTV coverage was<br />statistically better in VMAT (98.67% vs 98.19% ;p=0.024) the difference is not clinically meaningful. The conformity<br />index for GPTV was higher in IMRT (0.83 vs 0.76; p=0.001). The coverage of CPTV was better in IMRT<br />(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).<br />There was no difference in homogeneity index of GPTV and CPTV annulus between the plans. The mean dose received<br />by normal brain was higher in IMRT (28Gy vs 24.2Gy; p<0.001). Ipsilateral optic nerve has received lesser Dmax in<br />IMRT (44.2Gy vs 46.95Gy; p=0.02). No difference was seen in Dmax of brainstem, optic chiasm, contralateral optic<br />nerve. The treatment times and monitor units were significantly less in VMAT. Conclusion: SIB is dosimetrically<br />feasible for hypofractionation in malignant gliomas using IMRT and VMAT. IMRT plans had better boost conformity,<br />lower ipsilateral optic nerve and brainstem maximum doses compared to VMAT. Whereas, VMAT had better coverage,<br />better overall PTV conformity, lower normal brain mean dose, lower monitor units and lesser treatment times. Although<br />planning of VMAT is cumbersome and time consuming, the advantage of reducing treatment time is beneficial to<br />the patients' comfort and better managing of patient load in high volume centres.