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Dosimetric Evaluation and Comparison Between Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated
Murugaiyan Nagarajan1,2, Ramesh Banu2, Balraj Sathya2
1Valvadi Narayanaswamy Cancer Centre, Coimbatore, Tamil Nadu, India.
Aim:
To evaluate and compare the dosimetric parameters between volumetric modulated arc therapy (VMAT) and Intensity modulated radiotherapy (IMRT) in head and neck cancers (HNCs).
Material And Methods:
A total of 30 patients newly diagnosed with Head and Neck cancers planned for radiotherapy were enrolled in the study. Two plans were made for each patient, one VMAT plan with two complete arcs (one clockwise and another counter clockwise ranging from 181° to 179° (clockwise) and 179° to 181° (counter clockwise) and other seven field IMRT dynamic Plan with beam angles at 0°, 50°, 100°,150°, 210°, 260°, 310°. All plans were generated with 6 MV photons. Optimization and calculations were done in Varian Eclipse planning system.
Results:
VMAT plan achieved a better Conformity Index 95% with value of 1.016 ± 0.014 compared to 1.033±0.012 in IMRT. D2%, D5%, D50% were higher in VMAT compared to IMRT. Homogeneity Index was higher for the plans in IMRT with value of 0.035 ± 0.003 compared to 0.058 ± 0.008 with VMAT. The dose to the surrounding organs-at-risk (OARs) are better in VMAT and in particular for brainstem and spinal cord (statistically significant). The monitor units were significantly lower with VMAT (610±70) compared to IMRT (1079± 149).
Conclusion:
VMAT achieved acceptable planning target volume coverage with high conformity to the primary tumor and better sparing effect on organs-at-risk particularly spinal cord and brain stem. Statistically significant reduction in monitor units was achieved in VMAT than in IMRT. VMAT should be preferred wherever feasible with due consideration to cost and availability.
