A Comparative planning and dosimetric study comparing volumetric modulated arc therapy (vmat) vs dynamic intensity-modulated radiation therapy (imrt) in head and neck carcinomas

Background: Introduction of IMRT techniques for the treatment of Head and Neck carcinomas (HNSCC) has given better dose conformity and sparing of the organs at risk (OARs). Disadvantage of fixed angle IMRT is longer radiation delivery time and increased patient exposure to low dose radiation. Recently, VMAT has been developed which enables IMRT-like dose distributions to be delivered using a single rotation of the gantry and thereby reducing the treatment time. This study is undertaken to compare VMAT (single and double arcs) and IMRT plans for dose homogeneity, dose conformity and ability to spare OARs in HNSCC. Aims and objectives: • To compare IMRT and VMAT (Single and double arc) techniques in terms of tumor coverage, conformity and doses received by normaltissues. • To compare the treatment delivery time between IMRT and VMAT (single arc and double arc) in terms of monitor units(MUs). Methods and Materials: Between January 2014 to December 2015, 43 patients with nasopharyngeal, oropharyngeal, hypoharyngeal and laryngeal cancers were taken. IMRT, VMAT single arc and VMAT double arc plans were generated. Comparison of doses using dose volume histogram (DVH) was done. Doses to normal structures, tumor coverage and dose homogeneity and dose conformity was compared. Results: VMAT double arc plans had a superior homogeneity index(HI) equal to (0.1 ± 0.01) [p = 0.001] and best conformity(CI95%=1.2±0.16)[p= 0.02] compared to single arc plans with a HI of (0.1 ± 0.02) and slightly inferior conformity(CI95% = 1.3 ± 0.17) and IMRT plans with a HI of (0.1 ± 0.16) and least conformity (CI95%= 1.3 ±0.23). The average MU needed to deliver the dose of 225cGy per fraction was (637 ± 117.6 MU) [0.001] and (600.7 ± 113.95 MU) for double arc and single arc as against (1121.7 ± 390.27 MU) for the IMRT plan. The average number of monitor units was reduced by 53% for VAMT plans and double arc plans required only 10% more monitor units than single arc plans. Interpretation and Conclusion: VMAT double arc proved a significant sparing of OARs without compromising target coverage compared to IMRT. Hence VMAT is a fast, safe and a better treatment option in our comparison for HNSCC that uses lower MUs compared to IMRT.