To segment or not to segment the PTV in SIB-VMAT of head-and-neck cancer: a dosimetric comparison with relevance to clinical practice

Aim: This study aimed to evaluate and compare simultaneous integrated boost-based volumetric modulated arc therapy (SIB-VMAT) of head-and-neck plans optimised using segmented and non-segmented intermediate-risk target volumes. Materials and methods: CT data of 20 patients with locally advanced laryngeal cancer treated with radical chemoradiation were included retrospectively. Both segmented [planning target volume (PTV) IR!] and non-segmented PTV (PTV IR) volumes were created for the intermediate-risk volume. Correspondingly, two VMAT plans were generated for every CT dataset. Dosirnetry parameters obtained from cumulative dose volume histogram and the quality indices such as conformity and homogeneity indices were evaluated for both plans and were statistically analysed. Results: Maximum dose of PTV IR! was observed to be higher in the non-segmented plans (7281.45 versus 7075.75 cGy) and was statistically significant (p = 0.002). Homogeneity index (HI) of PTV IR! in segmented plans fared better compared to non-segmented plans (0.1 versus 0.12, p = 0.01). All other dosimetry parameters were found to be similar in both plans. Conclusion: This study shows that using segmented volumes for planning will lead to more homogenous plans with regard to intermediate- and low-risk volumes, especially under controlled settings.