Estimation of radiotherapy modalities for patients with stage I-II nasal natural killer T-Cell lymphoma

PURPOSE: The objective of this study is to estimate radiotherapy (RT) modalities for patients with stage I-II nasal natural killer T-Cell lymphoma (NNKTCL), including plan quality, radiation delivery efficiency, cost of RT and excess absolute risk (EAR). MATERIALS AND METHODS: Twenty-four representative patients with stage I-II NNKTCL treated with fix-field intensity-modulated radiotherapy (FF-IMRT) were re-planned for volumetric modulated arc therapy (VMAT), TomoDirect (TD) and TomoHelical (TH) on the TomoHDA system, respectively. Plan characteristics, cost of RT and EAR were compared. RESULTS: Compared with IMRT, TD and TH showed significant improvement in terms of D(98%), D(2%), cold spot volume and homogeneity index (HI) of planning target volume (PTV), while achieving worse D(mean) and conformity index (CI). The mean dose of oropharynx, thyroid and left salivary, and the maximum dose of right salivary by TD (249.20%, p=0.000; 52.94%, p=0.000; 160.23%, p=0.022; 122.67%, p=0.027), VMAT (15.76%, p=0.000; 23.53%, p=0.000; 34.09%, p=0.000; 31.33%, p=0.000) and TH (250.32%, p=0.000; 58.82%, p=0.000; 120.45%, p=0.020; 117.33%, p=0.032) increased significantly compared to IMRT. VMAT reduced treatment time (p=0.000; 0.000; 0.000) and monitor units (MUs) (p=0.000; 0.000; 0.000) obviously compared with IMRT, TD and TH. The cost of RT for TD and TH increased 150% compared with IMRT and VMAT. IMRT obtained the lowest EAR to oropharynx, thyroid, left and right salivary gland in the four treatment modalities. CONCLUSION: The results show that both TD and TH can achieve higher conformal target quality while getting worse organs at risk (OARs) sparing and EAR to some organs than IMRT for patients with stage I-II NNKTCL. IMRT delivers the lowest dose to most OARs, VMAT requires the lower cost of RT and shortest delivery time, and TH obtained the optimal target coverage. The results could provide direction for selecting proper RT modalities for different cases.