Intensity-modulated radiotherapy, volume-modulated arc therapy and helical tomotherapy for locally advanced nasopharyngeal carcinoma: a dosimetric comparison

Background: To evaluate the potential dosimetric gains of helical tomotherapy (HT) versus intensitymodulated radiotherapy (IMRT) or volume-modulated arc therapy (VMAT) for locally advanced nasopharyngeal carcinoma (NPC). Methods: A total of 30 locally advanced NPC patients were recruited to receive IMRT, VMAT optimized with Eclipse treatment planning system (TPS) (Version 11.0.31) and HT using TomoTherapy Hi-Art Software (Version 2.0.7) (Accuray, Madison, WI, USA). All three techniques were optimized for simultaneously delivering 60.06 Gy to PTV1 and 50.96 Gy to PTV2. Homogeneity index (HI) and conformity index (CI) of PTVs, dose volume histograms (DVHs), treatment delivery time and monitor units (MUs) were analyzed. Results: No significant difference existed in planning target volume (PTV) coverage among IMRT, VMAT or HT. However, mean HI of PTV1 was better with HT (0.16) and IMRT (0.16) than VMAT (0.20). And mean HI of PTV2 was better with HT (0.30) and IMRT (0.31) than VMAT (0.33). Mean CI of PTV1 was also better with HT (0.80) than IMRT (0.74) and VMAT (0.75). Mean CI of PTV2 was better with HT (0.66) than IMRT (0.62) and VMAT (0.63). Except for optic nerve and chiasm, the mean/maximal dose of OARs declined significantly in HT. For normal tissue adjacent to PTV, HT could significantly lower V5, V10, V20 and V60 than IMRT/VMAT. And shorter delivery time per fraction and MUs were observed for VMAT. Conclusions: For locally advanced NPC patients, HT has superior outcomes in terms of PTV coverage and OARs sparing as compared with IMRT/VMAT. And VMAT shows reduced treatment delivery time and lower MUs than IMRT/HT.