Potential of helical tomotherapy to reduce dose to the ocular structures for patients treated for unresectable sinonasal cancer

Purpose: To compare intensity-modulated radiotherapy (IMRT) treatment plans generated by segmental multileaf collimator (SMLC) and helical tomotherapy (HT) techniques for patients with unresectable sinonasal cancer. Methods and Materials: SMLC-IMRT and HT-IMRT plans for 5 patients with cancer of the paranasal sinuses and nasal cavity were independently optimized using the Eclipse treatment planning system (Varian MedialSystems, Palo Alto, CA) and Tomotherapy HI-ART treatment planningsystem (Tomotherapy, Inc, Madison, WI). The goal was to deliver a prescribed dose of 70 Gy to at least 95% of the planning target volume (PTV) encompassing gross tumor over 35 treatments whereas respecting constraints to organs at risk, notably the ocular structures. Results: HT-IMRT reduced the maximum doses to the optic chiasm, as well as to the ipsilateral optic nerve and retina (P < 0.05, for all). Maximum doses to these structures were reduced by 10%, 16%, and 14%, respectively, using HT-IMRT compared with SMLC-IMRT. Additionally, the mean dose to the ipsilateral lacrimal gland was reduced by 32% using HT-IMRT. With respect to conformality, HT-IMRT improved dose homogeneity by decreasing "hotspots." The mean percentage of PTV70 receiving greater than 77 Gy (110% of the prescribed dose) was 4.0% for the HT-IMRT plans compared with 17.8% for the SMLC-IMRT plans (P = 0.001). Conclusions: HT-IMRT has the potential to improve dose homogeneity to PTVs whereas reducing dose to the optic structures. Clinical implications are discussed.