Potential of helical tomotherapy to reduce dose to the ocular structures for patients treated for unresectable sinonasal cancer.
OBJECTIVE
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
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 Medial Systems, Palo Alto, CA) and Tomotherapy HI-ART treatment planning system (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 "hot-spots." 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.
Department of Radiation Oncology, University of California Davis Cancer Center, Sacramento, CA, USA. allen.chen@ucdmc.ucdavis.edu
Allen M
AM
Chen
Radhika
R
Sreeraman
Mathew
M
Mathai
Srinivasan
S
Vijayakumar
James A
JA
Purdy
D002294:Carcinoma, Squamous Cell / Q000175:diagnosis / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D005123:Eye / Q000528:radiation effects*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008444:Maxillary Sinus Neoplasms / Q000175:diagnosis / Q000532:radiotherapy*; D009367:Neoplasm Staging; D009669:Nose Neoplasms / Q000175:diagnosis / Q000532:radiotherapy*; D058958:Organs at Risk; D011832:Radiation Injuries / Q000517:prevention & control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D018570:Risk Assessment; D012494:Sampling Studies; D036542:Tomography, Spiral Computed; D016896:Treatment Outcome