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.
Chen
Allen M
AM
Department of Radiation Oncology, University of California Davis Cancer Center, Sacramento, CA, USA. allen.chen@ucdmc.ucdavis.edu
Sreeraman
Radhika
R
Mathai
Mathew
M
Vijayakumar
Srinivasan
S
Purdy
James A
JA
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