Comparison of daily versus nondaily image-guided radiotherapy protocols for patients treated with intensity-modulated radiotherapy for head and neck cancer.

Background: The purpose of this study was to determine the feasibility of nondaily image-guided radiotherapy (RT) strategies with intensity-modulated radiotherapy (IMRT) for head and neck cancer.

Methods: Alignment data was analyzed from 103 consecutive patients treated by IMRT for head and neck cancer who had undergone daily imaging with onboard mega-voltage CT (MVCT), resulting in 3275 images. Geometric setup errors that would have occurred using less-than-daily imaging were hypothetically estimated for 4 temporal less-than-daily image-guided RT protocols.

Results: For image-guided RT on the first fraction, weekly image-guided RT, first 5 + weekly image-guided RT, and alternating day image-guided RT, the respective incidences of geometric miss were 50.5%, 33.8%, 30.1%, and 15.7% assuming 3-mm uncertainty margins; and 18.7%, 11.7%, 10.3%, and 4.1% with 5-mm margins.

Conclusion: Less-than-daily image-guided RT strategies result in a high incidence of potential miss when 3-mm uncertainty margins are utilized. Less-than-daily image-guided RT strategies should incorporate margins of at least 5 mm.