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Split-Field Or Whole-Field IMRT for Head and Neck Cancer Treatment with Daily Localization Uncertainty?

T Lin

T Lin*, L Wang , T Galloway , C Ma , Fox Chase Cancer Center, Philadelphia, PA


TU-C3-GePD-J(B)-4 (Tuesday, August 1, 2017) 10:30 AM - 11:00 AM Room: Joint Imaging-Therapy ePoster Lounge - B

Purpose: Radiation of H&N cancer can be accomplished using two methods: split-field IMRT(SFI),in which LAN is treated with a separate anterior field and extended-whole-field IMRT/VMAT(WFI) in which LAN is included with IMRT/VMAT field. Larynx can be better spared by SFI; however,with daily localization uncertainties,larynx could receive extra dose at the matching line. This study is to determine if SFI has advantage of sparing larynx in image-guided-radiation-treatment.

Methods: Nine H&N cases were included in this study. Both SFI and WFI at upper target coverage were generated with VMAT. Same 70Gy(high risk) and 60Gy(intermediate risk) with 63Gy and 56Gy for secondary target coverage were applied to target. Larynx sparing could also be observed through its mean dose. 30 kV-CBCT images during treatment course for each patient were delineated including contralateral, ipsilateral targets and larynx. About 300CBCT images with daily delivered doses were compared in a form of dose-volume-histograms.

Results: Average dose for Larynx with WFI was 37.0Gy as planned with the simulation CT and that for SFI was 17.4Gy. Normalized daily larynx doses to the prescription doses for WFI and SFI indicated that SFI with daily localization uncertainties resulted in 10% higher mean larynx dose,which was lower than that with WFI(15%); however,SFI showed much higher hot spots in the larynx and much lower cold spots in the target than WFI.

Conclusion: Patients treated with SFI indeed showed more sparing at the treatment planning than those with WFI with identical target coverage; however,lower cold spots in the target and higher hot spots in the larynx were observed in the 9 patients studied after summing up dose distributions from all 30 image-guided treatment fractions. These cold spots in the target may result in treatment failures and the hot spots in the larynx may have a detrimental effect on the organ function.

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