SU‐F‐J‐31: Dual Energy Imaging in the Treatment of Head and Neck Tumors: A Phantom Study

Abstract

Purpose:Organ motion, due to swallowing, can significantly affect the PTV margins used in head and neck patients. Evaluation of swallowing motion 2016 AAPM Annual Meeting Program Medical Physics, Vol. 43, No. 6, June 2016 3412 3412 may be performed using x‐ray fluoroscopy. However, regions such as the soft palette and epiglottis may be difficult to visualize due to the presence of bone (mandible, teeth). The goal of this phantom study is to determine if dual energy (DE) subtraction would improve the visualization in these regions.Methods:An Alderson head/neck anthropomorphic phantom was positioned on the treatment table of the linac (iX, Varian Medical Systems, Palo Alto, CA). Lateral single energy (SE) kV images of the phantom were obtained with the On‐Board Imager (OBI) using our standard protocol (70 kVp, 3.2 mAs). Subsequently, DE images were obtained sequentially at 60 kVp and 120 kVp. The mAs settings for the individual DE component images were determined by varying the x‐ray exposure time, while maintaining a constant tube current, with the goal of producing a dose at the surface that was comparable to the SE dose. Subtraction images were created offline using in‐house software.Results:Optimal DE images were produced using 120 kVp (0.5 mAs) and 60 kVp (2 mAs). The DE images showed good subtraction of the overlying bony anatomy. In particular, subtraction of the mandible resulted in improved visualization of the airway and soft palette. An analysis of the relative contrast of the soft palette showed an increase of 25–400% using DE vs. SE. The imaging dose at the surface was estimated as 0.22 mGy using SE and 0.23 mGy using DE.Conclusion:DE imaging may provide an effective means for visualizing the soft palette and epiglottis in head and neck cancer patients. Combining such an approach with fluoroscopy may provide data on organ motion due to swallowing that may be incorporated in PTV design.