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Development of ultrasound guided radiotherapy of the cervix and kidneys

Sarah Mason is a PhD Student in the Imaging for Radiotherapy Adaptation team and is investigating the use of ultrasound to reduce treatment margins in radiotherapy. 

Highly conformal radiotherapy planning techniques such as IMRT and VMAT are only possible if the precise positions of the target volume and organs at risk are known. However, the motile and deformable characteristics of soft tissue organs make it extremely difficult to ascertain their position (despite daily x-ray imaging and careful patient set up) prior to and during radiation delivery. Therefore, large treatment margins are required to ensure adequate coverage of the target area at the expense of including healthy tissues in the treatment field. Daily soft-tissue imaging using ultrasound is a promising solution for determining the precise location of the target organ and surrounding tissues for radiotherapy, which could ultimately allow a more widespread use of highly conformal delivery plans.

Ultrasound provides real-time, good contrast images of soft tissues at zero dose and a relatively low cost. Additionally, ultrasound-imaging systems have been designed specifically for use in the radiation treatment room setup, and can return positional information with each image obtained. Preliminary results indicate that images of the kidney and uterus with well-defined boundaries can be obtained and can be segmented manually. Current work involves developing automatic segmentation algorithms that allow the organ of interest to be identified and tracked on ultrasound images such that their exact location in the treatment room at any point in time can be determined. The uterus and kidneys will serve as model systems to illustrate the success and adaptability of ultrasound segmentation techniques, and will suggest how ultrasound-based motion tracking can be used to improve the efficacy and safety of radiation therapy.  A clinical study to demonstrate the improvement in image quality and motion estimation of the uterus provided by ultrasound imaging over established X-ray imaging techniques is underway.