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Integrating a Portable CT to a Single Room Proton Machine for Imaging Guided Proton Therapy (IGPT)

B Sun

B Sun*, T Zhang , S Goddu , L Santanam , J Bradley , S Mutic , T Zhao , Washington University School of Medicine, St.louis, MO


WE-RAM2-GePD-J(B)-3 (Wednesday, August 2, 2017) 10:00 AM - 10:30 AM Room: Joint Imaging-Therapy ePoster Lounge - B

Purpose: Sparing of organs-at-risk are often compromised in proton therapy due to the uncertainties in tumor localization and intra- and inter-fractional anatomy changes. As simple alignment based on bony anatomy or fiducials cannot guarantee coverage and sparing, online dose calculation is of warranted with IGPT). Due to its inaccurate Hounsfield Units, CBCT is not ideal for treatment adaption in proton therapy. We integrate a portable helical CT scanner into a compact proton unit and evaluate the localization accuracy for 3D volumetric IGPT and proton dose calculations.

Methods: The portable CT scanner was placed parallel to the setup positon of the 6D robotic couch, which required a 90 degree rotation of the couch between the setup and imagining position. A rigid reference frame with 4 radiopaque fiducials monitored by a ceiling-mounted camera was attached to the couch to maintain the rigid transformation between the couch and the room coordinates within 0.5mm. Images acquired with the CT scanner were used for patient setup and retrospective verification of the original plan with true fractional dose calculated on volumetric setup image. Physician reviewed the verification plan offline and ordered re-planning if necessary.

Results: The portable CT passed successfully our test on image quality and the geometric accuracy is within 1mm in all three dimensions. The localization accuracy was measured better than 1mm/1 degree including all uncertainties from the couch, CT scanner and machine isocentricity. The whole imaging and localization process took about 20 minutes in IGPT treatments. A stoichiometric CT calibration curve was commissioned in our treatment planning system for the calculation of true fractional dose on images from the CT scanner.

Conclusion: The use of portable CT scanner in proton therapy enhances our capability to localize tumors in soft tissue and provides additional benefits for off-line dose evaluations with superior CT imaging quality.

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