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WE-A-WAB-01: New Technologies Addressing the Range Uncertainty of Proton Therapy.

The role of proton therapy in radiation therapy is currently expanding. In the U.S., there are at present 11 clinical proton treatment facilities, with 10 centers operating proton gantries and 6 additional facilities under construction. One of the main challenges in proton therapy is the uncertainty in predicting proton range. Range uncertainties in proton therapy are related to ambiguity in converting x-ray CT attenuation data to proton relative stopping power and are further compounded by organ deformation and internal motion as well as increasing relative biological effectiveness in the distal part of proton beams. Closely related to this issue is the continued development of image guidance technology in the treatment room that ideally will provide feedback for in-room treatment plan modifications (adaptive proton therapy). Proton therapy treatment planning applies quite substantial range uncertainty margins, negating, in part, some of the advantages of the finite range. The problem of range uncertainty in proton therapy has been addressed in many ways, the ultimate goal being to reduce this uncertainty to ∼1 mm. Approaches to address this problem include Monte Carlo simulations to study the effects of different sources on proton range uncertainty, studies showing the amount of range uncertainties in patients, robust planning techniques, and various technological and calibration methods that attempt to improve the accuracy of relative proton stopping power and to detect and minimize range errors at the time of treatment, e.g., dual energy CT scanners, proton CT and radiography, prompt gamma registration and monitoring of proton radiation therapy with PET imaging. This symposium will present a broad overview of the current status of modern computational and imaging approaches to addressing the range-uncertainty problem of proton beams in radiation therapy.


LEARNING OBJECTIVES
1. Understand the prevailing range uncertainties in proton therapy and how they can affect clinical practice. 2. Learn how the magnitude of range uncertainties has been studied with Monte Carlo simulations and in patients. 3. Get an overview of new technologies addressing the range uncertainty problem in proton therapy. 4. Learn about principles of proton computed tomography and radiography and how these techniques may be used for better range definition and pre-treatment quality assurance. 5. Learn about the use of prompt gamma emission for proton therapy range verification. 6. Learn about the different implementations and initial clinical experience of PET verification of treatment delivery in proton and ion therapy.