Emission guided radiation therapy: a feasibility study
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The effectiveness of cancer treatment is compromised by the need to reduce the uncertainties originating from a variety of factors including tumor volume delineation, patient setup, and irregular physiologic motion. In particular, effective yet practical tumor motion management remains a major challenge in current external beam radiation therapy. Many strategies such as motion encompassment, breath-hold techniques, and respiratory gating have been proposed in the literature and implemented clinically. These methods have shown success in certain situations with different limitations. With the advent of image guided radiation therapy, real-time tumor tracking methods have become popular in clinics to proactively address the challenge with on-board tumor localization. Nevertheless, such techniques rely on surrogate signals and have been reported vulnerable to errors. In this dissertation, EGRT is proposed as a new modality for effective and practical management strategy of cancer treatment uncertainties. One implementation of EGRT is to use PET emissions in real-time for direct tumor tracking during radiation delivery. Radiation beamlets are delivered along PET lines of response by a fast rotating ring therapy unit consisting of a linear accelerator and PET detectors. A complete treatment scheme with capabilities of accurate tumor tracking and dose planning is proposed to implement this EGRT concept. Simulation studies with physical phantom, 4D digital patient model, and clinical patient datasets are carefully designed to evaluate the feasibility and performance of EGRT. We show that with the capabilities of achieving both tumor tracking and sophisticated intensity modulation, EGRT has the potential to enable an effective implementation of 4D radiation therapy with true biological targeting and other advantages.