Considerations of lung tumor motion during radiation therapy

Eric W Pepin, Purdue University

Abstract

The purpose of this dissertation was to investigate the effects of respiration on the motion of lung tumors and explore the impact on radiation therapy. The accurate delivery of radiation to lung lesions has long been challenged by respiratory induced tumor motion. Current clinical solutions have been designed to forcibly limit the tumor motion; these methods have been hindered by patient discomfort and involuntary motion. With a more complete understanding of the patterns, behaviors, and tendencies of respiratory induced tumor motion, it may be possible to treat lung tumors with radiation while the patient is breathing ad libitum. A three phase investigation sought to characterize lung tumor motion and provide clinically implementable solutions that permit free breathing. In the first phase, tumor motion was characterized by the size and shape of the motion space. This resulted in a taxonomy of motion space shape and extent that was correlated to tumor location. The second phase examined an existing method for treatment of tumor under free breathing conditions. The sources, directions, and magnitudes of error were investigated, resulting in a clinical recommendation for compensatory action based on tumor location. The last phase proposed a new method for the treatment lung tumors in patients breathing ad libitum. In a proposed modification to respiratory-gated therapy, a dynamic End-of-Exhale gating window was introduced to address the issue of baseline shift. Two methods of adjustment were developed and evaluated for a range of input parameters. The performance of each method was evaluated in terms of the duty cycle it achieved during simulated treatments. A comparison with the ideal window and the existing static window revealed the potential for benefit, but also imperfections in the identification of the End-of-Exhale breathing state and in the placement of the gating window about the End-of-Exhale breathing state. The results of this research have the potential to reduce the targeting and delivery errors associated with the radiation therapy of moving lung tumors under free breathing conditions, and ultimately inform the development of a model that accurately predicts the motion of such lung tumors during treatment, eliminating respiratory effects on radiation therapy.

Degree

Ph.D.

Advisors

Wu, Purdue University.

Subject Area

Medical imaging|Oncology

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