|M.Sc Student||Band Miriam|
|Subject||Robust Optimization Applied to Intensity Modulated|
Radiation Therapy Treatment Planning
|Department||Department of Industrial Engineering and Management||Supervisor||Professor Emeritus Aharon Ben-Tal|
|Full Thesis text|
Cancer is one of the leading causes of mortality in the world and advances in therapy are crucial for patient longevity. More than half the cancer patients in the United States and Israel are treated using radiotherapy, and accurate targeting is essential to its effectiveness. Intensity-modulated radiation therapy (IMRT) is an advanced technique that directs x-rays at the patient in a very conformal way. The basic idea is to direct beams at the tumor and at the same time limit the radiation dose delivered to the normal tissue and surrounding organs at risk (OAR). The physicists at Rambam Health Care Center’s oncology department, a leading cancer treatment center, perform the aperture-based inverse planning (ABIP) to set an optimal treatment plan. We model the ABIP stage as a linear program (LP) optimization problem and obtain treatment plans comparable to those obtained by the currently used treatment planning system (TPS). We demonstrate how patient positioning and organ or tumor motion between the treatment sessions affect the actual doses delivered to the tumor and OAR regions. A probability model is presented to obtain a treatment plan that protects against slight deviations in the original tumor and organ locations. The methodology of robust optimization (RO), which transforms our LP into a second order cone program, is described. We compare the RO solutions to the conventional margin approach in which the tumor contours are simply widened to account for movement and additional errors. Our results show that this technique is a practical way of incorporating uncertainties into the treatment planning process and enhances OAR sparing. Much study remains to be done before this technique can be implemented clinically, to save and improve the lives of cancer patients around the world.