MRI Only Radiation Therapy With CPAP

Patients will undergo both CT and MRI prior to abdominal radiation therapy and CBCT and orthogonal kV/MV images prior to each treatment delivery. A two arm study will be performed and patients will be enrolled into a given arm according to their eligibility. Arm 1 is for patients that are either not eligible for CPAP or that are unable to tolerate CPAP. These patients will undergo breath-hold and 4D imaging for both CT and MRI without CPAP. Arm 2 is for patients that are eligible for CPAP and able to tolerate CPAP. These patients will undergo breath-hold CT without CPAP, 4D-CT with and without CPAP and 4D-MRI with CPAP. Two specific aims will be investigated. In Aim 1, we will explore the feasibility of using a MRI-only in Radiation Oncology workflow. A probabilistic classification method will be utilized to generate a pseudo-CT from MRI to support treatment planning and image guidance for radiation therapy. The quality of the pseudo-CT will be evaluated by comparing it with CT. In addition, the reverse mapping will be investigated to create pseudo-MRI from CBCT to improve visualization of treatment targets and soft tissue prior to treatment delivery. In Aim 2, we will evaluate the utility of CPAP as a novel motion reduction methodology for patients with liver and pancreas cancer, to this end CT images with and without CPAP will be used. The evaluation will be based on the changes of motion magnitude, the achievable volumetric reduction in treatment target volumes, and doses to the targets and critical organs.