The purpose of this study was to characterize a mobile helical CT system for adaptive proton therapy on a compact double scattering proton therapy system at our institution and to assess the dosimetric implications of planning with the mobile CT system. We started by validating the stopping power curve of our clinical CT simulator. An electron density phantom was scanned with varying plug patterns, table heights, and mA. CT numbers were acquired for each plug (mean and standard deviation). A stoichiometric algorithm was used to acquire stopping power ratios for the CT simulator. The same procedure was repeated to acquire CT numbers and stopping power ratios for the mobile CT system. To confirm the dosimetric equivalence of the two CT to stopping power curves, clinical treatment plans were generated on an anthropomorphic thorax, pelvis, and head phantom. The plans were created on each phantom based on the CT Simulator and clinical stopping power curves. On the thorax phantom, a 62.6 cc spherical PTV was placed onto the posterior right upper lobe. A 78.5 cc prostate PTV was adapted from a clinical treatment plan. On the head phantom, a 19.8 cc spherical PTV was placed in the medial posterior brain. The brain and lung PTV were prescribed 60 Gy in 30 fractions. The prostate PTV was prescribed 78 Gy in 39 fractions. Using the adaptive workflow in the treatment planning system, the clinical treatment plan was copied onto the imported and aligned mobile CT scan for dose comparisons. Clinical metrics of the dose volume histograms were evaluated for dose agreement between critical structures. A gamma analysis consisting of distance-to-agreement and absolute dose comparisons was used to evaluate dosimetric deviation between plans. This analysis was accomplished using our clinical QA software and was evaluated at treatment isocenter in the coronal, sagittal, and transverse planes. All treatment plans passed QA gamma analysis (3% dose difference, 3 mm distance-to-agreement) at isocenter in the coronal, sagittal, and transverse planes. The prostate, thorax, and head plans passed with minimum of 100%, 96.2%, and 94.7% passing points at isocenter in each plane. Mean PTV dose deviation was 0.2 Gy, 0.4 Gy, and 0.8 Gy for lung, prostate, and brain, respectively. Max PTV dose deviation was 0.5 Gy, 0.6 Gy, and 0.1 Gy for lung, prostate, and brain, respectively. Based on this study, the Mobius AIRO Mobile CT System and our SPR curve developed from an electron density phantom provides comparable treatment plans to our CT simulator and thus, can be used for adaptive proton therapy on the compact double scattering proton therapy system at our institution.