These instructions provide guidelines for preparing manuscripts for submission to the Conference Record (CR) of the 2016 IEEE Nuclear Science Symposium and Medical Imaging Conference. If you are using Microsoft Word to prepare your manuscript, you should use this document as a template. Define all symbols used in the abstract. Do not cite references in the abstract. Do not delete the blank line immediately above the abstract; it sets the footnote at the bottom of this column. Proton computed tomography has been suggested as an imaging technique alternative to x-ray CT for proton therapy treatment planning and image guidance. Dose, image quality, and range prediction accuracy are closely related and the calculation of the dose delivered during a proton CT scan is crucial for characterizing a proton CT scanner. Here we report on the dosimetric evaluation of proton CT scanner using a prototype built by the pCT collaboration between Loma Linda University, the University of California Santa Cruz, and Baylor University. The Catphan CTP554 16 cm acrylic dose phantom, representing a human head, was used to measure the dose to water during a typical proton CT scan at the Northwestern Medicine Chicago Proton Center in Warrenville, Illinois. A Farmer ionization chamber was installed in two locations (centre and periphery of the phantom) and the accumulated charge was measured with the 35040 Advanced Therapy Dosimeter (Fluke Biomedical). The proton CT scanner was exposed to a uniform beam profile of 200 MeV protons on the uniform scanning clinical proton beam line. At a rate of 1 M protons sec it takes 7 minutes in order collect about 400 M protons during a continuous 360 deg rotation. Theproton fluence at the level of upstream inner tracker planes during the 7 minutes of exposure was estimated to be 1.4 M protons/cm2. The dose to water was 1.46 mGy in the peripheral location and 1.48 mGy in the central location, demonstrating that it is practically uniform across the phantom. According to these results, we can conclude that, based on an initial dosimetric characterization of a prototype pCT scanner conducted on a clinical proton beam line, proton CT is a promising modality for low-dose image guidance and adaptive proton therapy.