ProKnow plan studies will provide participants with planning images (e.g. series of axial CT images) and patient anatomy (structure set with target and organs-at-risk already contoured).
Most treatment planning systems (TPS) require the user specify a conversion table to allow CT pixel values to be converted to an electron density matrix that is required for the dose calculation. This is often called a "CT-to-ED" table. Because you are getting planning images from a different scanner than you use in your clinic, you should just assign one of your standard, clinical CT-to-ED tables that you already have on hand for kilovoltage (kV) CT. There is some variation in density conversion from CT to CT, but not enough to have a major impact on the study.
For more background on CT pixel values and conversion to electron density, you can check out this video.