A control circuit forms a radiation therapy treatment plan by automatically generating a base dose that references dosing information from multiple sources and then using that base dose to optimize a radiation therapy treatment plan. That radiation therapy treatment plan is then used to administer radiation therapy to a patient. That automatically generated base dose can represent any or all of earlier radiation therapy treatments for the patient, a same fraction as a dose presently being optimized per the radiation therapy treatment plan, and future planned fractions for the patient.