The Use of CT Scanners in Megavoltage Photon-Beam Therapy Planning

Abstract
Several problems related to the true value of quantitative information from CT [computed tomography] scanners in improving estimates of photon beam isodose distribution remain unanswered. Two widely used correction factors provide satisfactory isodose corrections behind heterogeneities of simple geometry. Lateral perturbations were small for megavoltage photon beams used in treating human tumors, indicating that complex computational schemes are uncalled for. It appears doubtful that the use of CT information in megavoltage photon beam isodose curve generation requires larger computers than those currently available in existing therapy planning systems or on the scanner itself or direct access to the CT numbers.