One of the goals of conventional external beam radiotherapy is to construct treatment plans for which the dose distribution across the tumor is uniform. This can be achieved with tumor dose heterogeneities of less than 15%. Therefore the concepts of dose response and tumor control probability (TCP) in external beam therapy are clearly defined and unambiguous. However, the treatment of many disease sites in radiation therapy result in high doses to partial volumes of normal tissue structures. For example, in the treatment of pancreatic cancer, the location of the pancreas results in the unavoidable delivery of high doses to the kidneys and spinal cord. The radiation tolerance of the spinal cord is well known. It behaves according to a serial model of radiation damage, which means that a dose in excess of 50 Gy to any region of the spinal cord can produce transverse radiation myelitis. However, the response of kidney is according to a parallel model, i.e., the kidney consists of a large number of repeat units, nephrons, a certain fraction of which must be destroyed before loss of kidney function is observed. The objective of a treatment plan for pancreatic cancer is to manipulate the beam directions and weights, so as to minimize the volume of kidney receiving high dose irradiation in order to reduce the risk of kidney complication, consistent with the prescribed dose to the target volume, and a dose of 003C;45 Gy anywhere to the spinal cord.KeywordsSingle Photon Emission Compute TomographyLinear Energy TransferNormal Tissue Complication ProbabilityTumor Control ProbabilityPhosphor PlateThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.