Optimization of Carbon Ion Treatment Plans by Integrating Tissue Specific α/β-Values for Patients with Non-Resectable Pancreatic Cancer.

Abstract

BackgroundThe aim of the thesis is to improve treatment plans of carbon ion irradiation by integrating the tissues’ specific -values for patients with locally advanced pancreatic cancer (LAPC).Material and MethodsFive patients with LAPC were included in this study. By the use of the treatment planning system Syngo RT Planning (Siemens, Erlangen, Germany) treatment plans with carbon ion beams have been created. Dose calculation was based on -values for both organs at risk (OAR) and the tumor. Twenty-five treatment plans and thirty-five forward calculations were created. With reference to the anatomy five field configurations were included. Single Beam Optimization (SBO) and Intensity Modulated Particle Therapy (IMPT) were used for optimization. The plans were analyzed with respect to both dose distributions and individual anatomy. The plans were evaluated using a customized index.ResultsWith regard to the target, a field setup with one single posterior field achieves the highest score in our index. Field setups made up of three fields achieve good results in OAR sparing. Nevertheless, the field setup with one field is superior in complex topographic conditions. But, allocating an -value of 2 Gy to the spinal cord leads to critical high maximum doses in the spinal cord. The evaluation of dose profiles showed significant dose peaks at borders of the -gradient, especially in case of a single posterior field.ConclusionOptimization with specific -values allows a more accurate view on dose distribution than previously. A field setup with one single posterior field achieves good results in case of difficult topographic conditions, but leads to high maximum doses to the spinal cord. So, field setups with multiple fields seem to be more adequate in case of LAPC, being surrounded by highly radiosensitive normal tissues.