The concept of local normal tissue damage in the evaluation of treatment planning parameter space

• Main Author: Chavez, Sofia Emilia
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/4038

At present, there is still no systematic approach to the radiation treatment planning process which aims to provide maximum dose to all the tumour cells while the surrounding, normal but critical tissues are minimally irradiated. In fact, the process of treatment plan selection is usually simply based on experience from a large number of past trial-and-error cases in individual cancer centers. In this thesis, two new concepts are introduced, that are demonstrated to be useful tools to rationalize a systematic planning process. 1. The concept of local normal tissue damage (LNTD) : Using a similar concept to that of "cellular damage" in radiobiological models, a concept of a localized "normal tissue damage" is introduced. This simple model is designed to make the best use of current limited clinical estimates of whole organ complication probabilities while providing a coherent framework that will preserve spatial information as well as condense the information into a numerical score for the plan. 2. The concept of parameter space mapping : Treatment parameter mappings will indicate the tissue-specific effect of the dose distribution resulting for the given parameter values. Such mappings can provide very useful insights for treatment plan selection. The use of this new tool is demonstrated in studying the values of the fixation point coordinates for the treatment of uveal melanoma at TRIUMF . Important insight is gained about the effects of the values of the fixation point coordinates on the probable success of the treatment. Such mappings help make treatment planning more efficient, objective and systematic which allows for a better exploitation of the full potential of the proton beam. The above concepts are combined to provide a systematic strategy for treatment planning that will rely on the tissue-specific response to inhomogeneous dose distributions. The LNTD model is used to transform dose distributions into damage maps and then an overall score for that plan can be determined. This score is then used as the information mapped on a fixation point space mapping in order to facilitate selection of a plan. Also, the rationale for the development of multiple-fields is based on the resulting non-linearity of the LNTD(d) curves and hence it is demonstrated that it can be used along with the parameter space mappings in order to successfully plan such a treatment.