Determination and use of radiobiological response parameters in radiation therapy optimization (in English)

In the present thesis, a treatment optimization procedure is used that considers the shape and the structure of the target tissues and healthy organs at risk, their relative position and their dose‐response relations for the individual patient. Mathematical models largely based on the Poisson statistics and the linear‐quadratic model of cell kill, have been used to quantify the radiobiological response of normal human tissues and tumors to radiation therapy. The radiobiological parameters D 50 , γ, s , and V refof the Poisson and relative seriality models have been estimated for certain normal tissues and targets. The determination of these dose‐response relations was based on clinical materials where the treatment information and follow‐up records of the individual patients were available. The clinical use of the derived dose‐response relations is demonstrated through a biological evaluation procedure, which is applied to certain clinical cases. This procedure uses the biological models and dose‐response data of the involved organs and optimizes the dose level of the treatment technique under study. The clinical value of biologically based treatment planning is compared with alternative physical criteria and with the judgment of personnel. It is demonstrated that the radiobiological objective functions allow a much higher conformity and a more clinically relevant scoring of the treatment outcome. In these cases the reliability of the patient setup becomes critical for the effectiveness of the treatment. It is realized that accurate information concerning the response of different organs to fractionated intensity modulated radiation therapy is the key to true optimization of the delivered dose distribution.