The Research Of Radiobiological Effect Mathematic Model Based On Equivalent Uniform Dose

Radiation oncology is now developing in two directions: 1. Change in fraction size and optimization in radiotherapy planning. 2. Improvement in dose distribution. Both of these have to be based on accurate assessment of tumor sensitivity and organs at risk. The Dose-Volume-Histogram (DVH) is a method used to estimate the clinical effects on various tissues, but it still has many deficiencies. First of all, for plans with the same statistical values but different dose distributions, it is not possible to compare the radiobiological response. Secondly, in describing the planning, it is only possible to use a few dose point values, and finally, with regard to different fractionation doses with the same total dose, the plans again cannot be compared.Based on Niemierko's study, this paper takes into consideration the proliferation of cancer cells during irradiation, as well as the original equivalent uniform dose (EUD) mathematical model, to which we have added the variable of potential doubling time. The improved model allows the comparison of different fraction doses, different gradients of dose distribution and different intervals between fractionated irradiation, thus overcoming some of the deficiencies inherent in DVHs.With changes in parameters, by comparing the 1995 and 1999 versions to the changes and trends of EUD + Tpot, we could determine the weight of these parameters in our model, the differences and connections between various models, as well as their characteristics and conditions of appropriate use.In 40 lung cancer patients receiving radiotherapy, the pulmonary EUD and the traditional dose-volume parameters were compared for their validity in the statistical assessment of normal tissue complications. This study suggests that EUD can overcome the difficulties in evaluating different planning images, different biological effects on lung tissue due to different fractionation schedules and can also predict radiation damage, and thus would have some clinical value.This study also evaluated 6 cases of cancer treated by hypofractionated radiotherapy as compared to 3DCRT (1999 version) and EUD +Tpot, analyzed the EUD in hypofractionated irradiation, different fractionation schedules, and different inter-fraction intervals. The results showed that EUD and especially with Tpot had high sensitivity in showing the influence of cell doubling time on the effects of tumor irradiation, which could have clinical applications.In conclusion, this study suggests that further improvements in the EUD model is needed. In the future, the potential doubling time factor could be considered as a function of total dose, and also include the repair of normal tissues as a factor in the new EUD model.