The Future of Radiological Protection

We propose the Sea Saw (SS) model, which provides a unified description of the biological effect caused by radiation. This can be directly applied to clinic plans in radiotherapy and the basic formula for radioprotection. This can be replaced by the so-called LNT or LQM bases to describe the effects caused by radiation exposure and we can estimate exactly the effects of fractionation cases or we can directly take account of dose rate effect without any additional DDREF. This can be done by introducing the cell exclusion effect. The model is very simple and intuitively acceptable by expressing the dose-rate effect and can be easily extended to the radiation clinic cases and overcomes the difficulties of the standard method using LQM based BED. The calculated result of our model reproduces the existing data of the time dependence of the cancer volume during the cancer treatment measurement. We demonstrate that different initial volumes, namely for the cases where irradiation starts with a smaller initial volume is more effective than a larger volume. Especially if the cancer volume is almost full in the tissue, the radiation effect of the cancer treatment is very small. On the other hand, for the smaller initial volume, the cancer treatment is found to work more effectively to reduce the cancer volume. Using this model we can predict the time dependence of the cancer volume, and clarify how the effect of radiation therapy depends on the cancer stage on the starting time of the radiation treatment.

After explaining the essential difference between our SS model and traditional LQ treatment with BED index, we would like to report the results of SS model by displaying the comparison of our prediction of the estimated results with the relevant new data from the radiation therapy sectional group of Osaka International and will report the comparison those with our prediction. We can also consider continuous but time-dependent irradiation cases and got interesting outcomes on the time dependence of the tumor volume for various clinic plans. Especially by choosing the value of the dose rate to be balanced with the total growth rate, the tumor volume is kept constant.

Finally, I would like to emphasize that our SS model leads us not only with a unified description of radiation therapy but also indicates the misleading principle based on LNT or LQM hypothesis which is still adopted in the society of radiation protection.

Keywords: SeaSaw model; LNT; LQM; radiation clinic; radiation protection