Linear quadratic model compared with TDF and TSD concepts for malignancy of cervix uteri treated with twice daily fractionated schedules.

PURPOSE

Various types of fractionation schemes have been tried in recent year with the objective of improving tumor control rate because conventional fractionation schedules do not always produce optimum results. To compare the radiobiological effectiveness and the gain in the therapeutic ratio due to various fractionation schemes, empirical formulae such as NSD, TDF, CRE and TSD were introduced and used despite of many short comings. Recent linear quadratic (LQ) model is claimed to be able to predict the radiobiological responses of tumor as well as normal tissues more accurately. In the present study various empirical models are compared.

PATIENTS AND METHOD

We treated malignancy of cervix uteri by twice daily fractionation schedules of 1.2 Gy/fraction, 1.4 Gy/fraction and 1.6 Gy/fraction with interfraction interval of four to six hours. The percentage tumor regression was estimated from weekly clinical observations and the TDFt, TSD and ERDt concepts were applied to the data and the predictions are compared.

RESULTS

It was observed that TDFt and TSD concepts predicts equally well (within +/- 3%) the probable tumor regression as predicted by LQ concept.

CONCLUSIONS

Till precise values of various parameters of LQ model are known, the TDF and TSD models can be used to predict probable tumor control rates within reasonable accuracy.