Repopulation of Tumour Cells during Radiotherapy Is Doubled during Treatment Gaps

The aim of this work is to analyse the proliferation of tumour cells in the treatment gap during the radiotherapy for head neck cancer. Material and Methods The clinical material is based on records of head and neck patients treated by radiotherapy alone in our institution. The effect of radiotherapy was assumed to be described by a linearquadratic model. The patient data were fitted directly to the radiobiological model and the parameters were estimated using maximum-likelihood procedures. Results According to our model results of treatment were significantly correlated with Normalised Total Dose of radiation, the tumour progression (according to TNM), the overall treatment time and the gap duration. The laryngeal cancers had better prognosis then cancers of oroand nasopharynx. When the treatment time is prolonged without treatment interruptions 0.36 Gylday is lost due to the repopulation of tumour cells. During the treatment gap proliferation is faster and 0.67 Gylday is lost. Conclusion Proliferation of tumour cells is faster during the treatment gap then during the days with irradiation.