Klin Onkol 2020; 33(Suppl 1): 31-37. DOI: 10.14735/amko2020S31.
Background: Re-irradiation, in combination with systemic and biological therapy in recent years, has become a meaningful option for locally recurrent cancers and for in-field second malignancies in cases where surgical salvage is not feasible. The development of imaging techniques and their applications in radiotherapy have created a space for the development of procedures and, by means of radiobiological modelling, for the estimation of the residual/additional tolerance doses for organs at risk (OaR) during re-irradiation. Normal tissues and organs can regenerate and repair their damage after initial radiotherapy. However, residual tolerance doses of OaR are considerably different. In the tissues with early response, a complete restoration occurs almost within a couple of months so that the second series of the exposure could be applied in almost the same amount. In the tissues and organs with the late response, the extent of the damage depends on several parameters: a total dose from the initial therapy, a structure of the sub-functional units of the tissue and an interval between the series. Strong recovery takes place in 3–6 months in case of the skin, mucosa, spinal cord and lung. Other tissue, e. g. kidneys, heart or bladder, dispose with a small regenerative capacity only. Purpose: The article provides an overview about the cumulative values of the biological effective dose (BEDcum) on organs-at-risk (OaR) obtained from retrospective studies and description of the original model for the determination of the residual tolerance dose implemented to calculating normal tissue complication probability (NTCP) from the individual treatment plans by means of the own-made program „BioGray".
