Normal tissue complication probability (NTCP) calculations as a means to compare proton and photon plans and evaluation of clinical appropriateness of calculated values

Calculation of normal tissue complication probabilities (NTCP) for proton r adiation therapy (PRT) and two photon radiation therapy techniques for cran ial irradiation of childhood optic nerve gliomas was made. Evaluation of us efulness of calculated NTCP values for comparison of treatment plans and cl inical appropriateness of computed data was used. Three radiation plans wer e calculated on datasets of children treated previously for optic nerve gli omas with PRT. Dose-volume histograms (DVH) were computed and used to calcu late NTCP. Evaluated complication endpoints were necrosis, blindness, and c ognitive impairment. Calculated NTCP depended strongly on tumor volume and the normal tissue volume exposed to high radiation doses. Dose conformity a nd steeper dose-gradient correlated with reduced NTCP. Regarding the chosen complication endpoints, PRT was superior to 3D photons; conventional photo ns were calculated to have the highest NTCPs. Differences might reach clini cal significance for cognitive impairment, a frequently observed toxicity. Calculated NTCP values were highly dependent on implemented clinical data. Calculation of NTCP can be used for ranking of treatment plans and modaliti es. Highly dependent on implemented clinical data, the calculated percentag e of NTCP might be more of a figure of merit than a real predictive value a nd requires comparison to clinical experience. Int. J. Cancer (Radiat. Onco l. Invest.) 90, 351-358 (2000). (C) 2000 Wiley-Liss, Inc.