[Studies of lung density as a basis for irradiation planning]

The irradiation of tumors in thoracal area presupposes an exact irradiation planning including the lung to prevent therapy limiting dosage errors. With it the exact dimension and the density of the lung have to be known. It was investigated of which factors the lung density depends on and how they affect the dosage precision. Within the lung the density fluctuates considerably; these fluctuations are different from patient to patient and depend on age among other things. This age dependence can be represented by a regression straight line; with this the lung density of patients can be found out from age approximatively. Individual investigation of density from CT-sections can improve precision of dose calculation up to 4%. It has to pay attention to producing CT-sections with normal respiration and in such position as the later irradiation shall be done in.