[Computer tomography in determining lung density for irradiation planning]

The paper is concerned with the problems of the determination of lung density in the irradiation planning for thoracic tumors using CT. The mean value of density that was equal to 0.252 +/- 0.118 g/cm3 was obtained proceeding from a study of 118 CT sections of the lungs during quiet breathing. The respective value gets equal to 0.162 +/- 0.022 g/cm3 in deep breathing and 0.282 + 0.050 g/cm3 in full expiration. The values of lung density can vary in different persons. The range of measured values is equal to 0.119 = 0.441 g/cm3 in quiet breathing. The values of lung density vary within the limits of one section from the minimum value in its front part to the maximum one in the rear part. To determine lung densities that are representative for radiation therapy, CT should be performed with a patient breathing quietly in an uninterrupted manner. In significant deviations of density values from those accepted for isodose value calculation, individual consideration of lung density for each person is found appropriate.