Implications of lung corrections for dose specification in radiotherapy.

The influence of taking into account the lung density in the calculation of the dose distributions was examined for a group of 23 patients with bronchus carcinoma. Anatomical information and electron densities were available by means of CT scans. All calculations were made for cobalt-60 gamma rays using a patient specific multiple field irradiation technique. The effect of lung tissues for the dose distributions was calculated using a generalization of Batho's method. All patients entered into this study were planned to receive a minimum tumor dose of 60 Gy, calculated without correction for lung density. The actual dose in each patient was recalculated with lung correction. In the group of patients the corrected minimum tumor dose varied between 63 Gy and 77 Gy (105-128%). The calculated homogeneity of the dose in the target area and the dose to surrounding normal tissues are also affected by lung correction. For different radiation techniques and different methods of dose specification, the interrelation between corrected and uncorrected dose is presented in tables. The impact of lung correction on the uncorrected dose schedules that are commonly used in the treatment of patients with lung cancer is discussed.