Dose distribution of narrow beam irradiation for small lung tumor.

Abstract

To aid in the selection of incident X-ray energy for stereotactic irradiation (STI) of lung tumor, dose distribution was investigated in a model of a thorax embedded with a tumor. The dose distribution in a thorax model was calculated using the EGS4 Monte Carlo simulation; it was also measured with dosimetric film of a tentative thorax phantom. Uniformity of dose distribution in a tumor region was compared among the results of irradiation for several X-ray energies, and optimal X-ray energy for STI of a lung tumor was discussed. Dose distributions in the thorax were obtained. An increase in X-ray energy led not only to an increased dose delivered to the tumor, but also to an increased dose to surrounding normal lung tissue. The flat range in dose distribution along the beam axis and in the beam profiles of the tumor increases with decreasing X-ray energy. Consequently, lower energy, rather than higher energy, is recommended for STI of a lung tumor in terms of higher uniformity in the target volume.