Dose distribution of narrow beam irradiation for small lung tumor

Purpose : 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. Methods and Materials : 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. Results : 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. Conclusions : 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.