Effect of lung inhomogeneity on dose distribution during radiotherapy of patient with lung cancer

Background: presence of inhomogeneities such as lung tissue with lowdensity can perturbs the dose distribution in the path of therapeutic photonbeam and causes undesired cold or hot spots. the aim of this study was toinvestigate the effect of lung tissue inhomogeneities on dose distribution inthorax irradiation. materials and methods: the monte carlo simulation (mc)code of egsnrc-based beamnrc was used to calculate dose distribution for 6mv- siemens primus linear accelerator (linac) in a homogenous phantom.dose perturbation and inhomogeneity corrected factors (icfs) werecalculated due to implementation of lung tissue depended to the lung densityand field size. results: the maximum increased dose in lung tissue with lungdensity of 0.5 and 0.25gr/cm3 was 15.9%, 16.2%, 15.6%, 23.8 %, 24.8% and25.0% for 6 × 6, 10 × 10 and 20 × 20 cm2 field sizes, respectively. themaximum icf for these field sizes was 1.16 and 1.25 for lung density of 0.5and 0.25gr/cm3, respectively. the maximum dose reduction in lung tissuewith density of 0.25 and 0.5gr/cm3 was 19.5% and 4.2 %, and the related icfwas estimated 0.84 and 0.95, respectively. conclusion: involvement of lungtissue in the path of irradiation perturbs the dose distribution which isdependent to the lung density and field size. the icfs resulted from our mcmodel could be useful to accurately calculate the dose distribution inradiotherapy of lung abnormalities.