Evaluation of Lung Density and Its Dosimetric Impact on Lung Cancer Radiotherapy: A Simulation Study

Background: The dosimetric parameters required in lung cancer radiation therapy are taken from a homogeneous water phantom; however, during treatment, the expected results are being affected because of its inhomogeneity. Therefore, it becomes necessary to quantify these deviations.Objective: The present study has been undertaken to find out inter- and intra- lung density variations and its dosimetric impact on lung cancer radiotherapy using Monte Carlo code FLUKA and PBC algorithms.Material and Methods: Density of ۱۰۰ lungs was recorded from their CT images along with age. Then, after PDD calculated by FLUKA MC Code and PBC algorithm for virtual phantom having density ۰.۲ gm/cm۳ and ۰.۴ gm/cm۳ (density range obtained from CT images of ۱۰۰ lungs) using Co-۶۰ ۱۰ x۱۰ cm۲ beams were compared.Results: Average left and right lung densities were ۰.۲۷۵±۰.۳۸۷ and ۰.۲۷۰±۰.۳۸۳ respectively. The deviation in PBC calculated PDD were (+)۲۱۶%, (+۹۱%), (+)۴۵%, (+)۲۶.۸۸%, (+)۱۴%, (-)۱%, (+)۲%, (-)۰.۴%, (-)۱%, (+)۱%, (+)۴%, (+)۴.۵% for ۰.۴ gm/cm۳ and (+)۳۱۱%, (+)۱۷۷%, (+)۱۱۸%, (+)۹۰.۹۵%, (+)۷۲.۲۳%, (+)۵۵.۸۳% ,(+)۳۸.۸۵%, (+)۲۸.۸۰%, (+)۲۱.۷۹%, (+)۱۵.۹۵%, (+)۱.۶۷%, (-) ۲.۱۳%, (+)۱.۲۷%, (+)۰.۳۵%, (-)۱.۷۹%, (-)۲.۷۵% for ۰.۲ gm/cm۳ density mediums at depths of ۱mm, ۲mm, ۳mm, ۴mm, ۵mm, ۶ mm, ۷ mm, ۸mm, ۹mm,۱۰mm, ۱۵mm, ۳۰mm, ۴۰mm, ۵۰mm, ۸۰mm and ۱۰۰ mm, respectively.Conclusion: Large variations in inter- and intra- lung density were recorded. PBC overestimated the dose at air/lung interface as well as inside lung. The results of Monte Carlo simulation can be used to assess the performance of other treatment planning systems used in lung cancer radiotherapy.

کلیدواژه ها:

PBC ، Monte Carlo Code FLUKA ، Variation in Lung Density ، Virtual Phantom ، Computed Tomography