A study of the effect of the lung shape on the lung absorbed dose in six standard photon and neutron exposure geometries

According to the published results of radiation dosimetry studies, there are significant discrepancies in the organ absorbed doses of existing adult male phantoms. As stated, differences in the organ absorbed doses may be associated with the variations in the organs’ volumes, shapes and positions in the body frame. Therefore, this paper focuses on the effect of the lung shape on the lung absorbed dose by creating a series of voxel phantoms, in which the lung shape follows a statistical distribution. These phantoms were exposed to mono-energetic photons and neutrons in six standard irradiation geometries. The results show that when the phantom is irradiated by the low-energy photons, the effects of the lung shape on the lung absorbed dose are considerable (with an uncertainty of more than 100%). For the other irradiation conditions, the variation in the lung shape causes an uncertainty of less than 10% in the dose delivered to the lung

Dose calculation of different eye substructures using a realistic eye model when treating ocular tumors with electron therapy

One of the most frequent types of intraocular melanoma in adults is choroidal uveal melanoma. The most commonly used forms of radiation therapy are ophthalmic plaque brachytherapy and charged particle external radiation therapy. In the absence of adequate facilities for brachytherapy and proton therapy, electron therapy would be an efficient radiation therapy technique for treating eye melanomas. In the present work, the Monte Carlo code MCNPX 2.6.0 was used to calculate the dose distribution to substructures of the eye in electron therapy of three common choroidal tumors. The simulations were performed for 6 electron beams with nominal energies between 5 MeV and 10 MeV and also for 10 incidence angles. To identify suitable treatment plans, the tumor-to-sensitive zone dose ratios were estimated. Moreover, the equivalent doses delivered to healthy substructures of the eye were also calculated. The results indicate that for the treatment of tumors located at the posterior part of the eye, an electron beam with energy of 10 MeV and incident angle of 45° relative to the eye axis provides the best tumor coverage while optimally sparing other eye substructures. In addition, for tumors positioned on the upper and lower parts of the vitreous, electron beams with energy of 10 MeV, an azimuthal angle of 270°, and polar incident angles of 90° and 105°, respectively, lead to appropriate dose delivery