RESUMO
In this work the head and neck cancer treatment of a pregnant patient was experimentally simulated. A female anthropomorphic Alderson phantom was used and the absorbed dose to the fetus was evaluated protecting the patient's abdomen with a 7cm lead layer and using no abdomen shielding. The target volume dose was 50Gy. The fetus doses evaluated with and without the lead shielding were, respectively, 0.52±0.039 and 0.88±0.052cGy.
Assuntos
Feto/efeitos da radiação , Neoplasias de Cabeça e Pescoço/complicações , Neoplasias de Cabeça e Pescoço/radioterapia , Complicações Neoplásicas na Gravidez/radioterapia , Simulação por Computador , Feminino , Humanos , Imagens de Fantasmas , Gravidez , Proteção Radiológica/instrumentação , Dosagem Radioterapêutica , Dosimetria TermoluminescenteRESUMO
An increasing number of studies have shown that post-mastectomy radiotherapy presents benefits associated with the patients survival and a significant fraction of the treated patients makes use of tissue expanders for breast reconstruction. Some models of tissue expanders have a magnetic disk on their surface that constitutes heterogeneity in the radiation field, which can affect the dose distribution during the radiotherapy treatment. In this study, the influence of a metallic heterogeneity positioned in a breast tissue expander was evaluated by means of Monte Carlo simulations using the MCNPX code and using Eclipse treatment planning system. Deposited energy values were calculated in structures which have clinical importance for the treatment. Additionally, the effect in the absorbed energy due to backscattering and attenuation of the incident beam caused by the heterogeneity, as well as due to the expansion of the prosthesis, was evaluated in target structures for a 6 MV photon beam by simulations. The dose distributions for a breast treatment were calculated using a convolution/superposition algorithm from the Eclipse treatment planning system. When compared with the smallest breast expander volume, underdosage of 7% was found for the largest volume of breast implant, in the case of frontal irradiation of the chest wall, by Monte Carlo simulations. No significant changes were found in dose distributions for the presence of the heterogeneity during the treatment planning of irradiation with an opposed pair of beams. Even considering the limitation of the treatment planning system, the results obtained with its use confirm those ones found by Monte Carlo simulations for a tangent beam irradiation. The presence of a heterogeneity didn't alters the dose distributions on treatment structures. The underdosage of 7% observed with Monte Carlo simulations were found for irradiation at 0°, not used frequently in a clinical routine.
Assuntos
Neoplasias da Mama/radioterapia , Neoplasias da Mama/cirurgia , Mastectomia/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Dispositivos para Expansão de Tecidos , Feminino , Humanos , Mamoplastia/métodos , Método de Monte Carlo , Imagens de Fantasmas , Fótons , Radioterapia (Especialidade) , Dosagem RadioterapêuticaRESUMO
In the radiotherapy treatment planning of a lesion located in the head region with small field radiation beams, the heterogeneity corrections play an important role. In this work, we investigated the influence of a bony heterogeneity on dose profile inside a soft tissue phantom containing a bony material. PDD curves were obtained by simulation using the Monte Carlo code EGSnrc and employing Eclipse(R) treatment planning system algorithms (Batho, Modified Batho, Equivalent TAR and Anisotropic Analytic Algorithm) for a 15 MV photon beam and field sizes of 2x2 and 10x10 cm(2). The Equivalent TAR method exhibited better agreement with Monte Carlo simulations for the 2x2 cm(2) field size. The magnitude of the effect on PDD due to the bony heterogeneity for 1x1, 2x2 and 10x10 cm(2) field sizes increases to 10, 5 and 3%, respectively.