Equivalent dose calculation in simulation of lung cancer treatment and analysis of dose distribution profile.

Currently, lung cancer is one of the most lethal types of cancer (IARC, 2012), the pathology being detected in advanced stage, when the tumor has considerable volume because the disease in most cases asymptomatic in the early stages (INCA, 2016). Dosimetry analysis of healthy organs under real conditions is not feasible. Therefore, computational simulations are used to aid in dose verification in organs of patients submitted to radiotherapy. The goal of this study was to calculate the equivalent dose, due to photons, in the surrounding of healthy organs of patients submitted to radiotherapy for lung cancer, through computational modeling. The simulation was performed using the MCNPX code (MNCPX, 2006), Rex and Regina phantoms (ICRP 110, 2009), radiotherapy room, Siemens Oncor Expression accelerator operating at 6 MV and treatment protocol adopted at the INCA (National Cancer Institute - Brazil). The results obtained, considering the dose due to photons for both phantoms indicate that organs located inside the thoracic cavity received higher dose, being the bronchi, heart and esophagus more affected, due to their anatomical positioning. Clinical data describe the development of bronchiolitis, esophagitis and cardiomyopathies with decreased cardiopulmonary function as one of the major effects of lung cancer treatment. In the Regina phantom, the second largest dose was in the region of the breasts with 615.73 mSv/Gy, while in the Rex the dose was 514.06 mSv/Gy, event related to the difference of anatomical structure of the organ. A qualitative analysis was performed between the dose deposition profile of the treatment planning system and the simulated treatment through the tmesh command and a similar profile of dose distribution was verified throughout the patient's body.