Mendes Bruno Melo, Trindade Bruno Machado, Fonseca Telma Cristina Ferreira, de Campos Tarcisio Passos Ribeiro
1 Programa de Ciências e Técnicas Nucleares - Departamento de Engenharia Nuclear, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
2 Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN), Seção de Dosimetria das Radiações, Belo Horizonte, Brazil.
Br J Radiol. 2017 Dec;90(1080):20170187. doi: 10.1259/bjr.20170187. Epub 2017 Oct 27.
The aim of this work was to simulate a 6MV conventional breast 3D conformational radiation therapy (3D-CRT) with physical wedges (50 Gy/25#) in the left breast, calculate the mean absorbed dose in the body organs using robust models and computational tools and estimate the secondary cancer-incidence risk to the Brazilian population.
The VW female phantom was used in the simulations. Planning target volume (PTV) was defined in the left breast. The 6MV parallel-opposed fields breast-radiotherapy (RT) protocol was simulated with MCNPx code. The absorbed doses were evaluated in all the organs. The secondary cancer-incidence risk induced by radiotherapy was calculated for different age groups according to the BEIR VII methodology.
RT quality indexes indicated that the protocol was properly simulated. Significant absorbed dose values in red bone marrow, RBM (0.8 Gy) and stomach (0.6 Gy) were observed. The contralateral breast presented the highest risk of incidence of a secondary cancer followed by leukaemia, lung and stomach. The risk of a secondary cancer-incidence by breast-RT, for the Brazilian population, ranged between 2.2-1.7% and 0.6-0.4%.
RBM and stomach, usually not considered as OAR, presented high second cancer incidence risks of 0.5-0.3% and 0.4-0.1%, respectively. This study may be helpful for breast-RT risk/benefit assessment. Advances in knowledge: MCNPX-dosimetry was able to provide the scatter radiation and dose for all body organs in conventional breast-RT. It was found a relevant risk up to 2.2% of induced-cancer from breast-RT, considering the whole thorax organs and Brazilian cancer-incidence.
本研究旨在模拟左侧乳房采用物理楔形板（50 Gy/25次）的6MV常规乳房三维适形放射治疗（3D-CRT），使用稳健模型和计算工具计算身体器官的平均吸收剂量，并估计巴西人群的继发癌症发病风险。
模拟中使用VW女性体模。在左侧乳房定义计划靶区（PTV）。采用MCNPx代码模拟6MV平行相对野乳房放射治疗（RT）方案。评估所有器官的吸收剂量。根据BEIR VII方法计算不同年龄组放疗诱发的继发癌症发病风险。
RT质量指标表明方案模拟正确。观察到红骨髓（RBM）和胃的吸收剂量值较高（分别为0.8 Gy和0.6 Gy）。对侧乳房继发癌症发病风险最高，其次是白血病、肺癌和胃癌。巴西人群因乳房RT导致的继发癌症发病风险在2.2%-1.7%和0.6%-0.4%之间。
通常不被视为危及器官（OAR）的RBM和胃，继发癌症发病风险分别高达0.5%-0.3%和0.4%-0.1%。本研究可能有助于乳房RT的风险/效益评估。知识进展：MCNPX剂量测定法能够为常规乳房RT中的所有身体器官提供散射辐射和剂量。考虑整个胸部器官和巴西癌症发病率，发现乳房RT诱发癌症的相关风险高达2.2%。
