The space radiation environment is composed of ionizing particles that may pose health risks to crew members during Low Earth Orbit (LEO) and deep space missions. NASA has established astronaut career radiation limits for cancer of 3% Risk of Exposure Induced Death (REID) at the 95% confidence level. The REID is the increased lifetime risk of death from cancer due to radiation exposure in comparison to an unexposed background population and has been traditionally mitigated by passive shielding design concepts and limiting safe days in space. Additional reduction in radiation exposure risk may be achieved with Medical Countermeasures (MCM). Recent meta-analyses have demonstrated the efficacy of aspirin in the reduction of the background colorectal cancer incidence and mortality rates for specific cohorts. Additional studies of warfarin in patients greater than 50 years of age have indicated statistically significant decreases in stomach, bladder, brain, prostate, and lung cancer incidence as compared to control groups. While ultimate selection of suitable countermeasures will be the responsibility of flight surgeons, this paper presents a general methodology for incorporating MCM into the NASA Space Radiation Cancer Risk model and includes modifications of the background mortality rates (hazard rates) and the radiation risk coefficients to numerically quantify the benefits of MCM. As examples of the method, aspirin and warfarin will be employed as MCM in a sensitivity analysis to compute the REID for astronauts embarking on a one-year deep space mission scenario.

空间辐射环境由电离粒子组成，这些粒子可能在低地球轨道（LEO）和深空任务中对机组人员构成健康风险。美国国家航空航天局（NASA）制定了95％置信水平下的3％暴露诱发死亡风险（REID）的航天员职业癌症辐射限额。与未暴露的背景人群相比，REID是由于暴露于辐射而导致癌症死亡的终生风险增加，并且传统上已通过被动屏蔽设计概念和限制太空安全天数来缓解。使用医疗对策（MCM）可以进一步降低辐射暴露风险。最近的荟萃分析已证明阿司匹林在降低特定人群的背景大肠癌发病率和死亡率方面的功效。华法林在50岁以上患者中的其他研究表明，与对照组相比，胃癌，膀胱癌，脑癌，前列腺癌和肺癌的发生率有统计学意义的降低。尽管最终选择合适的对策将是飞行外科医生的责任，但本文提出了将MCM纳入NASA空间辐射癌症风险模型的一般方法，并包括对背景死亡率（危险率）和辐射风险系数进行数值修正。量化MCM的好处。作为该方法的示例，将在敏感性分析中使用阿司匹林和华法林作为MCM，为即将进行一年深空任务的宇航员计算REID。