Choose one of the following concepts: time, distance or shielding and give an example of a situation in which the time, distance or shielding is beneficial in limiting dose. Explain the concept behind the example that you choose to give.
One of the very first things we learned in our radiation therapy program was the concept of ALARA (As Low As Reasonably Achievable) and how time, distance, and shielding each play a significant role in the safety of both the radiation oncology staff and patients. For this week's topic I have decided to discuss distance.
By increasing the distance between the radiation source and the person being irradiated you decrease the amount of radiation dose they will receive. Because X-rays diverge from the center of the beam, the intensity of the radiation spreads out and thus decreases the further away from the source you are. The Inverse Square Law is used to demonstrate the inversely proportional relationship between distance and radiation intensity and uses the equation, Intensity1 / Intensity2 = (Distance2 / Distance1 )squared.[1] For example, using the inverse square equation, if the intensity of the beam measured 1,000 mR at a distance of 40 inches away from an X-ray tube then at a distance of 72 inches the intensity would measure 308 mR.
Distance is taken into account when handling brachytherapy seeds and sources. Forceps are used when handling seeds which increases the distance between the seeds and the handler, thus decreasing the amount of radiation the handler is exposed to. In addition to the use of forceps the amount of time seeds are handled is minimized as much as possible which in turn results in a decreased amount of exposure.
Reference:
1. Washington CM, Leaver D. Principles and Practice of Radiation Therapy. 3rd ed. St. Louis, MO: Mosby-Elsevier; 2010:115.
By increasing the distance between the radiation source and the person being irradiated you decrease the amount of radiation dose they will receive. Because X-rays diverge from the center of the beam, the intensity of the radiation spreads out and thus decreases the further away from the source you are. The Inverse Square Law is used to demonstrate the inversely proportional relationship between distance and radiation intensity and uses the equation, Intensity1 / Intensity2 = (Distance2 / Distance1 )squared.[1] For example, using the inverse square equation, if the intensity of the beam measured 1,000 mR at a distance of 40 inches away from an X-ray tube then at a distance of 72 inches the intensity would measure 308 mR.
Distance is taken into account when handling brachytherapy seeds and sources. Forceps are used when handling seeds which increases the distance between the seeds and the handler, thus decreasing the amount of radiation the handler is exposed to. In addition to the use of forceps the amount of time seeds are handled is minimized as much as possible which in turn results in a decreased amount of exposure.
Reference:
1. Washington CM, Leaver D. Principles and Practice of Radiation Therapy. 3rd ed. St. Louis, MO: Mosby-Elsevier; 2010:115.