Answer to Question #12761 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I have searched and researched everywhere to try to find information I can understand. What I want is a more layman explanation of the following information provided regarding a radiation therapy treatment: 66 Gy/60 Gy54Gy in 30 Fractions.
The 66 Gy, 60 Gy, and 54 Gy are radiation doses to areas being treated. A Gray (Gy) is a unit of radiation dose, called the "absorbed dose." Absorbed dose is the amount of energy from the radiation that is absorbed by whatever matter the radiation is going through. One Gy is equal to 1 Joule (J) of energy absorbed in 1 kg of matter; in this case, the matter is the tumor being treated. (For reference, 1 J is equal to the amount of energy used by a 40-watt lightbulb in 0.025 seconds.)
What you provided is the prescription for the radiation therapy. This prescription calls for the major tumor area to receive 66 Gy, while areas with microscopic disease or areas near critical structures, such as the spinal cord, will receive the lower doses of 60 Gy and 54 Gy. This technique is sometimes called "dose painting."
These doses will not be delivered all at once, but will be spread over a period of six weeks/30 fractions. This is a common radiation therapy technique called fractionating the dose. On each day of treatment only a fraction of the total dose (in fact, 1/30 of the total dose) to each area will be delivered. Each day of treatment is called a fraction. So, for example, the major tumor area will receive a radiation dose of 2.2 Gy per fraction or day.
If you have specific questions, the best people to consult would be your radiation oncologist, medical physicist or therapist providing treatment.
Jacqueline Emrich, PhD, DABR
Kent Lambert, CHP, FHPS