When radiation therapy is used to kill cancerous cells in the body, it is important to measure the dose correctly to avoid unnecessary damage to normal cells in the body.
Radiation is not selective to tumor cells and therefore targets any cells that are in the process of replication when the therapy is applied. This thereby stresses the importance of administering the correct dose in order to ensure optimal efficiency with minimal side effects.
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Standard dose
Gray (Gy) is the unit used to measure the total amount of radiation that the patient is exposed to. This can also be recorded as centigray (cGy), which is 0.01 of a single Gy unit.
Adjuvant therapy doses typically range from 45 to 60 Gy for the treatment of breast, head, and neck cancers. Typically, these doses are divided into multiple smaller doses that are given over a period of one to two months. The specific dose for each patient depends on the location and severity of the tumor. The dose determination is therefore at the discretion of the radiation oncologist who is responsible for such therapeutic decisions.
Dose fractioning
The total radiation dose is usually divided into several fractions. For most patients who require radiation therapy, the total dose is broken up into daily doses of five times a week for a total period of five to eight weeks. Some cancers, however, require treatment more often than once per day.
Each fraction will contain a small amount of radiation that gradually accumulates to form the total dose. This technique allows the cancerous cells to be treated effectively, whilst reducing the amount of damage the treatment can cause to normal tissues.
Dose frequency
Hyperfractionated radiation divides the daily dose into two treatments each day, which means that the patient is subjected to smaller but more frequent doses of radiation over the same period of time.
Conversely, hypofractionated radiation breaks the total dose into larger doses, often giving a dose less than once each day.
What to Expect When Receiving Radiation Therapy Treatment
Treatment length
Standard treatment with radiation therapy lasts for five to eight weeks, depending on the specific type of cancer being treated, and is at the discretion of the oncologist supervising the therapy.
Accelerated radiation refers to when the total dose is administered over a shorter period of time than usual. This involves more frequent doses, usually more often than once daily, to administer the equivalent total dose over a shorter period of time. This can be useful in some types of cancer that require a more aggressive treatment regimen.
Changes in the dose frequency and treatment length do not alter the total exposure to radiation and, as a result, the long-term effects remain similar. However, different treatment fractioning and accelerated treatments are often associated with a faster onset of effects, both on normal and cancerous cells.
Patient positioning during treatment
The exact position of the patient during the radiation treatment is of utmost importance to ensure that the correct dose of radiation is emitted to the intended area of the body.
It is common practice for skin to be marked to indicate where the treatment should be focused. The patient should be instructed to remain in the same position without moving for the entire duration of each treatment fraction.
A mold or cast can be helpful to assist patients in maintaining the correct position while radiation therapy is in progress. Additionally, areas of the body that do not contain tumor cells should be subjected to as little radiation as possible, often necessitating blocks or shields to protect other parts of the body.
References
Further Reading
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