Basic Principles of Radiation
Radiation therapy uses ionizing radiation in the treatment of patients with both benign and malignant diseases.
Radiation therapy is considered a local treatment because cells are being destroyed only in the area being treated (Haas, 2004).
The dose of radiation therapy is determined by several factors (Haas, 2004).
- Radiosensitivity of the tumor
- Normal tissue tolerance
- Volume of tissue to be irradiated
The gray (Gy) has replaced the rad (radiation absorbed dose) as the accepted term for radiation dosage. To summarize, 1 Gray (Gy) = 100 rads;1 cGy = 1 rad (Haas, 2004).
For radiation following breast-conserving surgery, the typical daily dose is 180–200 cGy delivered five days a week over a 4.5- to 5-week period. The daily dose usually is called a fraction (Dow, 2006).
For some tumors, including breast tumors, a boost of radiation is administered to complete the course of treatment. A boost is delivered to a limited area within the treatment field that is at greater risk of recurrence. For breast cancer, this is usually at or near the lumpectomy site (Haas, 2004).
A boost dose to the primary tumor site takes an additional five to eight daily fractions of 200 cGy.
Dow, K.H. (2006). A pocket guide to breast cancer (3rd ed.). Sudbury, MA: Jones and Bartlett.
Haas, M. (2004). Radiation therapy. In C.G. Varricchio (Ed.). A cancer source book for nurses (8th ed., pp. 131–147). Sudbury, MA: Jones and Bartlett.