Radiation oncologist   
A medical doctor specializing in the treatment of cancer with radiation.

Radiation pneumonitis   
Inflammation in the lung that sometimes results from the radiation therapy beam.

Radiation recall   
The reoccurrence of a side effect of radiation treatments (such as skin irritation) long after the radiation therapy has been completed.

Radiation therapist   
A specially trained technician who administers radiation treatments.

Radiation therapy   
Radiation therapy uses high-energy x-rays, either beamed from a machine or emitted by sources implanted in a body part, to kill cancer cells.

Radical mastectomy   
Removal of the entire breast along with under-lying muscle and lymph nodes of the armpit.

Radioactive   
Emitting energy in the form of waves or particles.

Radioactive seeds   
Small pellets of radioactive material that can be placed down a catheter positioned in an organ of the body.

Radiologist   
A doctor who specializes in the use of x-rays to diagnose and treat disease.

Radon   
A naturally occurring gas originating from the ground that when inhaled is associated with increased rates of lung cancer development.

Randomization   
A method used to prevent bias in research. People are assigned by chance, often by a computer, either to receive the study agent (intervention group) or not (control group).

Recurrence:    
The reappearance of cancer after a period of remission.

Red blood cells (Erythrocyte)    
Cells in the blood that bring oxygen to tissues and take carbon dioxide from them.

Red blood count    (RBC)
The number of red blood cells seen in the blood sample.

Regression   
The shrinkage of cancer growth.

Relapse   
The reappearance of cancer.

Remission   
Complete or partial disappearance of the signs and symptoms of disease.

Resectable   
The finding that a cancer does not grow into any vital structure and can therefore be removed by a surgical procedure.

Risk factor   
Anything that increases a person’s chance of developing cancer, e.g., smoking.