One of the main conclusions of a recently published report by the National Academies of Sciences is that there is no scientific evidence which refutes what is called the "Linear No-Threshold" risk model when dealing with low-level radiation exposure.
What this means regarding risk versus benefit of low-level radiation exposure is that there is an assumption that even very, very low levels of exposure to ionizing radiation carry an associated risk, albeit a small one, of developing cancer as a result of this exposure.
Now to directly address the question regarding the risk versus benefits of medically associated radiation exposure, let's consider some specific examples.
CT scans usually involve the greatest radiation dose to the patient of all the diagnostic radiological procedures. They also, however, often yield the most detailed information to the physician about the nature and extent of the medical condition of the patient. Indeed, CT and MRI scans (which do not involve exposure to ionizing radiation) have revolutionized medicine by allowing doctors to visualize 3-D patient anatomy, including deep-seated organs. The benefits of scans to the patient are obvious, especially in cases where disease processes such as cancer are detected at an early enough stage to treat them more effectively.
Similarly, mammography necessitates the exposure of the breast tissue to a relatively large amount of radiation (about 0.7 millisieverts). If, however, a sub-millimeter sized tumor which could not have been found through self-examination is detected, then most would agree that the additional radiation exposure associated with this procedure, which is about what an international airline flight attendant might receive occupationally in a month, is justified.
Cardiac catheterization procedures, because of their dependence on fluoroscopy to visualize the catheter placement and position, also expose patients to significant radiation doses. Indeed, in some cases the radiation exposure to the patient in a complex catheterization procedure can even exceed that of a CT scan. Few, however, would question the benefit of such procedures to patients in severe cardiac distress.
Radiation oncology is perhaps the most unique medical specialty which uses radiation in that it is used as a therapeutic agent rather than a diagnostic tool. The fact that radiation, which is known to cause cancer in humans in certain cases, can also be used to treat cancer is a paradox to many. Its effectiveness stems from the fact that malignant cells are not able to repair radiation changes as compared to normal body cells. Therefore, a radiation dose that a normal cell could tolerate will kill a cancer cell.
Today, radiation oncology procedures such as external beam radiotherapy, iodine-125 prostate seed implants and the revolutionary new type of radiotherapy known as intensity modulated radiation therapy (IMRT) provide very effective and relatively non-invasive weapons in the ongoing fight against cancer. Although it is always a possibility that a secondary cancer could result from therapeutic exposure, it is relatively rare and seen as a very reasonable risk for patients fighting what is often a life-threatening disease.
In all cases where medical procedures involving radiation exposure to the patient are proposed, it is the right and responsibility of the patient to question the necessity of the procedure, and the benefit versus the risk of the exposure. It is also the responsibility of all physicians who prescribe radiation related procedures to do so with discretion, and only in cases where the benefit to the patient clearly outweighs the associated radiation risks.
Charles Wild is a physicist in the Radiation Oncology Department at Mount Nittany Medical Center.