Use of radiation in medicine
Since the use of radiation may cause harm in addition to benefits, physicians must consider the necessity of radiological examinations, interventional procedures or radiotherapy on a case-by-case basis. These considerations will also take into account any previous examinations performed. X-ray examinations, nuclear medicine examinations, image guided interventional procedures and radiotherapy always require a referral by a physician. When an examination is performed, the radiation dose is kept as low as possible, but still sufficient for the purpose of the examination or interventional procedure. Radiotherapy uses a sufficient amount of radiation to achieve the desired result while minimizing the radiation received by healthy tissues.
X-ray and nuclear medicine examinations
The radiation dose caused to the patient depends both on the examined or treated part of the body and the examination method used. The lowest doses occur in X-ray imaging of the teeth, limbs and lungs. The radiation dose from conventional X-ray examinations of these parts of the body corresponds to the dose received from background radiation in about one or two days. Correspondingly, the radiation dose from a more extensive examination of the lungs and from various X-ray examinations of the spine corresponds to a background radiation dose received over the course of a few days or even up to 2–3 months.
Computed tomography (CT) scans provide more accurate three-dimensional images, but they also cause a higher radiation dose. The resulting radiation dose corresponds to a background radiation dose of a few months or several years. Cone beam computed tomography (CBCT) scans lie between a conventional X-ray examination and a CT scan in terms of resolution and radiation dose.
The radiation dose caused by nuclear medicine examinations depends on the radiopharmaceutical and on the CT scan that may accompany the examination. The dose can range from one month to up to several years of background radiation exposure.
The dose caused by background radiation and medical examinations varies typically, by more than 30%. The unit that performed the examination can inform the patient on the level of exposure caused by a particular examination.
How can patient exposure be optimised?
Examinations that cause radiation exposure can be optimised for each individual patient when the attending physician describes the patient's situation and clinical issues in the referral with sufficient detail. In X-ray examinations, it is important to limit the area to be imaged. The area to be imaged should not be too large but should cover everything that is essential for the purpose of the examination. The imaging parameters of the device also affect both the image quality and the radiation dose to the patient. The desired image quality may vary a lot from case to case. The rule of thumb is that the higher the image resolution, the higher the radiation exposure to the patient. On the other hand, a high-resolution image provides more detailed information for diagnostic purposes.
Shielding the patient with wearable radiation shields reduces the dose relatively little compared to the principles described above. Using radiation shields also poses a risk of an increased dose if the shield intrudes into the area being imaged, necessitating a re-scan.
Releasing a patient after a nuclear medicine examination or therapy
Nuclear medicine examinations typically use relatively small amounts of short-lived radioisotopes. In these cases, the patient can be released after the examination without any special restrictions. By contrast, the activities used in radionuclide therapy are higher and the radioisotopes are longer-lived. These patients and their excretions might radiate for some time after the therapy has been administered. If the patient has been treated with a radiopharmaceutical preparation that emits high levels of gamma radiation, the patient often has to stay in the hospital for 1–3 days until the amount of the radioisotope in the body has fallen sufficiently. The patient can be relased when the hospital considers that the radiation exposure caused by the radiating patient to other people is low enough.
The patient’s radiation dose in radiotherapy
Radiotherapy uses radiation to deliberately destroy cancer cells. Therefore, the radiation doses used in radiotherapy are significantly higher than in X-ray or nuclear medicine examinations. In order to minimize its adverse effects, radiotherapy is administered sequentially over the course of several treatment sessions and is targeted precisely to the desired area. The doses used in radiotherapy are very high and almost all patients experience mild, transient side effects. However, long-term adverse effects from radiation are rare.