Patient radiation dose management: Rad Tech

The radiation dose a patient receives depends on the examination, the anatomy and size of the patient, the equipment, and the imaging technique. Because of this, there are several different ways to describe patient radiation dose. Each dose quantity answers a different question and helps imaging professionals evaluate and manage exposure while maintaining diagnostic image quality.

Now, the way patient dose is described depends partly on the imaging procedure. For general radiography and fluoroscopy, patient radiation dose can be described using entrance skin exposure, or ESE, which describes radiation exposure at the patient’s skin surface, where the x-ray beam enters the body. Other descriptions include mean marrow dose, or MMD, which estimates the average absorbed dose to active bone marrow; the genetically significant dose, or GSD, which is a historical, population-level estimate of gonadal exposure and its possible effect on future generations. And tissue dose, which describes absorbed dose to a specific organ or tissue.

In addition, air kerma describes the radiation energy transferred to air; and dose-area product, or DAP, combines air kerma with the area of the x-ray field, so it reflects both radiation output and the amount of tissue that’s irradiated.

With CTs, scanner output is commonly reported using the volume computed tomography dose index, or CTDIvol. CTDIvol is calculated from radiation measurements made in standardized test objects that represent general head and body sizes. Because these measurements are made in test objects rather than in the patient, CTDIvol represents scanner output rather than the exact dose absorbed by an individual patient.

Finally, dose-length product, or DLP, combines CTDIvol with the length of the scanned region.

Across all these imaging modalities, effective dose is measured in millisieverts, or mSv. It estimates the potential for long-term chance-based effects, called stochastic effects, by considering which tissues are exposed and how radiosensitive they are. Effective dose estimates overall stochastic risk by weighting exposed tissues according to radiosensitivity.

An important safety goal for radiologic technologists is to keep radiation exposure as low as reasonably achievable, or ALARA, while still obtaining the diagnostic information needed for patient care. Unlike occupational exposure, patient exposure is managed through justification and optimization rather than a fixed dose limit. Instead, ALARA is applied mainly through two connected principles: justification and optimization.

Part of ALARA is avoiding unnecessary examinations and ensuring that an examination is clinically justified. An examination using ionizing radiation should be performed only when there’s an appropriate clinical indication, and the expected benefit outweighs the potential radiation risk. The radiologic technologist supports this process by confirming the correct patient and examination, reviewing the clinical indication and any available prior imaging, and raising questions, as needed, through the appropriate clinical workflow.