Radiology and Radiation Oncology Physics

CT Imaging and Radiation Exposure

• Figure 40-2 shows isoexposure profiles for horizontal and vertical planes of a multislice helical CT imaging system.

Radiation Dose Limits

• The maximum permissible dose (MPD) was specified to be the dose of radiation that would produce no significant radiation effects.
• Today, dose limits (DLs) are specified not only for whole-body exposure but also for partial-body exposure, organ exposure, and exposure of the general population.
• The whole-body DL is 50 mSv/yr (5000 mrem/yr), which takes into account the weighted average to various tissues and organs.

Occupational Radiation Dose Management

• The recommended dose limit for radiologic personnel is 50 mSv/yr (5000 mrem/yr), but experience has shown that considerably lower exposures than this are routine.
• Occupational radiation exposure of radiologic personnel engaged in general x-ray activity normally will not exceed 1 mSv/yr (100 mrem/yr).
• Radiologists usually receive slightly higher exposures than radiologic technologists due to their proximity to the radiation source during fluoroscopy.

Fluoroscopy

• Fluoroscopy and mobile radiography result in the highest occupational exposure of diagnostic x-ray personnel.
• Personnel exposure is related directly to the x-ray beam-on time, but with care, personnel exposures can be kept as low as reasonably achievable (ALARA).
• Remote fluoroscopy results in low personnel exposures because personnel are not in the x-ray examination room with the patient.

Interventional Radiology

• Personnel engaged in interventional radiology procedures often receive higher exposures than those in general radiologic practice due to longer fluoroscopic x-ray beam-on time.
• The frequent absence of a protective curtain on the image-intensifier tower and the use of cineradiography also contribute to higher personnel exposure.
• Extremity exposure during interventional radiology procedures may be significant, and protective gloves can help reduce exposure.

Mammography

• Personnel exposures associated with mammography are low because the low kVp operation results in less scatter radiation from the patient.
• Rarely does a room that is used strictly for mammography require protective lead shielding.

Computed Tomography

• Personnel exposures in computed tomography (CT) facilities are low due to the finely collimated x-ray beam and low secondary radiation levels in the examination room.