Radiation Oncology Physics Quiz

Radiation Oncology Physics

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

C-Arm Fluoroscopy

• During C-arm fluoroscopy, the x-ray beam may be on for a relatively long time and can be pointed in virtually any direction.

Radiation Dose Limits

• Radiation personnel should never exceed 50 mSv/yr (5000 mrem/yr).
• In smaller hospitals, emergency centers, and private clinics, occupational exposures rarely exceed 5 mSv/yr (500 mrem/yr).
• Average exposures in most facilities are less than 1 mSv/yr (100 mrem/yr).

Whole-Body Dose Limits

• Today, dose limits (DLs) are specified for whole-body exposure, partial-body exposure, organ exposure, and exposure of the general population, excluding medical exposure as a patient and exposure from natural sources.
• The whole-body DL is 50 mSv/yr (5000 mrem/yr), which is an effective dose that takes into account the weighted average to various tissues and organs.

Dose Limits for Tissues and Organs

• Specific tissues and organs have specific recommended dose limits.
• The DL for the skin is 500 mSv/yr (50 rem/yr).

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).

Fluoroscopy

• Unquestionably, the highest occupational exposure of diagnostic x-ray personnel occurs during fluoroscopy and mobile radiography.
• Personnel exposure is related directly to the x-ray beam-on time.
• With care, personnel exposures can be kept as low as reasonably achievable (ALARA).

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.

Mammography

• Personnel exposures associated with mammography are low because the low kVp of the 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.
• Because the CT x-ray beam is finely collimated and only secondary radiation is present in the examination room, radiation levels are low compared with those experienced in fluoroscopy.