MOD 8 - Minimizing Patient Dose, Dose Limits, DRLs

Learning Objectives

Explain how education and training, equipment specifications, and personnel practices can be used to reduce radiation doses to patients.
Recommend protection for radiology patients taking into account the factors affecting dose in radiography and fluoroscopy.
Explain the guidelines for prescribing x-ray examinations.
Identify the guidelines for irradiating pregnant women.
Describe the guidelines for carrying out radiographic, radioscopic, and angiographic procedures.
Define diagnostic reference levels (DRLs).
Describe the importance of DRLs in the clinical environment.
List the recommended DRL values for radiographic procedures performed on adults.

International Commission on Radiation Protection (ICRP) Principles

Justification
- role of the ordering physician and ALARA principle
Optimization
- customizing exposure factors for diagnostic images at the lowest dose
Dose Limit
- DRL values which are calculated as the 75% percentile of overall exam exposures

Diagnostic reference level (DRL)

= used as a reference value, instead of dose limits

Clinical Evaluation - xray prescriptions MUST be based on clinical evaluation, meaning clinical evaluations are a must for an xray
Screening Programs - radiological screening programs SHOULD not be implemented unless sufficient evidence proves benefit to both individuals and populations
Reviews of Previous Imaging - recommended and SHOULD be reviewed
Imaging to Accompany Patient Transfers - pt transfer to another hospital/physician SHOULD include prior imaging and reports
Detailed History - Radiological requests SHOULD provide detailed history and clinical indications for justification
Minimize Projections/Acquisitions - Imaging exams MUST minimize the number of projections/acquisitions required to satisfy the clinical objective
Ascertain Pregnancy - Pregnancy MUST be ruled out prior to imaging the abdomen and pelvis regions of female patients between 11-55 years of age (pregnancy declaration requires further consultation with ordering physician and radiologist)
Avoid Repeat Projections - Repeat images only when required diagnostic information is not present
Special Procedures - SHOULD only be performed by or in close collaboration with qualified radiologists
Clinical Records - Patient records SHOULD include detailed information about the X-ray exams performed

once declared dose should not exceed 4mSv during the period of pregnancy

Essential Investigations - delay exams if they are not immediately essential to the care of the pregnant patient until after delivery or later in the the term, or consider alternate imaging modalities (ultrasound)
Minimize Exposures - Keep exposures to the absolute minimum, especially around the pelvic regions
- lead shielding is not routinely provided, HOWEVER, if requested it may be used when clinical objectives will not be compromised
Utilize Prone Position - prone position is recommended as there will be reduced exposure to the fetus compared to an AP
Collimate - MUST have demure collimation and proper regard for fetal shielding

lowest possible patient exposure (Automatic Exposure Devices)
Medical Order - all exams must be medically justified (prescribed by a physician)
Shielding - not routinely used, but when requested it can be used if it doesn’t compromise clinical goals, use of shielding MUST be documented
Distance - maximum Source to Skin Distance (SSD)
Optimization - modify technical factors to optimize exposure and minimize dose (especially in pediatrics)
- Use the highest kVp that produces good image quality
- Use anti-scatter grids when appropriate
- Avoid repeat images
- Appropriate collimation
Document
- number of rejected/repeated images for Quality Assurance purposes
- repeat/reject program

Mobile Xray is ONLY done when

pt is unable to transfer to xray room
primary beam is directed away from occupied areas
every effort is made to avoid irradiating surrounding people
operator MUST not stand in the path of the CR
equipment MUST be disabled when left unattended
operator MUST stand at least 3m away from source if not wearing protective apparel

Technologist Mobile Radiation Safety

Patient Radiation Safety

lead shielding can be used upon request
restricted collimation and demonstrating 4-sided collimation
shield surrounding patients or visitors from scatter radiation using lead shielding

Personnel Radiation Safety

New Pregnancy Screening Protocol for Lower Mainland Clinical Sites Only

techs are only required to ask about pregnancy to females between age 11-55 when performing imaging on patients between the diaphragm and the pubic symphysis

This new protocol was implemented due to research findings stating

fetal risks for most extremity and chest exams were measured as negligible
THEREFORE,
- unnecessary to ask about pregnancy for exams outside the pelvis/hip region
- fetal and gonadal shielding should not be used by default

at cruising altitudes for 10 hours equals about 0.03–0.08 mSv
- eg: New York–Paris round trip flight would expose a person to about 0.05 mSv = routine chest X-ray exam

Lead Shielding

why aren’t you giving me LS - can get in the way, cover sensors, and increase radiation dose
aren’t I safer with LS - no evidence to suggest diagnostic imaging exposure is harmful but use of LS can increase patient exposure

Negative Effects of Lead Shielding

increasing internal scatter (scatter travelling out of the body might bounce back into the body due to lead)
causing equipment malfunction if placed too near to the imaging field
exposure to infectious microbes

what to mention

Maximize distance between the X ray tube and the patient
Minimize distance between the patient and the IR
Minimize fluoroscopy time
- Keep records of fluoroscopy time and DAP/KAP
Use pulsed fluoroscopy with the lowest frame rate possible
Avoid exposing the same area of the skin in different projections
- Vary the beam entrance port by rotating the tube
Larger patients or thicker body parts trigger an increase in entrance surface dose (ESD)
Oblique projections also increase ESD
Avoid the use of magnification
Minimize number of frames and cine runs to clinically acceptable level
Use collimation

generated by collecting exposure information for specific procedures and taking the 75th percentile of the distribution median
DRLs are NOT ideal or optimized exposure values, nor dose limits
DRL represents an accepted upper limit of the average exposure values
National DRLs provide general exposure information for the country, but each region should establish their own local DRLs that are BELOW the NDRL
DRLs should be revised every 3-5 years (improved technology, protocols or image processing is adopted)