Management of Patient Radiation Dose

Limiting Patient Exposure

use proper immobilization and motion reduction techniques, appropriate beam limiting devices, adequate filtration, use gonadal or specific shielding, select suitable technical exposure factors, appropriate digital image processing, avoid repeat exposures

Effective Communication

clear concise instructions, explain procedure in simple terms, allow patient to ask questions, listen attentively answer questions truthfully, create sense of trust between patient and radiographer

Voluntary Motion

controlled through effective communication

Involuntary Motion

controlled through reduced exposure time or immobilization devices as lest resort (piggo-stat)

Gonad Shielding

correctly placed directly over patient’s reproductive organs to provide protection (within 5cm of collimated beam)

Male Supine Shielding

use pubic symphysis to guide shield placement over testes; below pubic symphysis; reduce exposure 90-95%

Female Supine Shielding

shield placed 1in medial to ASIS to protect ovaries; reduce exposure 50%

Flat Contact Shield

used in recumbent AP/PA exams, UNDER patients with fluoroscopic exams

Shadow Shield

suspended from tube, often used in sterile fields

Shaped Contact Shields

radiopaque material contoured to shape of male reproductive organs, good for AP/OBL/LAT fluoroscopic exams; NOT for PA

Clear Contact Shield

plastic impregnated with lead

Protection During Scoliosis

use breast shield if AP because breast tissue radiosensitive(especially teenagers)

Compensating Filters

primarily equals out uneven densities on image caused by abrupt changes in part thickness; secondarily decreases radiation dose

Wedge Filter

used with foot; thick part of filter over thin part of foot to prevent toe burnout

Trough Filter

used with chest x-rays; constructed thin in center and thick laterally; prevents overexposing lungs while maintaining adequate exposure to mediastinum

Beam Limiting Devices

aperture diaphragms, cones, cylinders, collimators

Collimators

most effective and versatile; contains two sets of adjustable shutters(first set reduces off focus radiation and second set reduces scatter and confines beam); also contains light source and mirror

Light Localization Apparatus

illuminates x-ray field, within ±2% of SID

Positive Beam Limitation (PBL)

automatic collimation; works through sensors in bucky tray that relay IR size to collimators, within ±2% of SID

AEC Reducing Patient Exposure

used to terminate exposure for consistent exposure to IR, minimizes repeat exposures, either photomultiplier tube or parallel ionization chamber, requires precise positioning skills, contains back up timer just incase it fails

Filtration

reduces exposure to patient’s skin by hardening the beam

Inherent Filtration

glass envelope, insulating oil, glass window

Added Filtration

collimators, mirrors, aluminum or copper filters

Total Filtration

inherent + added filtration

NCRP Total Filtration

50-70 kVp(1.5mm Al eq); above 70 kVp(2.5mm Al eq)

Technical Exposure Factors

mass per unit volume of tissue of area of clinical interest, effective atomic numbers and electron densities of tissues involved, screen film combo or other type of IR, SID, type and quantity of filtration employed, type of x-ray generator used(single/three/high frequency), balance of radiographic density or brightness and contrast required

Technical Factors

use highest practical kVp and lowest mAs, use efficient crystals in IR(rare earth-gadolinium/lanthanum/yttrium and Csl crystals), grids increase contrast

Grids

increase contrast and patient exposure, moving grids require more exposure than stationary, air gap technique when possible to repalce grid(lateral c spine)

Digital Radiography

use of computer and cassette-based or electronic detector to make radiographic images; computed/direct/indirect

Fluoroscopic Procedures

shows dynamics of anatomic structure; produce greatest radiation exposure in diagnostic field(BE/GI very high)

Fluoroscopy Attire

lead gloves and apron

Fluoroscopy Cord Length

6 feet

Mobile X-Ray SSD

12in (30cm)

Fixed Fluoroscopy SSD

15in (38cm)

Table Top Intensity Routine Fluoroscopy

10 r/min or 100 mGy/min

Table Top Intensity for HLC

20 r/min or 200 mGy/min

Fluoroscopic Analog mA Limit

cannot exceed 5 mA

Fluoroscopy Total Filtration

2.5 mm of Al

Fluoroscopy Protective Side Curtain and Bucky Slot Cover

.25 mm Pb

Fluoroscopy Cumulative Time

5 minutes

Image Intensifier Lead

2 mm lead eq

Minimize Radiation in Fluoroscopy

use pulsed/intermittent fluoroscopy, maximize SID, use last image hold, limit field size(collimate), use high kVp and low mA, position input phosphor of image intensifier as close to patient as possible, use smaller viewing mode(magnification) sparingly, minimize fluoroscopic time, c-arm procedures place tube under patient to reduce scatter and place protective barriers under patient

Fluoroscopically Guided Positioning (FGP)

practice of using fluoroscopy to determine the exact location of central ray before taking radiographic exposure; ASRT and AART does not condone it

Cinefluorography

highest patient dose of all radiographic procedures; used primarily in heart catherization; frame rates of 15/30/60 fps, dose rate increases as frame rate increases, 40 R/min at 30 fps

Digital Fluoroscopy

use pulsed progressive systems to reduce exposure to patient

Amount of Radiation Received by Patient

entrance skin exposure(ESE), skin dose, genetically significant dose(GSD), bone marrow dose, dose area product(DAP)

Genetically Significant Dose (GSD)

equivalent dose to reproductive organs that if received by every human being of child bearing age would be expected to cause an identical gross genetic injury to total population as sum of the actual doses received by individuals in exposed population; .2Sv(20mrem)

Dose Area Product (DAP)

method used to estimate patient radiation dose by incorporating dose and volume of tissue irradiated; measured by detector near collimator cGy/cm²(entrance dose x field area); only used in digital

DAP Dependents

field size(DAP increases with larger field sizes) and not effected by detector distance from source

Fluoroscopic Dose Quantities

kerma; dose measured at center of beam where beam would enter the patient during QC checks; measured in KAP in newer digital in cGy; total dose accumulated during a procedure

KERMA

kinetic energy released in air or energy imparted directly to electrons(compton/photoelectrons) per unit mass

Fluoroscopes After 2006

contain Kar(kerma) and Kar rate(mGy/min)

Fluoroscopy Air Kerma

cannot exceed 10cGy/min(100mGy/min) unless HLC

Mammography

used to detect breast cancer that is not palpable in physical examinations

Mammography Dose Limit

mean dose to glandular tissue of 4.5cm compressed breast mammography system per FDA should not exceed 3mGy per view

Mammography Screening

ACR, ACS, AMA advocate annual screening at least every other year for women ages 40 to 49; before onset of menopause baseline mammogram recommended for comparison with later scans

Mammography Dose Reduction

limit number of projections taken, axillary projections only by radiologist request, perform only craniocaudal and mediolateral projections of each breast with adequate compression to demonstrate breast tissue uniformly from nipple to most posterior portion

Dose Distribution in SIngle Slice CT

1, 2, 2.5, 3 cGy; twice these values for multiple contiguous slices

Helical(Spiral) CT Scanning

x-ray tube emits tightly collimated beam; patient couch moves continuously; scan pitch increase and decrease patient dose

Scan Pitch

couch movement to collimator dimension ratio; I/Z(I is table increment and z is collimator dimension)

Tube mA CT

increasing mA to improve SNR increases radiation dose to patient

kVp CT

higher kVp results in higher dose to patient

Slice Thickness CT

using thinner slices increases patient dose

Smaller Pixel Sizes CT

using smaller sizes for improved resolution without sacrificing SNR increases patient dose

Tube Current Modulation CT

changing modulation of tube current along z axis of patient during scanning

Iterative Reconstruction CT

allows less dose to be used for images that also have decreased noise

Image Gently Campaign

delivers message that CT saves children’s lives but patient dose should be lowered using child size kV/mA, scanning only indicated area, removing multiphase scans from pediatric protocol

Pregnancy Possibility

check pregnancy status between ages 12 and 52

Pregnant Patients Protocol

inquire about LMP; abdominal exams scheduled 10 days after onset of menstruation(ACR deemed obsolete but NCRP 102 supports this on elective abdominal exams); provide gonadal shielding if possible; document pregnancy on appropriate form

NCRP Negligible Risk Level to Fetus

.05 Gy and most medical procedures result in less than .01 Gy absorbed dose

Pregnant Patient Steps

determine possibility of pregnancy, ask date of last menstrual period(LMP), physician makes determination whether or not to do the x-ray; shield recommended if ovaries and uterus less than 5cm from any edge of field

Inadvertent Irradiation of Pregnancy

radiologic physicist should perform calculations necessary to determine fetal exposure; most less than .01Gy risk of abnormality small

Irradiation During Pregnancy Particulars List

x-ray units used, projections taken(including number of images), each projections technical exposure factors(kVp/mAs/image receptor size), SID for each projection, pts AP or lateral dimensions at site of projection, fluoroscopy approximate kVp/mA/duration, spot films include number taken/kVp/mA/exposure time

Pediatric Consideration

decrease dose, use high kVp and low mAs, extra tight collimation, use gonadal shielding, use high mA to decrease exposure time when dealing with motion, use restraints when necessary, use PA on young female scoliosis, avoid use of grids on chest x-rays when tissue thickness less than 10cm