PATIENT RADIATION DOSE MANAGEMENT

PATIENT DOSE DESCRIPTIONS

• Exposure of patients to medical x-rays is commanding attention in our society for two reasons

1- Frequency of x-ray examination is increasing in all age groups , about 18% per year , indicates that clinicians are more relying on it for patient care

2- Concern among health officials is increasing regarding risk associated with x-ray exposure.

Increased frequency of acute effects are reported in superficial tissues.

Managing of patient radiation dose involves both the equipment design, which determines the amount of radiation required per image, and the control of the image device by the

operator, who determines the total number of images created during the procedure.

Strauss K J , Kaste S C Radiology 2006;240:621-622

©2006 by Radiological Society of North America

ESTIMATION OF PATIENT DOSE

• Usually reported in one of 3 ways

1- Entrance skin exposure

2- Gonadal dose

3- Dose to bone marrow

ENTRANCE SKIN EXPOSURE

• Also referred to as patient dose• Widely used due to accuracy and easy to

measure

• Thermoluminiscence dosimeters ( TLDs )are used

• Measurements are accurate to within 5%• ESE in fluoroscopy is difficult to estimate because

x-ray field moves

BONE MARROW DOSE

• Also called mean marrow dose• It is average radiation dose to entire active bone

marrow e-g if 50% of active bone marrow receives 25 mrad , then active mean marrow dose is 25 mrad

• Depends on active sites of bone marrow

GONADAL DOSE OR GENETICALLY SIGNIFICANT DOSE

• Important because of genetic effects of radiation• GSD is the dose that if received by every member

of population would produce total genetic effect on population as sum of individual doses actually received

PATIENT DOSE IN SPECIAL EXAMINATIONS

Dose in mammography

• Screen film and digital mammography are the only acceptable techniques

• An ESE of approximately 800 mrad/view is normal• Radiologic grids are used in most screen film

mammographic examinations

• Grid ratio of 4:1 to 5:1 are most popular• Patient dose is increased by 2 times with use of

such grids compared to non grid technique• Fortunately, it is known that risk of adverse

biologic response from mammography is small• Glandular dose variations are noted in x-ray beam

quality and quantity

• Glandular dose is approximately 15% of ESE• Patient dose in mammography can be reduced if

the number of views are restricted• The axillary views should not be done routinely• For screening, no more than 2 views are

advisable

DOSE IN CT IMAGING

• Important consideration in CT imaging is not only the skin dose but also its distribution to internal organs and tissues

• Skin dose is lighter in CT than other diagnostic x-ray procedures

• Data suggest that 10% of all x-ray examinations are CT

• It accounts for 70% of total patient effective dose• CT tissue dose is approximately equal to average

flouroscopic dose• CT dose is nearly uniform throughout the imaging

volume for head examinations• Radiographic/flouroscopic doses are high at

entrance surface and low at exit surface

CONT…..

• Typical CT doses ranges from 3000 --- 5000 mrad during head imaging

• And 2000----4000 mrad during body imaging• Multi slice spiral CT is used which is a high dose

procedure• Higher the multi slice value , lower the patient

dose will be

REDUCTION OF UN NECESSARY DOSE

• Defined as any radiation dose that is not required for patients well being or for proper management and care

UN NECESSARY EXAMINATIONS

• Radiologic technologists has no control over largest source of un necessary patient dose

• Its exclusively the radiologist or clinicians responsibility

• Routine x-ray examinations should not be performed when not indicated

SCREENING FOR TUBERCULOSIS

• General screening for TB by chest x-ray has not been found effective

• Better methods are now available• May be helpful in high risk groups

HOSPITAL ADMISSION

• Chest x-rays should not be done in routine for hospital admission when not indicated

• X-rays are not justified in pre employment physical examinations

REPEAT EXAMINATIONS

• One area of un necessary radiation is repeat examinations

• It is estimated 10% of all examinations• It should not exceed than 5% in busy hospitals• Examinations with high repeat rates are lumbar

spine, thoracic spine and abdomen• Some repeats are caused by equipment failure

• Most repeats are caused by radiologic technologist error

• Also include improper positioning, poor radiographic technique, improper collimation , dirty screens, improper loaded cassettes, high leaks and chemical fog

RADIOGRAPHIC TECHNIQUE

• Use of high kVp technique results in reduce patient dose

• Radiologists must be final judge of radiographic quality

• Slight increase in kVp results in low contrast images

• Proper collimation is essential for good radiographic technique

• With use of collimation, not only effective dose is reduced but image quality is improved with enhanced contrast resolution

IMAGE RECEPTOR

• Image receptor should first be selected for the type of examination

• And 2nd for radiation dose necessary to produce a good quality image

• Rare earth and other fast screens should be used• Such screens are used in orthopedic and chest

PATIENT POSITIONING

• During upper extremities or breast examination, especially when patient is in seated position, care should be taken so that beam does not intercept the gonads

• Position the patient lateral to the beam and provide protective apron as shield

SPECIFIC AREA SHIELDING

• In partial exposure, x-ray examination is controlled by proper collimation and specific area shielding

• Two types of shields are used1- Contact shield2- Shadow shield

• Lens shield and breast shield are of contact type• Gonad shields are of both types

PREGNANT PATIENT

• The most sensitive period to radiation exposure occurs before birth

• Fetus is more sensitive to radiation in early pregnancy than late pregnancy

• It is both time related and dose related

TIME RELATED

• The most critical is first 2 weeks because of ignorance although this time is least hazardous

• Irradiation in first 2weeks results in embryo resorption

• Period from 2 to 10 weeks results in congenital abnormalities

• Most likely congenital abnormalities in later period are neurologic deficiencies

DOSE RELATED

• Although no definite data in humans is available, but in animals there are certain studies

• In utero radiation dose of 200 rad result in these effects

• Reasonable risk suggest that 0.1% of all conceptions would be resorbed after a dose of 10 rad

• 1% increase in congenital abnormalities is estimated to follow a 10 rad fetal dose

• During first trimester, the relative risk of child hood malignancy with radiation is 5----10 and drops 1----4 in third trimester

PATIENT INFORMATION

• Early in pregnancy it is difficult because patient is usually ignorant of her pregnancy

• After 2 months , risk is reduced because patient is aware of her pregnancy

• During pregnancy, x-rays should be avoided unless required

• When required, should be done with care e-g with proper collimation and protective shields

• The protocols vary from complex ( Elective booking ) to simple ( Posting )

• In elective booking, patients last menstrual cycle is determined by radiologist and if early, pelvic shielding would be done

• This can be assessed by patients history

• In posting, if complex method fails, than there should be posted signs in x-ray room or waiting room like “ Are you pregnant?” or “ Could you be?”or warnings about pregnancy.

Thank you