2. 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
3. 2- Concern among health officials is increasing
regarding risk associated with x-ray exposure.
Increased frequency of acute effects are reported
in superficial tissues.
5. ESTIMATION OF PATIENT DOSE
• Usually reported in one of 3 ways
1- Entrance skin exposure
2- Gonadal dose
3- Dose to bone marrow
6. 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
7. 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
8. 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
9. 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
10. • 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
11. • 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
12. 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
13. • 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
14. 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
15.
16. REDUCTION OF UN NECESSARY DOSE
• Defined as any radiation dose that is not required
for patients well being or for proper management
and care
17. 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
18. 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
19. 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
20. 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
21. • 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
22. 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
23. • With use of collimation, not only effective dose is
reduced but image quality is improved with
enhanced contrast resolution
24.
25. 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
26. 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
27. SPECIFIC AREA SHIELDING
• In partial exposure, x-ray examination is controlled
by proper collimation and specific area shielding
• Two types of shields are used
1- Contact shield
2- Shadow shield
28. • Lens shield and breast shield are of contact type
• Gonad shields are of both types
29. 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
30. 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
31. 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
32. • 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
33. 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
34. • 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
35. • 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.
