radiation safety in ct. radiation doses during ct exams are classified as: low dose radiation as...
TRANSCRIPT
Radiation safety in CT
RADIATION DOSES DURING CT EXAMS ARE CLASSIFIED AS:
• LOW DOSE RADIATION
AS COMPARED TO DOSES GENERATED FROM NUCLEAR EVENTS
BODY RESPONE TO RADIATION:
• SOMATIC EFFECTS
• GENETIC EFFECTS
SOMATIC EFFECT
• MANIFESTED IN THE INDIVIDUAL EXPOSED
ACUTE SOMATIC RADIATION SYNDROME
STAGES:• PRODROMAL- NAUSEA, VOMITING, DIARRHEA
• LATENT PERIOD – NO SYMPTOMS
• MANIFEST – ORGAN DAMAGE, DEATH OR RECOVERY
HEMATOPOIETICGI
CNS
MOST COMMON SOMATIC EFFECTS
• CATARACT FORMATION
• SKIN CANCER
• THYROID CANCER
• BREAST CANCER
• LEUKEMIA
EFFECT ON AN EMBRYO OR FETUS
• MOST PRONOUNCED DURING THE FIRST TRIMESTER!!!!
ALTERNATIVE EXAMS SHOULD BE SCHEDULED IF
PATIENT IS PREGNANT
CT OR MRI ?
FETAL MRI
GENETIC EFFECT
• MANIFESTED IN THE FUTURE GENERATIONS!
RADIATION DOSES FROM CT SCANNERS ARE THE
HIGHEST IN DIAGNOSTIC RADIOLOGY!!!!
HOWEVER:
RADIATION EXPOSURE SHOULD OCCUR :
• AFTER CONSIDERATION BY THE PHYSICIAN
ALARA
RADIOLOGIC UNITS (CUSTOMARY)
• EXPOSURE, INTENSITY ------ ROENTGEN (R)
• ABSORBED DOSE ----------- RADIATION
• ABSORBED DOSE (rad)
• DOSE EQUIVALENT --------- RADIATION EQUIVALENT MAN (rem)
RADIOLOGIC UNITS (SI)
• EXPOSURE, INTENSITY ------ C/kg
• ABSORBED DOSE ----------- GRAY (Gy)
• DOSE EQUIVALENT --------- SIEVERT (Sv)
1 Gy = 100 rad
1 Sv = 100 rem
PENCIL IONIZATION CHAMBER METHOD OF MEASURING CT
DOSE(CT DOSE INDEX---CTDI)
CT PHANTOM & IONIZATION CHAMBER
PRINCIPLE OF OPERATION OF IONIZATION CHAMBER
THE AMOUNT OF COLLECTED CHARGE IN I.C. IS PROPORTIONAL TO THE
AMOUNT OF IONIZATION WHICH IS PROPORTIONAL TO THE AMOUNT OF RADIATION PASSING THROUGH THE
CHAMBER. THE TOTAL ELECTRIC CHARGE GENERATED BY AN X-RAY BEAM IS REPRESENTED BY Q AND IS
MEASURED IN COULOMBS.
IN 1981 CENTER FOR DEVICES AND RADIOLOGICAL HEALTH SUGGESTED AN
EASY AND ACCURATE METHOD TO MEASURE PATIENT DOSE IN CT. IT RELIED ON ON CTDI AND MSAD
(MULTIPLE SCAN AVERAGE DOSE)
MSAD
• SERIES OF CT SCANS ARE PERFORMED ON A PATIENT . BETWEEN EACH SCAN PATIENT IS MOVED A BED INDEX (BI) DISTANCE.
MSAD vs CTDI
FACTORS IN PATIENT PROTECTION
• TIME
• DISTANCE
• SHIELDING
SHIELDING
• IF PERSONNEL PRESENT IN THE ROOM DURING SCAN MUST BE SHIELDED AND STAND FAR FROM THE SOURCE
( INVERSE SQUARE LAW)
GONADAL SHIELDS
• 4-5 CM WITHIN THE X-RAY BEAM
CONTACT SHIELDS
360 ° AROUND PATIENT
CT DOSE IN SPIRAL SCANNING
• CTDI CAN ALSO BE USED
PITCH
MSAD OR CTDI
MORE USEFUL MEASUREMENT IS
• EFFECTIVE DOSE
TAKES INTO ACCOUNT QUALITY OF RADIATION
AND ORGAN SENSITIVITY
EXPRESSED IN Sv
EFFECTIVE DOSE (mSv)
• HEAD------------ 2• CHEST ---------- 8• ABDOMEN --10-20• PELVIS -------10- 20
• SKULL -------- 0.07• CHEST PA ---- 0.02• ABDOMEN --- 1• PELVIS -------- 0.7
CT CONVENTIONAL
DOSE REDUCTION IN CT
• BED INDEX
• SPIRAL PITCH
• COLLIMATION (PREPATIENT)
• NOISE
• DOSE
• DOSE
• DOSE
• DOSE
DOSE REDUCTION IN CT
• SID
• OID
• kVp (15 % RULE)
• mAs
• DOSE
• DOSE
• DOSE
• DOSE