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