Radiation safety in ct
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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.

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Radiation safety in CT

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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

HEMATOPOIETIC

GI

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


HEAD------------ 2

CHEST ---------- 8

ABDOMEN --10-20

PELVIS -------10- 20

SKULL -------- 0.07

CHEST PA ---- 0.02

ABDOMEN --- 1

PELVIS -------- 0.7

EFFECTIVE DOSE (mSv)

CT

CONVENTIONAL


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

DOSE REDUCTION IN CT


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