DOSE IN CT by dffhrtcv3

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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!
      HOWEVER:

RADIATION DOSES FROM
 CT SCANNERS ARE THE
HIGHEST IN DIAGNOSTIC
     RADIOLOGY!!!!
  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
  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)
           CT                    CONVENTIONAL
•   HEAD------------ 2     •   SKULL -------- 0.07
•   CHEST ---------- 8     •   CHEST PA ---- 0.02
•   ABDOMEN --10-20        •   ABDOMEN --- 1
•   PELVIS -------10- 20   •   PELVIS -------- 0.7
  DOSE REDUCTION IN CT
• BED INDEX       • DOSE

• SPIRAL PITCH    • DOSE



• COLLIMATION     • DOSE
   (PREPATIENT)

• NOISE           • DOSE
   DOSE REDUCTION IN CT
• SID               • DOSE

• OID               • DOSE



• kVp (15 % RULE)   • DOSE

• mAs
                    • DOSE

								
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