Transcript DOSE IN CT
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 • ABSORBED DOSE ----------- RADIATION • ABSORBED DOSE (rad) • DOSE EQUIVALENT --------- RADIATION EQUIVALENT MAN (rem) (R) 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 • • • • HEAD------------ 2 CHEST ---------- 8 ABDOMEN --10-20 PELVIS -------10- 20 CONVENTIONAL • • • • SKULL -------- 0.07 CHEST PA ---- 0.02 ABDOMEN --- 1 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