W1 RADIATION FROM CT.pdf

RADIATION PROTECTION INVOLVED CT TECHNOLOGY W1 S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 1  Radiation Protection involved CT techn...

RADIATION PROTECTION INVOLVED CT TECHNOLOGY W1 S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 1  Radiation Protection involved CT technology W1 ILO’s On completion of this section, the student should be able to know the following: Dose Estimation Risk & benefits in various activity Exposure Dose Absorbed Dose Equivalent Dose Effective Dose Dose Measurement – CTDI S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 2  RADIATION PROTECTION INVOLVED CT TECHNOLOGY IN USE DOSE ESTIMATION: Most modern CT systems employ a fan shaped beam of X-rays. The dimensions of the radiation beam are large enough to cover the patient. S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 3  RADIATION PROTECTION INVOLVED CT TECHNOLOGY IN USE Dose should be measured and calculated S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 4  What are the benefits vs. exposure risks? 1. Benefits Unlike other imaging methods, CT scanning offers detailed views of many types of tissue including the lungs, bones, soft tissues and blood vessels. CT scanning is painless, noninvasive and accurate. CT examinations are fast and simple. For example, in trauma cases they can reveal internal injuries and bleeding quickly enough to help save lives. Diagnosis made with the assistance of CT can eliminate the need for invasive exploratory surgery and surgical biopsy. CT scanning can identify normal and abnormal structures, making it a useful tool to guide radiotherapy and other minimally invasive procedures. CT has been shown to be a cost-effective imaging tool for a wide range of clinical problems. S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 5  2. RISKS CT does involve exposure to radiation in the form of x-rays, but the benefit of an accurate diagnosis far outweighs the risk. The effective radiation dose from this procedure is about 10 msv, which is about the same as the average person receives from background radiation in three years. S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 6  Radiation dose in CT work CT imaging parameters that affect dose are: Slice thickness. Noise. Resolution detector efficiency. Reconstruction algorithm. Collimation. Filtration. S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 7  QUANTIFICATION OF DOSE 1. Exposure Dose 2. Absorbed Dose 3. Equivalent Dose 4. Effective Dose S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 8  Exposure Dose Any ionizing beam passing through air causes ionization of the gas molecules and formation of an electric charge. This has been traditionally been measured in term of exposure E E = Q/M (its unit is Ckg-1) Q is total electric charge produced and M is mass of air so the unit is coulombs per kilogram. The old exposure unit of 1 roentgen (R) equivalent to 2.58X10-4 C kg-1. S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 9  Absorbed Dose (Gy) It is a measure of the energy absorbed by a volume of material The absorbed dose in joules/kg is the ratio of energy E absorbed by a mass M of tissue E/M the is the gray (Gy) 1 Gy = 1x10-3 Jkg-1 S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 10  Equivalent Dose (SIEVERT) Dose equivalent allows for this by multiplying the absorbed dose (GY) by a radiation weighting factor which depends on the type of radiation. GY x Wr = Sieverts (Sv). H = WR × D S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 11  The effective dose calculation from 2D kilovoltage setup imaging was performed as the AAPM Task Group 75 recommendation. The conversion coefficients were determined according to the exposure parameters and half value layer of the machine. The parameters and total effective doses are shown in table 1. Table 1. Effective doses and acquisition parameters for each protocol of acuity simulator. kV Parameters Effective Dose (mSv) AP 85 Head Lateral 90 AP 99 Chest Lateral 100 AP 110 Pelvis Lateral 110 It is calculated for the whole body. mAs Field size (cm) 9.97 15.3*15.3 19.46 15.3*15.3 10.16 20.03*20.03 21.58 20.03*20.03 11.86 20.03*20.03 20 20.03*20.03 Conversion coefficient 0.01 0.01 0.12 0.05 0.13 0.07 Effective dose (mSv) 0.01 0.02 0.15 0.16 0.22 0.21 Effective dose (E) is given by the following Total effective dose (mSv) 0.03 0.31 0.43 E =fanW The organ and effective doses from the planning H and cone-beam CT are shown in table 2 T x CT beam and 3 for each region. The dose calculations were performed based on the departmental routine of the planning CT and manufacturer protocol of the Varian cone-beam CT system. For effective dose where, wT calculation, is the tissue weighting the organ factor factors and tissue weighting for tissue and were used H is the equivalent as recommended dose by ICRP 103. Table 2. Organ and effective doses from Philips Brilliance Big Bore CT. Organ Dose, (HT), (mSv) Effective Dose, (HT.WT), (mSv) Organs WT Head Chest Pelvis Head Chest Pelvis Gonads 0.08 0.000032 0.056 28 0 0.0045 2.3 Bone Marrow 0.12 2.5 9.3 7.4 0.3 1.1 0.88 Colon 0.12 0.0011 0.4 16 0.00013 0.048 1.9 Lung 0.12 0.88 31 0.04 0.11 3.7 0 Stomach 0.12 0.027 9.2 0.84 0.0032 1.1 0.1 Bladder 0.04 0 0.025 31 0 0.001 1.2 Breast 0.12 0.13 24 0.04 0.016 2.8 0 Liver 0.04 0.043 13 0.51 0.0017 0.54 0.02 Esophagus (Thymus) 0.04 0.69 34 0.01 0.028 1.4 0 Thyroid 0.04 29 18 0 1.2 0.71 0 Skin 0.01 3.1 6.8 6.7 0.031 0.068 0.07 Bone Surface 0.01 9.7 17 11 0.097 0.17 0.11 Brain 0.01 19 0.39 0 0.19 0.0039 0 Salivary Glands (Brain) 0.01 19 0.39 0 0.19 0.0039 0 Remainder 0.12 4.1 12 5 0.49 1.4 0.59 Total Effective Dose (mSv) 3.3 13 7.2 S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 12  Methods Of Measuring Of Patient Dose BY USING 1- PANICLE CHAMBER 2- COMPUTED TOMOGRAPHY DOSE INDEX PHANTOM ( CTDI PHANTOM ) S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 13  Dose Measurement - CTDI CTDI (peripheral) CTDI (center)  Dose Measurement - CTDI CT DOSE QUANTITIES CTDI 100 CTDI WEIGHTED CTDI VOL  Dose Measurement - CTDI Computed Tomography Dose Index Is a standardized measure of absorbed dose CTDI 100 Is a measure of dose distribution over a pencil ionization chamber ( 10 cm ) S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 16  Dose Measurement - CTDI CTDI weighted Measures a weighted average of CTDI from peripheral radial and central dosimetry points within a phantom and is defined as CTDI = 1 / 3 CTDI100 W CENTER + 2 / 3 CTDI100 PERIPHERAL CTDI c CTDI p S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 17  Dose Measurement - CTDI CTDI volume Gives a weighted average of CTDI from peripheral radial and central dosimetry points within a phantom corrected for pitch. Defined as CTDI vol =( 1 / pitch). CTDI w S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 18  Dose Measurement - CTDI v the pitch is the ratio of the patient table increment to the total nominal beam width for the CT scan ( table distance travelled in one 360° gantry rotation divided by beam collimation) For example, if the table traveled 5 mm in one rotation and the beam collimation was 5 mm then pitch equals 5 mm / 5 mm = 1.0. S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 19  Dose Measurement - CTDI v DLP (dose length product) is the CTDI(vol) multiplied by the scan length in centimeters and is given in units of mGy cm. v size specific dose estimate (SSDE) is a method of estimating CT radiation dose that takes a patient's size into account. v MSAD (Multiple Scan Average Dose) measures radiation dose receive by patient from series of CT scan, between each scan the patient is moved a bed index distance, each slices delivers the characteristic bell-shaped dose. S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 20  Multiple Scan Average Dose MSAD measures radiation dose receive by patient from series of CT scan, between each scan the patient is moved a bed index distance, each slices delivers the characteristic bell-shaped dose. S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 21 S. Jastaniah, J. Al-Ghamdi , A.Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 1/29/24 22