Regional diagnostic reference levels and collective effective doses from CT scanners in India Roshan S Livingstone and Paul M Dinakaran Department of Radiology Christian Medical College, Vellore, S India
OUTLINE Introduction Survey on CT scanners in South India Dose measurements in CT Regional diagnostic reference Levels (RDRL) Collective doses Awareness Summary
INTRODUCTION Increased and unjustified use of radiation based modalities for diagnosis Increased use of CT scanners Inadequate training and education with the use of these modalities Radiation safety is of concern for both patient and staff
Survey on CT scanners in S. India Evaluate radiation doses and radiation safety concerns Bring about awareness in radiation protection Establish Regional Diagnostic Reference Levels (RDRL) in S. India. Guidance levels Collective doses Atomic energy regulatory board (AERB) funded project
Survey Questionnaire Location of the installation Type, model of the scanner Exposure parameters used routinely Number of scans performed per day Availability of dose reduction techniques and dose derivatives in the console Calibration details of machines
Survey 20 districts in S. India State of Tamil Nadu On-site measurements in 127 CT scanners Conventional - 24 Machines Spiral - 59 Machines Multislice - 44 Machines
Survey Types of Machines Conventional - 13 Machines Con. Refurbished - 11 Machines Spiral - 53 Machines Spiral. Refurbished - 6 Machines Multi detector - 44 Machines Total - 127 Machines Over 2100 patients are subjected to CT scan examinations each day in the region. ~ 3 % are pediatric patients
Survey CT scanner installation details Residential areas 13% Installations in commercial areas 33% Hospital based installations 54%
Dosimetry CT Dose Index (CTDI) measurement - 32cm PMMA body phantom - 10 cc pencil Chamber -Radcheckreader
Dosimetry.. CTDI w = 1/3 CTDI 100,c + 2/3 CTDI 100,p DLP = CTDI vol * Scan length (cm) DLP Dose Length Product Effective dose (msv) = DLP * k k Conversion factor abdomen = 0.015 Thorax = 0.017 Pelvis = 0.019 CTDI 100 = (Dose (mgy) * C * f * L) / (N * T) C - Calibration factor for electrometer F - conversion factor from exposure from dose in air (0.87) L - Length of the chamber N - No of slices acquired T - Thickness of the slice European Commission, 1999
Dosimetry Exposure parameters Dosimetry involved use of Standard exposure parameters Calculation of CTDI values Routine parameters Specific Protocols routinely used Thorax, abdomen, pelvis Calculation of CTDI values Used for regional reference levels
Regional diagnostic reference levels DLP values were used Based on rounded third quartile values Baseline for future National diagnostic reference level.
Regional Diagnostic reference levels for CT examinations CT examination (Mean scan length) Thorax (36.1 cm) Abdomen (33.8 cm) Pelvis (19.1 cm) DLP in mgy cm Mean ± SD Range 476 ± 191.67 (113.72 1465.4) 445.8 ± 179.46 (106.5 1372) 251.9 ± 101.41 (60.17 775.29) Third quartile European Commission 557 650 521 780 294 570
Contribution to collective effective dose In S. India Technological improvements has led to tremendous increase in number of CT scanners >44 MDCT scanners since 2000 Over 2100 scans are performed each day Modality of choice by clinicians
CED = ΣE i N i where E i mean Eff dose; N i - # of cases; 14.93 man.sv /day Districts Vellore Tiruvanamalai Villupuram Pondichery Cuddalore Thanjavur Trichy Madurai Kanyakumari Tirunelveli Tuticorin Virudhunagar Kancheepuram Chengalpattu Salem Coimbatore Erode Karur Namakal Chennai Collective Effective doses No of machines 7 2 1 3 3 5 8 10 4 5 3 2 3 1 8 9 6 1 1 45 No of cases per day (N i ) 166 33 7 23 49 54 100 293 50 63 47 8 29 9 115 194 84 7 7 769 Population in the region (2001 census) 3477317 2186125 2960373 973829 2285395 2216138 2418366 2578201 1676034 2723988 1572273 1751301 2877468 62631 3016346 4271856 2581500 935686 1493462 4343645 Effective dose per exposed individual per day (msv) E i 6.75 8.07 9.88 9.21 7.53 6.49 7.4 9.9 5.7 6.7 15.2 8.1 6.8 7.9 7.9 6.4 6.7 8.3 8.6 5.6 Collective Effective dose per day (man Sv) E i N i 1.12 0.27 0.07 0.21 0.37 0.35 0.74 2.9 0.3 0.42 0.71 0.06 0.2 0.07 0.91 1.25 0.56 0.06 0.06 4.32
Mean effective doses from Thorax CT examinations - Survey 70 60 66 30 machines > range 5 8 msv range from Literature* 50 No of Installations 40 30 20 31 22 10 3 5 0 1 to 5 5 to 8 8 to 10 10 to 12 Above 12 Effective doses in msv *Mettler et al, 2008
Mean effective doses from abdomen CT examinations - Survey 60 50 48 28 machines > range 8 10 msv range from Literature* No of Installations 40 30 20 19 32 18 10 10 0 1 to 5 5 to 8 8 to 10 10 to 12 Above 12 Effective doses in msv *Mettler et al, 2008
Mean effective doses from Pelvis CT examinations - Survey No of Installations 80 70 60 50 40 30 20 76 3 machines > range 8 10 msv range from Literature* 48 10 0 1 to 5 5 to 10 10 and above Effective dose in msv 3 *Mettler et al, 2008
Why there is an increase of doses in a few installations? Types of Machines Conventional Conventional* Spiral Spiral* Dual slicer 4 slicer 6- Slicer 8- Slicer 16-Slicer 24- Slicer 64- Slicer Exposure parameters, CTDI w and Effective doses for thorax CT examinations Mean Tube potential (range) 122 (120-130) 119 (110-130) 121 (110-130) 120 123 (120-130) 120 120 (110-130) 120 120 120 122 (120-135) Mean mas (range) 205 (150-270) 215 (130-360) 188 (70-510) 242 (150-300) 189 (60-510) 183 (120-300) 188 (140-240) 340 400 200 215 (140-300) Mean CTDI vol ±S.D (range) 13.6 ± 2.25 (10.2-16.7) 13.3 ± 3.59 (8-20.45) 12.6 ± 5.14 (5.5-36.5) 15.6 ± 3 (11.8-19.1) 11.97 ± 6.6 (3.15-28.63) 13.4 ± 4.3 (11-22.03) 13.6 ± 4.13 (10.23-20.5) 13.37 40.59 11.8 13.72 ± 3.89 (6.29-18.4) Thorax Effective dose in msv ± S.D (range) Minimum Scan length (26.5 cm) 6.12 ± 1.02 (4.61-7.51) 5.99 ± 1.62 (3.6-9.2) 5.68 ± 2.32 (2.5-16.44) 7.02 ± 1.14 (5.32-8.6) 5.4 ± 2.96 (1.42-12.9) 6.04 ± 1.9 (4.96-9.9) 6.11 ±1.86 (4.6-9.2) 6.02 18.29 5.32 6.18 ± 1.75 (2.84-8.3) Maximum Scan length (40 cm) 9.24 ± 1.53 (6.95-11.3) 9.04 ± 2.44 (5.46-13.9) 8.58 ± 2.32 (2.5-24.82) 10.6 ± 1.72 (8-12.95) 8.14 ± 4.5 (2.14-19.5) 9.11 ± 2.9 (7.5-15) 9.22 ± 2.8 (6.95-13.9) 9.09 27.6 8.02 9.33 ± 2.64 (4.28-12.5) Mean Scan length (36.1 cm) 8.34 ± 1.38 (6.28-10.23) 8.15 ± 2.2 (4.9-12.6) 7.62 ± 3.2 (3.2-22.4) 9.56 ± 1.55 (7.24-11.7) 7.34 ± 4.03 (1.93-17.6) 8.22 ± 2.62 (6.76-13.5) 8.32 ± 2.54 (6.3-12.6) 8.21 24.91 7.24 8.42 ± 2.4 (3.9-11.3)
AWARENESS Lack of qualified staff Unjustified use of CT scans Only 58% scanners had dose descriptives such as CTDI, DLP, CTDI w, CTDI vol or effective doses displayed on the control console Lack of quality assurance programs
Awareness.. Inadequate frequency of machine calibrations Out of 127 scanners surveyed 73 centers have calibrations once in every 6 months to 1 year. 109 machines have routine warming up Purchase of refurbished scanners
SUMMARY Over 2100 CT examinations conduced per day Over 175 CT scanners for a population of 46.4 million Mean effective dose to an individual per day was 7.95 ± 2.1 msv (5.61 15.18) Collective dose in the region was 14.93 man Sv
Summary.. Need for Proper orientation of personnel Education and training Standard protocols for examinations Licensing of personnel Periodic monitoring of doses Establishment of National reference levels Dose reduction strategies Periodic Quality assurance in machines
Summary.. The reported RDRLs were within the guidance levels reported in literature
ACKNOWLEDGEMENT Thanks to AERB of India for funding the project
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References European guidelines on quality criteria for computed tomography - EUR 16262 report Mettler et al. Effective doses in radiology and diagnostic Nuclear Medicine. Radiology 248; 2008. 254-263 http://rpop.iaea.org/