Radiation Doses from the ACR CT Accreditation Program: New Diagnostic Reference Values and Pass/Fail Limits Cynthia McCollough, Ph.D. Michael McNitt-Gray, Ph.D. J. Thomas Payne, Ph.D. Tom Ruckdeschel, M.S. Doug Pfieffer, M.S. Dianna Cody, Ph.D.
Robert Zeeman, M.D. Vince Herlihy, M.D. Theresa Branham, RT(R) (CT) (QM) Krista Bush, RT(R) (M) (CT) MBA Lavonne Robbins B.S., C.N.M.T. Mythreyi Bhargavan, Ph.D.
• Have been shown to lower average dose in other modalities and/or other countries • Represent the upper third or quartile of doses sampled from actual practice data • Do not represent ideal or suggested doses • Identify when dose is unusually high Gray JE, et al . Reference values for diagnostic radiology: application and impact. Radi ology 2005; 235: 354-358. Tsapaki V, et a l. Dose reduction in CT while mainta ining diagnostic confidence: Diagnostic reference levels at routine head, chest, and abdo minal CT--IAEA-coordinated resea rch project. Radiology 2006; 240:828 -834. Hart D, et al. Doses to patients from medical x -ray examinations in the UK —1995 review. In: Chilton: NRPB -R289, 1996. Shrimpton PC, et al. Doses from Computed Tomog raphy (CT) Examination s in the UK - 2003 Review. In: National Radiological Protection Board, Oxon: NRPB -W67, 2005.
Phantom size affects CTDI values
• ACR CT Reference Doses – Adult Head – Adult Abdomen – Pediatric (5 yr old) Abdomen
Reference Doses
Same kVp, kVp, collimation, pitch
60 mGy* 35 mGy* 25 mGy
Body (32 cm)
Head (16 cm)
280 mAs
116 mAs
÷ 2.4 =
20
• Currently no pass/fail dose criteria
16.6
– Justification or corrective action requested • New CTDI data and images • Low contrast resolution images • Statement that clinical image quality is acceptable
20
10
20
*From European Commission EUR 16262 (2000) European Guidelines on Quality Criteria for Computed Tomography
CTDIw = 16.6
20
16.6
16.6
16.6
16.6 CTDIw = 16.6
Materials & Methods • Use of smaller phantom and lower reference value implies that a reduction in tube output by a factor of to 3 - 4 is expected for a 5 y.o. abdomen exam • CTDIvol values displayed on the scanner console use large CTDI phantom – Need to address with appropriate standards, professional and manufacturer organizations, as well as clearly educate users
Site Dose Measurements
Excel® “Dose Calculator” spreadsheet Dose Calculator spreadsheet available for exposure or air kerma meters
• CTDIw (mGy) for – Routine head (cerebrum/brain) – Adult abdomen – Pediatric abdomen (5 y.o)
• CDTI phantom images filmed to verify correct technique
Center Measurement 1 (mR)
197
Measurement 2 (mR)
199
Measurement 3 (mR)
199
Average of above 3 measurements (mR)
2:9 198.3
Body CTDI at isocenter in phantom (mGy)
11.2
12 o'clock position Measurement 1 (mR)
401
Measurement 2 (mR)
422
Measurement 3 (mR)
401
Average of above 3 measurements (mR) Body CTDI at 12 o'clock position in phantom (mGy) CTDIw (mGy)
408.0 23.0 19.0
CTDIw = 2/3 CTDI100 (edge) + 1/3 CTDI100 (center)
Reviewer Validation • Adult Head – 16 cm CTDI phantom, in head holder CTDIw (mGy) 19.0 Clinical exam dose estimates (using measured CTDIw and site's Adult Abdomen Protocol from Table 1) CTDIvol (mGy)
=CTDIw*N*T/I
25.4
DLP (mGy-cm)
=CTDIvol*25
634.2
Eff Dose (mSv)
=DLP*0.015
9.5
• Pediatric abdomen (5 y.o.) – 16 cm CTDI phantom, on table
• Adult Body – 32 cm CTDI phantom, on table
Volume CTDI = CTDIw / pitch
• Axial scan mode • Correct detector configuration • Invalid data omitted from analysis
Data Analysis
Results I
• Average, standard deviation, and histogram determined
Mean ± standard deviation
– By exam (head, abdomen, pediatric abdomen) – By year (2002, 2003, 2004, and 2002-2004) – By CTDIw and CTDIvol
• Statistical significance of changes in average doses by year tested using a 2-tailed t-test • Percent of scanners above references dose determined – Current reference dose using CTDIw and CTDIvol – Proposed reference dose using CTDIvol
Shown for CTDIvol only
Adult Head
90
Adult Abdomen
30
80 25
66.7 59.1
57.8
60
CTDIvol (mGy)
CTDIvol (mGy)
70
54.6
50 40 30 20
P < 0.0001
10
18.4 17.0
15 10 NS
5
P < 0.0001
19.2
18.7
20
NS
P < 0.005
NS
0
0 2002 (n=117)
2003 (n=305)
2004 (n=208)
2002 (n=113)
2002-2004 (n=630)
2003 (n=290)
% > Current Reference (CTDIw)
Pediatric (5 y.o.) Abdomen
30
50
2004 (n=197)
2002-2004 (n=600)
% > Current Reference (CTDIvol)
Head
45
CTDIvol (mGy)
25 20
40 35
17.2
15.9
30
15.5 14.0
15
%
25 20
Pediatric Abdomen
10 15 P < 0.05
5
10
NS
P < 0.01
Abdomen
5
0 2002 (n=91)
2003 (n=224)
2004 (n=151)
2002-2004 (n=466)
0 2002
2003
2004
20022004
2002
2003
2004
20022004
2002
2003
2004
20022004
Conclusions I Results II
• Dose for three high-use exams have decreased significantly in the U.S. since 2002 – Adult head
• Percent above references dose • Establishing new reference doses
– Adult abdomen – Pediatric abdomen
– Maintained 5 mGy “step size”
• Sites are “dialing down” the dose for kids
• Mandatory dose limits
– About a factor of 3
• ACR CT Accreditation program has developed a valuable database to monitor dose trends and to establish new reference doses • ACR will switch to CTDIvol to include the effect of pitch
Pediatric Abdomen
28
Adult Abdomen
32 75%tile
26.6 26
30.6
75%tile
29.5
30
90%tile
25.6
29.5 90%tile
24
CTDIvol (mGy)
CTDIvol (mGy)
24.9 23.4
22 20.6
20.5
28
24
23.4 22.6
20.0 20
25.8
26
22.2
22
21.1
18.4 18
20 2002 (n=91)
2003 (n=224)
2004 (n=151)
2002-2004 (n=466)
2002 (n=113)
2003 (n=290)
2004 (n=197)
2002-2004 (n=600)
Adult Head
Adult Head
2002 Frequency 2002 Cumulative %
2003 Frequency 2003 Cumulative %
2004 Frequency 2004 Cumulative %
30
100% 90%
25
80% 70%
20
60% 15
50% 40%
10
Cumulative %
• 75%tile difficult to determine because initial reference values altered the practice distribution • Numerous sites felt the 60 mGy was not clinically acceptable • Multiple reports of sites increasing head dose after accreditation process completed
30% 20%
5
10% 0
0% 120
CTDIw (mGy)
Adult Head
2002 Frequency 2002 Cumulative %
2003 Frequency 2003 Cumulative %
Adult Head
2004 Frequency 2004 Cumulative %
2002 Frequency 2002 Cumulative %
2003 Frequency 2003 Cumulative %
2004 Frequency 2004 Cumulative %
30
100%
30
100% 90%
90% 25
25
80%
80%
74.60%
15
50% 40% 75
10
30% 20%
5
Cumulative %
60%
70%
20
60% 15
50% 40%
10
30% 20%
5
10%
10% 0
0% 120
0
0% 120
Cumulative %
70%
20
2002 Frequency 2002 Cumulative %
2003 Frequency 2003 Cumulative %
Adult Head
2004 Frequency 2004 Cumulative % 100%
2002 Frequency 2002 Cumulative %
2003 Frequency 2003 Cumulative %
2004 Frequency 2004 Cumulative % 100%
30
90%
90% 25
25
80%
77.57%
70% 60% 50%
15 65
40%
10
70% 60% 50%
15
40% 10
30% 20%
5
80%
20 Cumulative %
20
30% 20%
5
10%
10% 0
0
0% 120
CTDIw (mGy)
CTDIw (mGy)
2003 Frequency 2003 Cumulative %
2004 Frequency 2004 Cumulative %
30%
Multiple Scan Average Dose (comparable to CTDIw for contiguous sca
100%
30
2000-01 (n = 203)
60
25%
90% 25
1990
80% 76.17%
50% 40%
10
30%
Cumulative %
60% 15
(n = 249)
20%
70%
20
15%
28% > 60 15% > 70
10% 5%
20%
0% 120
0%
MSAD (mGy)
Data courtesy of Stanley Stern, Ph.D. - U.S. FDA 2001
>1 00
10% 0
010 10 -2 0 20 -3 0 30 -4 0 40 -5 0 50 -6 0 60 -7 0 70 -8 0 80 -9 0 90 -1 00
5
Cumulative %
Adult Head 30
ACR vs. NEXT data (Head) New UK Diagnostic Reference Levels
• NEXT 1990: 45.9 mGy ± 18.1 (n=249) Solid state detectors become standard, spiral CT and higher power tubes introduced, slice width begins to decrease
• NEXT 2000: 50.3 mGy ± 19.4 (n = 203) MDCT introduced in 1999, SDCT techniques used on MDCT, slice width continues to decrease
Brain Posterior Fossa
SSCT 65 55
MSCT 100 65
• ACR 2002: 66.8 mGy ± 23.2 (n = 127) • ACR 2003: 58.1 mGy ± 17.4 (n = 321) Shrimpton et al. Doses from CT Examinations in the UK – 2003 Review. NRPB-W67 (NRPB, Chilton) 2005.
• ACR 2004: 55.5 mGy ± 15.5 (n = 214)
Adult Head
110 99.0
CTDIvol (mGy)
100
75%tile
• New ACR CT Reference Doses
90%tile
– Adult Head – Adult Abdomen – Pediatric (5 yr old) Abdomen
90 82.2 80
81.3
76.8
70
74.0 64.3
63.9 60.0
60 50 2002 (n=117)
2003 (n=305)
2004 (n=208)
2002-2004 (n=630)
60 → 75 mGy 35 → 25 mGy 25 → 20 mGy
% > Current Reference (CTDIw)
% > Proposed Reference (CTDIvol)
Conclusions II
50
Head 45
• Have sufficient data for new U.S. reference doses
40
• Based on CTDIvol to include the effect of pitch
35
Pediatric Abdomen
30
%
25
Abdomen
20
• Reference doses (site given educational information) – Adult Head
60 → 75 mGy
– Adult Abdomen
35 → 25 mGy
– Pediatric (5 yr old) Abdomen
25 → 20 mGy
• Maximum allowable doses (site fails if these are exceeded)
15 10
– Adult Head
80 mGy
5
– Adult Abdomen
30 mGy
0
– Pediatric (5 yr old) Abdomen
25 mGy
2002
2003
2004
20022004
2002
2003
2004
20022004
2002
2003
2004
20022004
Additional Program Refinements • Simplified Film Page 1 – Elimination of need to convert spiral into axial – CT number of non-water rods only at 120 kVp – Fewer slice thickness scans
• New results database • WIP – – – –
New performance limits Accommodation of non-traditional CTDIvol measurements Quality control manual Electronic submissions
• Effective January 1, 2008
Thank you