NEW JERSEY CT DOSE PROJECT UPDATE

New Jersey Medical Physicist Meeting

March 9, 2006

Web version with summary of meeting outcomes

November 2004 Meeting Outcomes

• A standardized method for calculating and reporting CT dose should be used.

• ACR’s 2002 CT Accreditation Program’s method and set up procedures for calculating CT dose should be used.

• BRH to develop a form to report CT dose. • CT dose should be calculated and reported

for Adult Head, Adult Abdomen and Pediatric Abdomen.

• Patient scan protocols should be used.

Meeting Outcomes

• NJ should apply ACR’s CTDI(w) reference values as its reference levels for CTDI(vol).– This will account for pitch from helical scanning

• Facilities will be encouraged to submit CT doses to the BRH.

• BRH will collect and analyze CT dose data and report results to medical physicists.

Why is Monitoring CT Dose Important?

• Some data suggest that CT procedures account for 16% of all radiologic procedures performed, but contribute 65% of the dose delivered to patients.

Analysis of CT Dose Data

• Demographic Information:

– Data includes CT doses collected from December 2004 to February 2006.

– A total of 396 CT Doses were collected on 141 CT scanners. (About 40% of all registered CT scanners)

Percentage of Scanners in Study

1 Slice34%

2 Slice12%

4 Slice19%

8 Slice4%

16 Slice27%

64 Slice4%

CTDI Doses (mGy) By Procedure Type

Procedure/

Parameter

Adult

Head

Adult Abdomen

Pediatric

Abdomen

Number 141 134 121

CTDI(w) Mean 47.67 19.15 16.56

CTDI(w) 80th %tile 59.50 25.46 21.12

CTDI(vol) Mean 49.12 19.33 15.33

CTDI(vol) 80th %tile 60.40 26.00 21.20

AAPM May 2005 recommendation to use 80th percentile

Analysis of Adult Head Dose and Handout #1

Adult Head Mean CTDI Doses

45.97

47.17

52.18

49.3

50.59

52.78

44.26

53.18

50.19

53.75

52.05

52.34

05

1015202530354045505560

1 Slice 2 Slice 4 Slice 8 Slice 16 Slice 64 Slice

CT TYPE

CT

DO

SE

(mG

y)

CTDI(w) CTDI(vol)

Analysis of Adult Abdomen Dose and Handout #2

Adult Abdomen Mean CTDI Doses

20.9

3

19.7

1

19.8

7

19.8

8

16.3

8

13.0

9

19.3

4

19.0

19.8

17.1

15.2

7

10.1

3

0

5

10

15

20

25

30

35

1 Slice 2 Slice 4 Slice 8 Slice 16 Slice 64 Slice

CT TYPE

CT D

OS

E (m

Gy)

CTDI(w) CTDI(vol)

Analysis of Pediatric Abdomen Dose and Handout #3

Pediatric Abdomen Mean CTDI Doses

23.4

12.06

10.04

12.65

12.5

18.07

21.0

10.65

10.12

9.85

10.05

13.5

0.0

5.0

10.0

15.0

20.0

25.0

1 Slice 2 Slice 4 Slice 8 Slice 16 Slice 64 Slice

CT TYPE

CT

DO

SE

(mG

y)

CTDI(w) CTDI(vol)

Percent of CT Doses Above Reference Levels

6

12

22

8

11

18

0

5

10

15

20

25

Adult Head Adult Abdomen Pediatric Abdomen

% A

bov

e R

efer

ence

CTDI(w) CTDI(vol)

Observations and Discussion

• Highest percentage to exceed the Reference Value is Adult Head. – Why? Is ACR’s reference value set too low or are

values for adult abdomen and pediatric abdomen set too high? ALARA? Both?

• High percentage of Pediatric Abdomen CT doses exceed Reference Value and greater variation of doses among CT types. – Suggests a need for better evaluation of patient scan

protocols. (N.J.A.C. 7:28-22.10(a) Item #12)

Adult Abdomen and Pediatric Abdomen Data and Handout #4

Pediatric Scan Protocol

• Is ALARA practiced?

– Scan Protocols between adult abdomen and pediatric abdomen vary greatly depending on CT Slice type.

– CTDI(w) for single slice and 64 slice CT scanners for pediatric abdomen are higher than for adult abdomen.

– No significant change in the mean scan protocol between adult abdomen and pediatric abdomen for 64 Slice CT Scanners.

• CAN DOSE BE LOWER?

New Jersey’s 64 Slice CT Data

60

.4

36

.44

18

.84

0

10

20

30

40

50

60

70

Adult Head PediatricAbdomen

AdultAbdomen

CT

DI(

w)

(mG

y)

GE Siemens 1 Siemens 2 Siemens 3

Revised New Jersey CT Dose Report Form Handout #5

Revisions to New Jersey CT Dose Report

• The following were added to the report:– Field for facility name.– Field to enter procedures not performed.– Auto calculation field for pitch.– Area to enter recommendations for dose and patient

protocol.– Requirement for facilities to implement corrective

action if recommendations are made. – Pediatric patient is defined.

• Physicists are encourages to use this form since it provides data that is not currently on ACR’s form (Examples: CT slice type, review pitch and requirement to reduce high doses).

What’s Next

• Implement revised NJ CT Dose Report form.• Continue tracking CT doses.• Investigate facilities that have a CTDI(vol)

dose that exceed ACR’s CTDI(w) Reference Value.

• Continue to update medical physicists on findings and issues involving CT.

• Physicists to notify the Bureau of issues relating to CT.

Baseline CTDI(vol) Doses (mGy)Data is Established

Procedure/

CTDI(vol)

Adult

Head

Adult Abdomen

Pediatric

Abdomen

Mean 49.12 19.33 15.33

80th percentile 60.40 26.00 21.20

What a Difference 15 Months Makes?

The only available dose data that could be reported in November 2004:

Procedure Type

NJ Range (mGy)

Adult Head 8.3 – 113.0

Adult Abdomen 1.4 – 44.7

Pediatric Abdomen 0.7 -56.8

Doses calculated and reported by various methods (ex. MSAD and Various CTDI)

Establishment of Project Goals

To reduce CTDI(vol) dose in all three procedures by 15% by 2008.

How Can This Be Accomplished?

• Ensure the practice of ALARA by:

– Reviewing patient scan protocol to ensure the lowest CTDI(W) dose possible is used and if possible a greater use of pitch so that CTDI(vol) is lower than CTDI(w) while maintaining acceptable image quality.

– Establishing a committee of physicists and radiologists to examine dose and imaging quality and identify a “suggested” scan protocol that would result in the lowest patient dose while maintain acceptable image quality. Bureau to publish this protocol to facilities.

Major 2006 Meeting Outcomes

• For all three procedures, New Jersey’s mean CTDI(vol) doses are below ACR’s CTDI(w) reference values.

• Facilities experiencing difficulties staying below ACR’s reference value for Adult Head.

• New Jersey’s CT Dose Report is updated to provide better statistical analysis.

• Committee established to optimize dose and image quality for certain CT scanners.