Shielding Calculation:Radiographic Room

Jerry Williams

h d kWhat you need to know

• Room use and layout– DAP workload– DAP averaged kV– DAP averaged kV– Distance to barrier

• Construction details– Walls– Ceilings/ floors

• Surrounding areas• Surrounding areas– Rooms above or below– Occupancy

kl dDAP Workload

Two approaches:1. Predict clinical usage and use typical 1. Predict clinical usage and use typical

DAP values per exam2. Assume typical total DAP valuesyp

Method 1: DAP data• UK Dose Surveysy

– HPA-RPD-029 – http://www.hpa.org.uk/radiation/

Room doses for 50 90 kg patient sub set – Room doses for 50 – 90 kg patient sub-set – Mean– Min/ max– 25th/ 50th/ 75th percentile values25 / 50 / 75 percentile values

– kV and mAs values

• National Diagnostic Reference Levels– Based on 3rd quartile values – “Boundary between good and normal practice and

bad and abnormal practice”

Radiography doses (1)No of DAP

Projection No of rooms

DAPGy cm2

Skull PA/AP 20 0.78Skull Lat 19 0.49Chest PA 210 0.11Chest AP 12 0.12Chest Lat 23 0.31Thoracic spine AP 36 0.93Thoracic spine Lat 27 1.43Abdomen AP 127 2.58Lumbar spine AP 118 1 60Lumbar spine AP 118 1.60Lumbar spine Lat 120 2.44LSJ 25 2.59Pelvis AP 150 2.12

Source: HPA-RPD Report 029 (2007)

IVU 35 13.60

Radiography doses (2)DAP

Anatomical regionDAP

Gy cm2

Cervical Spine 0.05F 0 04Femur 0.04Knee 0.04Lower leg 0.02Foot/ Ankle 0.02Toes 0.005Shoulder 0.05Elbow/ forearm/ upper arm 0.02Hand/ wrist 0.01Finger 0.005

Source: Personal data

Radiographic workload (UK)0% 10% 20% 30% 40%Frequency 0% 10% 20% 30% 40%

Head

Chest

q yDAP

Abdomen

Pelvis

Spine

Upper extremity

Lower extremity

Data from:

UK examination frequencies – in NRPB Report W4 (2002)

DAP data * HPA-RPD Report 029 (2007)

* personal data (extremities)

Radiographic workload (UK)g p ( )

0% 10% 20% 30% 40%Frequency • Abdo/ pelvis/ spineHead

Chest

Abdomen

DAP Abdo/ pelvis/ spine– 23% frequency– 87% DAP

• ChestPelvis

Spine

Upper extremity

• Chest– 35% frequency– 8% DAP

• ExtremitiesLower extremity

• Extremities– 37% frequency– 1.5% DAP

• Conclusion– To predict DAP workload

– estimate number of abdomen/ spine/ pelvis examinations– Ignore extremities– Chest workload only required for primary beam shielding

Method 2:Method 2:DAP workload in typical rooms

• Survey data from 10 CR consoles– Collection period: 9 to 43 weeks– Number/ type of examination– Number of patients

• Assumption – Images processed on console correspond to

specific X ray roomspecific X-ray room– Average DAP values

Workload surveyWorkload survey

500

600

) 700800

300

400

500cm

2 / wee

k)

400500600700

ts/ w

eek

100

200

300

DA

P (G

y c

100200300400

Patie

nt

01 2 3 4 5 6 7 8 9 10

0100

Examinations per patient

1.41.61.82.0

1.01.21.4

1 2 3 4 5 6 7 8 9 10

Workload• DAP per patient

– Ave: 0 75 Gy cm2

Workload600

700800

– Ave: 0.75 Gy cm

– Range: 0.20 – 1.42 Gy cm2

• Typical workload300

400

500

y cm

2 / wee

k)

400500600700

nts/

wee

k

– No of patients: 180

– DAP: 150

• Exceptional workload0

100

200

DA

P (G

y

0100200300

Patie

n• Exceptional workload

– 24/7 room

– No of patients: 800

01 2 3 4 5 6 7 8 9 10

0

Examinations per patient2.0

– DAP: 500• Examinations per patient

– Ave: 1.321.01.21.41.61.8

1 2 3 4 5 6 7 8 9 10– Range: 1.10 – 1.82

1 2 3 4 5 6 7 8 9 10

DAP averaged kVDAP averaged kV

84868890

kV

78808284

P av

erag

ed

70727476

DA

P

1 2 3 4 5 6 7 8 9 10

Weighted average: 78.2 kV

d lConstruction details

• Floors/ ceilings–Concrete thicknessConcrete thickness–Profile

• Wall construction• Wall construction–Stud partition?

Blockwork?–Blockwork?

dAdjacent areas

• Occupancy–New buildings – assume 100%New buildings assume 100%

• Layout

d hRadiographic Room

1.5 m

6.3 m3.5 m

3 m

1 m

6 m6 m

Lead shielding vs DAP workloadg

1

1.2d = 1 m

d = 1.5 m

0.4

0.6

0.8

d sh

ield

ing

mm

0

0.2

0 100 200 300 400 500 600 700

Lead

Occupancy = 100%• Typical room (DAP = 150 Gy cm2)

DAP workload Gy cm2

Typical room (DAP 150 Gy cm )– 0.45 mm (d = 1.5 m)– 0.6 mm (d = 1 m)

• Exceptional room (DAP = 500 Gy cm2)p ( y )– 0.7 mm (d = 1.5 m)– 0.9 mm (d = 1 m)

UK/ NCRP ComparisonUK/ NCRP Comparison

• Example–NCRP ‘busy’ roomNCRP busy room

• 160 patients/week

–Wall at 1.5 m –100% occupancy–NCRP: 2.5 mA min/ patientNCRP: 2.5 mA min/ patient–UK: 0.75 Gy cm2/ patient

dScatter dose @ 1m

NCRP 147Side scatter

UKMax scatter

3.4x10-2 mGy/ patient5.4 mGy/ weekk/ f d

5.0 µGy (Gy cm2)-1

0.6 mGy/ weekBack/ forward scatter

4.8x10-2 mGy / patient7 7 mGy/ week7.7 mGy/ week

Factor 10 difference?Factor 10 difference?

h ld l lShielding calculation

NCRP• Dose constraint = 20 µSv

B < 0 02/5 4 x 1 52

UK• Dose constraint = 6 µSv

B < 0 006/0 6 x 1 52• B < 0.02/5.4 x 1.52

= 0.8%• Shielding @ workload

h d k

• B < 0.006/0.6 x 1.52

= 2.3%• Shielding @ 80 kV

weighted kV= 0.81 mm Pb

= 0.41 mm Pb

ffDifferences

• Scatter model• Field area assumption• Field area assumption• Patient workload data

D t i t• Dose constraints• Transmission data

d lScatter modelScatter fraction (S) @ 85 kV

10

12

2 )-1

UK

NCRP 147

MonteCarlokV UK NCRP

Smax analysis

4

6

8

µG

y (G

y cm

MonteCarlo

50 4.05 4.1070 4.67 4.4185 5 14 4 64

0

2

0 30 60 90 120 150 180Angle

S 85 5.14 4.64100 5.60 4.87125 6.38 5.26

ldField area

• NCRPF = 1000 cm2F 1000 cm

• UKF incorporated into DAPF incorporated into DAP

F cm2Plate size

8" x 10" 20 x 24 cm2 48010" x 12" 24 x 30 cm2 72014" 17" 35 43 2 150514" x 17" 35 x 43 cm2 1505

Patient workload data

NCRP 147

Patient workload data

• NCRP 147– 2.5 mA min/ patient

• UK datamAs per examinationHPA-RPD

– HPA-RPD-029• kV/ mAs

– Dundee (Dave Sutton)

0 10 20 30 40 50 60 70

Skull PA/AP

Chest PA

mAs per examinationHPA RPDDundee

• Downloaded from RIS• 8 rooms

Chest Lat

Thoracic spine AP

Thoracic spine Lat

Abdomen AP

Lumbar spine AP

Lumbar Spine Lat

Pelvis/ hip AP

Patient workload data

• NCRP 147

Patient workload data

• NCRP 147– 2.5 mA min/ patient

• UK data– HPA-RPD-029

• kV/ mAs high dose exams– Dundee (Dave Sutton)

• Downloaded from RIS• 8 rooms

– Combined with CR workload data– 0.27 mA min/ patient

Factor of 10??

Patient workload data

• Examinations per patient

Patient workload data

• Examinations per patient– US: 3.37– UK: 1.32⇒US: UK Ratio = 2.5

• Types of examination?Period of survey ESD (normalised to 1986)• Period of survey– US: early 1990s– UK: early 2000s

ESD (normalised to 1986)

60%

80%

100%

19861996

20%

40%

60% 199620022007

0%Lat Skull PA Chest AP Lumbar

spineLat Lumbar

spineAP Pelvis

Dose constraints

• NCRP –20 µGy (100 µGy Radiology staff)20 µGy (100 µGy Radiology staff)

• UK6 µGy–6 µGy

Transmission factorsTransmission factors

• NCRP• NCRP– Workload weighted transmission factors

• UK • UK – Workload weighted kV

• For this analysis 78 kV• For this analysis 78 kVB NCRP 80 kV

0.05 0.34 0.270.02 0.54 0.430.01 0.74 0.56

0.005 0.96 0.710.002 1.29 0.920.001 1.55 1.08

WARNING!

• UK workload data apply only in UK• UK workload drivers• UK workload drivers

–Legislation• Justification/ Optimisation• Justification/ Optimisation

–Public Healthcare provision

Derive your own workload dataDerive your own workload data

• Standard specification:–1 mm lead for all radiographic rooms1 mm lead for all radiographic rooms