The effect of source to image-receptor distance(SID) on

radiation dose for digital chest x-ray examination.

Soon-Mu Kwon1, Ki-Hong Kim2, Kil-Ju Na3, Man-Seok Han4, Do-Guwn Hwang5

1Department of Radiological Technology, Daegu Health College 2Department of Radiologic Technology, Choonhae College of Health Sciences

3Department of Radiological Technology, Mokpo Science University 4Department of Radiological Science, Kangwon National University

5Department of Oriental Biomedical Engineering, Sangji University

CONTENTS

0505

0404

0303

0101 Introduction

Results

Discussion

Conclusion

0202 Materials & Methods

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Introduction

§ Chest X-Ray Examination

(건강보험심사평가원)

2001년 2002년 2003년 2004년 2005년 2006년

합 계 5,910,644 8,147,169 10,273,694 11,201,557 12,025,984 12,883,042

전문종합병원 2,013,672 2,673,843 3,214,940 3,345,518 3,389,440 3,615,537

종합병원 1,030,944 1,817,790 2,884,484 3,351,797 3,767,737 4,102,709

병 원 148,740 455,359 779,255 1,127,935 1,522,944 1,766,488

의 원 2,717,288 3,200,177 3,395,015 3,376,307 3,345,863 3,398,308

증가율(%) - 37.8 26.1 9.0 7.4 7.1

§ UNSCEAR Report 2000

§ Diagnostic Reference Level (DRL)

§ Diagnostic Reference Level for Chest Radiography (KFDA, 2008/2012)

Classification Film-Screen Computed Radiography Digital Radiography

ESD/radiography (mGy) 0.18 0.37 0.32

Tube voltage (kVp) 96 110 120

Exposure current (mAs) 7.2 9.3 5.0

SID (cm) 180 180 180

Grid ratio 8:1-12:1 10:1-12:1 10:1-12:1

DRL for Chest Radiography (ESD/radiograph)

Basic Safety Standards No. 115(WHO, IAEA et, al. 1996)

EU USA* UK JR

0.4mGy 0.3mGy 0.13mGy 0.15mGy 0.3mGy

Introduction

* : ESE/radiography

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Introduction

Diagnostic Reference Level for General Radiography (KFDA, 2012)

§ 촬영조건에 따른 방사선량 및 영상화질에 대한 이해 필요

§ 방사선검사에 의한 의료상 목적은 달성하고 선량은 최저화할 수 있는 촬영 프로토콜의 개발

§ 가능한 전류‧시간곱을 최소로 유지

§ 방사선검사에 필요한 부분만 피폭되도록 최소의 조사야 사용

§ 높은 관전압 사용을 권고

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§ Advantages of chest radiographys

•Rapidity.

•Low cost.

•Low radiation exposure.

§ Chest radiography

•Long-FFD(Almost x-ray examination : FFD 100cm)

•Superior image sharpness suitable for use as clinical photographs.

•Good visualization of cardiac posterior and trachea shadow regions in the diaphragm.

§ ICRP publication 16

•Short FFD : Entrance surface dose > Image receptor dose.

•FFD increases : the ratio between ESD and image receptor dose decreases.

•Patient’s dose-reducing method : Increasing the FFD(SID)

Introduction

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§ Korea Food and Drug Administration, EC Guideline.

• Recommends Source to image-receptor distance (SID) 180 cm.

§ Inadequate setting SID

• Increasing entrance skin dose

• Increasing the risk of deterministic and stochastic radiation effects.

Introduction

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Vinita Merrill (1905-1977)

Introduction

• Reduces patient dose and image quality in a variety of forms for improving the

optimization of the DR.

• Analog (Film / Screen type) have been recommended in the SID is preserved in the

digital radiography.

• In digital chest radiography, Image quality and patient dose were investigated

according to increased SID with the AEC

Whenever possible, a minimum SID of 72 inches(183 cm)

should be used to minimum magnification of the heart and to

obtain greater recorded detail of the delicate lung structures.

1949, 1st edition

2012, 12th edition

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§ Dosimetry

• Basic beam quality (kVp, mAs, Sec, Half Value Layer)

• Entrance surface exposure(ESE) [mGy]

• Entrance surface dose(ESD) [mGy]

• Effective dose (ED) [mSv]

§ Assessment of image quality

• SNR (signal to noise ratio)

• FOM (figure of merit)

• CTR (cardio-thoracic ratio)

& Cardiac diameter

• VGA (visual grading analysis)

1. Experimental design

§Exposure parameter : 120 kVp, 320 mA, AEC.

§SID : 20 cm intervals, 160 cm ∼ 340 cm.

Materials & Methods

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§ Imaging System

• GE Discovery XR 650 (GE Medical System, USA)

• Cesium iodide-amorphous silicon image detector

: 194 μm pixel pitch, 3933 mm × 3925 mm(2017×2013 matrix)

• Focal spot size 0.6 mm

• Inherent filtration 0.8 ㎜Al Eq. (additional filter not used)

• Stationary parallel pattern grid : Grid ratio 12:1

Materials & Methods

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① Basic beam quality(kVp, mAs, Sec, HVL)

② ESE / ESD [mGy]

•Multi function tester (RaySafe Xi, Sweden)

•Chest anthropomorphic phantom (PBU-60, Kyoto Kagaku)

•SPSS (SPSS Inc, Chicago, USA) 22.0

§Backscatter factor (B)

• ICRP 93 : 1.2∼1.4

• CEC : 1.3∼1.4

1. Dosimetry

Materials & MethodsMaterials & Methods

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③ ED [mSv]

•PC- Based Monte Carlo package (PCXMC, STUK, Radiation and Nuclear Safety

Authority, Helsinki, Finland)

•PCXMC calculates the effective dose with both tissue weighting factor of ICRP

publication 103 and 60.

Materials & MethodsMaterials & Methods

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§ ICRP’s 2007 Recommendations on Radiological Protection(Publication 103)

Materials & Methods

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① SNR

•ANSI (American National Standards Institude) sensitometry chest phantom

•Al Plate(20 mm×40 mm×4 mm)

•“Image J” (1.46r / National institutes of health, USA)

•Region of interest (ROI) : 2500 pixels (50 pixel×50 pixel)

2. Assessment of image quality

Materials & Methods

N

S

Materials & Methods

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② FOM

• FOM demonstrate basic relationship between radiation dose and image quality

that can be applied in optimization of radiological system.

③ CTR(%) & Cardiac diameter(mm)

• GE Centricity RA600 workstation (GE healthcare, USA)

• 2-megapixel(1600×1200 pixels) monitor

(MDRC-2120, Barco, Belgium)

2. Assessment of image quality

Materials & MethodsMaterials & Methods

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④ Visual grading analysis (VGA)

•Chest anthropomorphic phantom.

•“European Guidelines on quality criteria for diagnostic radiographic images”

•Data analysis : SPSS (SPSS Inc, Chicago, USA) 22.0

§ Scoring

• clearly inferior(VGA -2), slightly inferior (-1),

• equal to (0),

• slightly superior (+1), clearly superior (+2).

Materials & Methods

Image criteria description

§ Visually sharp reproduction of

• the vascular pattern in whole lung, particularly the peripheral vessels

• The trachea and proximal bronchi

• The borders of the heart and aorta

• The diaphragm and lateral costo-phrenic angles

§ Visualisation of

• the retrocardiac lung and mediastinum

• the spine through the heart shadow

• Hilar region

Materials & Methods

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Materials & Methods

§ Basic beam quality(kVp, mAs, HVL)

SID (cm)

Tube voltage (kVp)

Exposure current(mAs)

Exposure time(msec)

HVL (mmAl)

160 121.7±0.67 3.52±0.01 11.33±0.58 5.08±0.02

180 120.2±0.10 4.41±0.03 13.77±0.11 5.21±0.03

200 120.7±0.67 5.33±0.04 16.66±0.11 5.25±0.04

220 121.5±0.59 6.46±0.05 20.18±0.17 5.26±0.02

240 122.1±0.70 7.71±0.02 24.07±0.06 5.29±0.02

260 122.3±0.26 9.16±0.02 28.62±0.06 5.31±0.03

280 122.5±0.26 10.65±0.02 33.29±0.06 5.33±0.02

300 121.5±0.23 12.38±0.05 38.69±0.17 5.36±0.04

320 121.8±0.66 14.52±0.02 45.37±0.06 5.38±0.01

340 121.2±0.46 16.47±0.02 51.48±0.06 5.43±0.03

Results & Discussion

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§ Assessment of digital image quality

SID (cm) SNR Relative SNR180 6.05 100 220 5.50 90.85 260 5.59 92.37 300 5.55 91.77 340 5.24 86.65

Results & Discussion

① SNR

•SID 260 cm ∼ 300 cm : 5.56( -8.04%)(p=0.000)

•A SNR in the range 5 to 7 has been reported to be adequate for many imaging tasks.

•Rose Criterion (Albert rose) : SNR ≥ 5

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Materials & Methods

SID FOM Relative FOM

180 132.96 100

220 117.24 88.18

260 126.13 94.87

300 128.57 96.70

340 119.30 89.73

Results & Discussion

② FOM

• SID 260 cm ∼ 300 cm : 127.03(- 4.46%)(p=0.000).

• Higher values of the FOM indicate the ability of a system to deliver better

performance in terms of SNR at a lower dose to the patient.

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SID(cm) CL+CR(mm) TD(mm) CTR(%)

180 119.98 293.42 40.89

220 119.35 290.35 41.11

260 119.02 287.87 41.35

300 118.59 286.12 41.45

340 118.16 284.46 41.54

③ Cardio-thoracic ratio (CTR(%) & Cardiac diameter(mm)

• Chest radiography is the most commonly used modality for the detection of

cardiomegaly and the evaluation of CTR.

• This values are necessary for a better and more accurate evaluation of

cardiovascular diseases.(“Danzer” was the first to describe the CTR)

Results & Discussion

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Materials & Methods

§SID 180 cm §SID 220 cm

§SID 300 cm§SID 260 cm

Results & Discussion

④ VGA

• No statistical differences were seen for VGA scores according to SID

changes(p=0.338).

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Materials & Methods

§ Dosimetry

SID (cm) ESD (mGy) Relative ESD

180 0.2718 100

220 0.2576 94.78

260 0.2474 91.02

300 0.2397 88.19

340 0.2303 84.73

Results & Discussion

① ESE / ESD (mGy)

• Statistically significant difference were ESAK according to SID changes(p=0.000).

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② ED (mSv)

SID (cm)ED (mSv)

ICRP 60 ICRP 103180 0.0739 0.0786

220 0.0725 0.0771

260 0.0720 0.0766

300 0.0711 0.0752

340 0.0690 0.0731

Results & Discussion

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Effective dose (mSv)

SID (cm)

Activebone

marrowColon Liver Lungs Prostate Stomach Thyroid Urinary

bladderWeighted remainder

180 0.0922 0.0136 0.1237 0.2148 0.0001 0.0762 0.0210 0.0010 0.0699

200 0.0908 0.0145 0.1214 0.2103 0.0003 0.0754 0.0220 0.0008 0.0680

220 0.0898 0.0147 0.1197 0.2078 0.0011 0.0767 0.0240 0.0008 0.0670

240 0.0892 0.0144 0.1195 0.2037 0.0001 0.0780 0.0223 0.0010 0.0673

260 0.0889 0.0141 0.1188 0.2029 0.0001 0.0776 0.0197 0.0013 0.0665

280 0.0881 0.0139 0.1184 0.1998 0.0001 0.0764 0.0194 0.0013 0.0655

300 0.0876 0.0144 0.1157 0.1980 0.0001 0.0747 0.0208 0.0010 0.0655

320 0.0861 0.0145 0.1144 0.1940 0.0001 0.0754 0.0212 0.0013 0.0649

340 0.0849 0.0151 0.1135 0.1920 0.0000 0.0744 0.0222 0.0012 0.0636

② ED (mSv)

Results & Discussion

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Stochastic radiation risks

§ Asian mortality data(30.0 year-old male)

§ 한국 표준체격(남) : 167cm/63.8kg SID 180 cm SID 260 cm SID 300 cm

§ Expected length of remaining life 46.0 years 46.0 years 46.0 years

§ Risk of exposure-induced cancer death (REID) 3.79E-06 3.53E-06 3.45E-06§ Cancer mortality for other causes;

not related to this exposure21.40% 21.40% 21.40%

§ Loss of life expectancy (LLE) 0.9 hours 0.7 hours 0.7 hours

§ Cancer type REID REID REID

• Leukemia 5.2E-07 2.9E-07 2.8E-07

• Colon cancer 5.5E-08 5.9E-08 6.2E-08

• Liver cancer 6.7E-07 6.7E-07 6.5E-07

• Lung cancer 1.8E-06 1.6E-06 1.5E-06

• Stomach cancer 3.6E-07 3.8E-07 3.7E-07

• Bladder cancer 1.5E-09 1.9E-09 1.9E-09

• Other cancer 5.4E-07 5.2E-07 5.2E-07

Results & Discussion

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Conclusion

SID (cm)

SNR FOM CTR(%)

Cardiac diameter(mm)

180 6.054 - 132.96 - 40.89 - 119.91 -

240 5.506 -9.05% 119.75 -9.93% 41.23 -0.81% 119.32 -0.49%

280 5.555 -8.24% 126.49 -4.87% 41.43 -1.3% 118.93 -0.82%

320 5.360 -11.46% 122.37 -7.96% 41.48 -1.43% 118.24 -1.39%

• In the case of SNR, 240 cm, 280 cm, and 320 cm were 9.05%, 8.24%, and 11.46%

respectively decreased especially, by 8.03% between SID of 260 cm and 300 cm, but SNR

was 5.24 up to 340 cm.

• In the case of FOM, 9.93%, 4.87%, and 7.96% were respectively decreased especially, by

4.33% between SID of 260 cm and 300 cm.

• There were no significant differences in VGA thus the image is valuable in diagnosis.

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Conclusion

SID (cm) ESD (mGy)ED (mSv)

ICRP103 Lung

180 0.236 - 0.074 - 0.215 -

240 0.215 -8.7% 0.072 -2.42% 0.204 -5.17%

280 0.209 -11.47% 0.071 -4.1% 0.199 -6.98%

320 0.207 -13.6% 0.069 -5.58% 0.194 -9.68%

• In the case of ESD, 240 cm, 280 cm, and 320 cm were 8.7%, 11.47%, and 13.56%

respectively therefore significant reduction was confirmed.

• In the case of ED, 2.89%, 4.67%, and 6.41% in the body and 5.08%, 6.09%, and 9.6% in

lung were reduced.

• It is predicted that increasing SID up to 300 cm in digital chest radiography can

reduce patient dose without decreasing image quality.

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