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How Does Patient Radiation Exposure Compare withLow Dose O-Arm vs. Fluoroscopy

for Pedicle Screw Placement?

a,bAlvin W. Su, MD, PhD; a,cAmy L. McIntosh, MD aAnthony A. Stans, MD; aA. Noelle Larson, MD

aDept. Orthopedic Surgery, Mayo Clinic, Rochester, MNbSchool of Medicine, National Yang-Ming University, Taipei, TaiwancDept. Orthopedic Surgery, Texas Scottish Rite Hospital for Children, Dallas, TX 

International Congress on Early Onset Scoliosis

November 19 & 20, 2015

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Background: Pedicle Screw Instrumentation

I. O-arm (intra-OP CT scan)A. reported to improve screw accuracy [1-2]

B. “pediatric protocol” minimizes radiation dose [3-4]

II. C-arm (intra-OP fluoroscopy)A. well-establishedB. radiation dose has high variability [5-7]

1Ledonio+ JBJS-Am 2011; 2Larson+ JPO 2012; 3Abul-Kasim+ J Spinal Disord Tech 2012; 4Su+ JPO 2015; 5Nelson+ Spine J 2013,;o+ JNS-Spine 2014; 7Kuhne+ SOMOS 2014

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HypothesisPatient radiation exposure with C-arm

technique is comparable to low-dose O-arm for pedicle screw placement

Motivation1. Does O-arm really generate more radiation?2. Is O-arm safe for the young patients?

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Matched-control cohorts: O-arm vs. C-arm

year 2014 O-arm C-arm p value

n 14 14 n/a

DiagnosisAIS (12), JIS

(2)AIS (12), JIS

(2)n/a

Age (years)

13 (11-18) 14 (12-18) 0.09

B.W. (kg) 57 (48-80) 58 (43-86) 0.60

Imaged levels

11 (6-15) 11 (5-13) 0.57

data: medium (range); t-test

Aim: Compare total effective dose (ESum) btw. O-arm vs. C-arm

two centers, both IRB approved

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O-arm® (Stealth, Medtronic)

1Abul-Kasim+ J Spinal Disord Tech 2012; 2Su+ JPO 2015; 3ICRP 103 2007;

O-arm effective dose = 0.65 mSv / scan

Chest PA:0.02−0.10

mSv[3]80 kV, 20 mA, 80 mAs [1,2]

1x

7x

Pedslow-dose

Defaultprotocol

Effective Dose

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C-arm total effective dose by ratio of T:L, AP:LAT

1Abul-Kasim+ J Spinal Disord Tech 2012; 2ICRP 103 2007

GE OEC 9900 Elite® mobile C-arm

Phantom: T7 & L3, AP & LAT

Thoracic9 levels

Lumbar2 levels

Ex: If we image T4−L2

total image time partitioned to T & L spine converted to effective dose [1-2]

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Results: Fluoroscopy time is variable

• total 26 O-arm scans• two scans (n=10)• one scan (n=4)1 spin / 6 levels

• C-arm imaging time35 ± 24 sec

(7.9−75.0) ~19 sec / 6 levels

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ResultsO-arm resulted in higher (4X) total effective dose than C-arm

Chest PAX-ray

0.02-0.1 mSv

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Limitations: C-arm dose was approximated

• intra-OP radiographs not included

~ 0.2 (AP) & 0.7 (LAT) mSv [1]

1Luo+ Spine Deformity 2015; 2Brown+ Pediatr Radiol 2000 3Nawfel+ Radiology 2000; 4Perisinakis+ Radiology 2004

used phantom for C-arm dose: well recognized method for radiation dosimetry [2,3]

our conversion factors ~ literature reports [4]

AP+LAT1 set

Effective Dose

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Discussion: C-arm dose has high variability

• Varies with patient characteristics, C-arm device type/settings / preferences

• Depends on surgical technique/fluoroscopy times

• Effective dose reported as high as 2.92 mSv [1] (3x low-dose O-arm)

• Total fluoroscopy time can range from 63-126 sec [1,2]

(35 sec in our study)

1Perisinakis+ Spine 2004; 2Slomczykowski+ Spine 1999

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C-arm & pediatric O-arm are both “low dose”

• medical radiation exposure associated with cancer

• 100 mSv cumulative [4]

• 2.7x breast cancer death

• ICRP recommended occupational exposure

• < 50 mSv / year• < 100 mSv / 5 years

1Measurements NCoRP 2014; 2Ul Haque+ Spine 2006; 3Rampersaud+ Spine 2000; 4Doody+ Spine 2000

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Significance

• Pediatric orthopedic surgeons must be informed about radiation imparted to patients and surgical team

• One low dose O-arm = 85 s of C-arm spine fluoroscopy

• Total dose of C-arm depends on fluoroscopy time

• Both systems impart < 1 year annual background radiation to patient