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Comparison Of Radiation Dose And Procedure Time Between Fluoroscopic Guidance And CT Guidance For Lumbar Puncture 2013

Category Interventional Todd Miller
Allan Schoenfeld
Allan L. Brook
Purpose The purpose of this study was to compare procedure times and radiation dosages for lumbar punctures performed with fluoroscopic guidance and CT guidance. Materials & Methods This was an IRB approved and HIPAA compliant retrospective data review.  45 consecutive patients who had lumbar punctures with CT guidance and 100 consecutive patients who had lumbar punctures with fluoroscopic guidance were included.  There were no exclusions.  Procedures were judged technically successful if CSF was obtained.  Procedure time was measured for the CT guided procedures using the PACS time stamp on the scout image and the PACS time stamp on the last helical image in the last series of the procedure when CSF was obtained.  Needle distance was measured from the skin surface to the needle tip on the image where CSF was obtained.  Needle angle was measured from the final image on the PACS workstation.  For the fluoroscopically guided procedures nursing notes were utilized to determine the time of skin prep and when CSF access was obtained.  DAP and total fluoroscopy time was recorded for each procedure. For CT, dose was calculated from DLP in the dose report displayed the CT machine.  The DLP was multiplied by a conversion factor, which was calculated using the technique described previously. 12 Briefly, a conversion factor chart was created using a Monte Carlo calculation (ImPACT CT Patient Dosimetry Calculator, version 1.0.2, http://www.impactscan.org/).  ED per DLP (ED/DLP) constants ranged from 11-18 µSv/mGy-cm over the distance from L1 to L5 (stations 10-30 on the ImPact Phantom).  The average and median ED/DLP constant was 14.5 µSv/mGy-cm.  This was used to calculate ED for the scan volume used during the procedure.  Fluoroscopic dose was obtained from the procedure report where fluoroscopic time and DAP were reported.  Published conversion factors were used to establish effective dose.   PCXMC Version 2.0.1.3 (STUK – Radiation and Nuclear Safety Authority Helsinki, Finland) software was also used to simulate fluoroscopic guidance for LPs for a representative sample of the patients in the series.  This was used to generate effective dosages expected over a range of field sizes and imaging times.  Medical records including the procedure report, nursing notes, and follow-up office notes were reviewed for information on complications categorized according to SIR recommendations. Results A total of 45 patients had CT guided CSF access procedures (31 LPs, 8 myelograms, 2 Morphine test injections and 4 lumbar drain placement).  During the first six months of the data collection period a consecutive cohort of 100 fluoroscopically guided lumbar punctures was included.  For CT guidance 30 female and 15 male patients were included. The range ages of patients were 20-78 (Ave 49, SD 14). Twenty-four were obese with a BMI of 30 or greater (average 33.15, median 32.8, SD 12).  Eighteen had previous spinal surgery.  Common indications for LP included headache or pseudotumor, lumbar drain, myelography, failed bedside LP, and meningitis. Common indications for myelogram were severe back pain and radiculopathy. All procedures were successful with a single needle pass.  Half of the procedures utilized a 22g needle.  The average needle depth was 77.64mm (median 75, 45.7 - 127.3), with an average needle angle of 8.7 (range 1.5-24 degrees).  Procedure time averaged 14 minutes (range 5 to 42 minuets) with a mean ED of 1.98 mSv (median 1.71, 0.20-8.18) as shown in Figure 2.   Average DLP was 120 mGy-cm (median 112, 39-211).  Procedure time and ED for uncomplicated patients by experienced operators was 11 minutes and 1.4 mSv. There were no immediate or delayed complications.  34 CSF sample results were available for review.  Two were from lumbar drain placements (RBC 80,000 and 640,000), and one was in a patient with new viral meningitis (RBC 21,930). Average RBC count in the remaining 31 samples was 97 (median 8, 0-1720).  One sample exceeded the cutoff of 1000 RBC used to discriminate traumatic tap from aneurysmal subarachnoid hemorrhage.  No patients experienced a prolonged or new low-pressure headache after the procedure (lumbar drain patients excluded). For fluoroscopic guidance 68 female and 32 male patients were included. The ages of patients were 18-88 (Ave 47, SD 17). 51 were obese with a BMI of 30 or greater (average 31.3, median 29.88, SD 9).  Common indications for LP included headache or pseudotumor, myelography, failed bedside LP, and meningitis.  All procedures were successful with a single needle pass.  Half of the procedures utilized a 22g needle.  Procedure time averaged 12 minutes (range 12 to 30 SD 6) with a mean DAP 10 (0.1-70, SD 11).   Fluoroscopic times averaged 1.3 minutes (SD 1.15, median 1.1).  There were no immediate or delayed complications.  74 CSF sample results were available for review.  Average RBC count 183 (median 3, 0-2300, SD 512).  Four samples exceeded the cutoff of 1000 RBC used to discriminate traumatic tap from aneurysmal subarachnoid hemorrhage.  Two patients experienced a prolonged or new low-pressure headache after the procedure.  These were both successfully treated with epidural blood patch with CT guidance. Effective dosages for fluoroscopic procedures were estimated using the PCXMC software.  Effective dosages based on field size AP 10x10 cm, 14x14 cm, 20x20 cm, 30 x 30 cm and 10x10 cm, 20x20 cm, 30 x 30 cm lateral projections and one minute of total fluoroscopy were used to generate values.  Results are included as a table.  Effective dosages for fluoroscopic procedures were estimated using the PCXMC software.  Effective dosages based on field size AP 10x10 cm, 14x14 cm, 20x20 cm, 30 x 30 cm and 10x10 cm, 20x20 cm, 30 x 30 cm lateral projections and one minute of total fluoroscopy were used to generate values.   Average total effective dosages ranged from 0.54 to 8.19 millisieverts/minute (average 2.9) Conclusion Average procedure times from skin prep to initial CSF sample was similar for CT guidance and Fluoroscopic guidance (12 minutes Fluoroscopic, 14 minutes CT) and effective dosages were about equal (2 millisieverts CT guidance and 2.7 milliseiverts Fluoroscopic guidance).   References 1. 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