8/12/2011. Calculating Patient-specific Skin Dose. Call to Action! Fluoroscopy time poor measure of PSD Outline

Transcription

1 Call to Action! Calculating Patient-specific Skin Dose William Pavlicek PhD Dept of Radiology Mayo Clinic Arizona 2011 MFMER slide MFMER slide-2 Fluoroscopy time poor measure of PSD Outline 1. Peak Skin Dose Defined 2. Conditions Likely to Result in High PSD 3. Calculating PSD with (some) DICOM info 4. Informatics Tools for PSD (Wednesday) 5. Take away points 300 patients 2011 MFMER slide MFMER slide-4 1

2 Fluoroscopic/Acquisition Exposure Air Kerma Kerma accumulated in air at a specific point K a,i incident air kerma * Units: gray (Gy) Without backscatter K a,ref commonly computed from P KA * ICRU Report 74, Patient Dosimetry for X Rays Used in Medical Imaging, MFMER slide-5 1. DEFINE Peak Skin Dose D skin,max the most highly-irradiated skin region Compute D skin from K a,i : Validated Vendor K a,r Backscatter Mass-energy absorption coefficient ratio tissue:air Table and pad attenuation Equipment/patient specific information Account for locations of the x-ray beam/patient Actual source-skin entrance distances 2011 MFMER slide-6 C-arm Reference Point Location Validate vendors K a,r K a,r total air kerma at the reference point 15 cm from isocenter toward x-ray tube Other reference points exist Computed by vendor from P KA Reference point ~ patient s entrance surface Defined by IEC (2000 and 2008) and FDA (2009) Isocenter 2011 MFMER slide MFMER slide-8 2

3 Correction factor for Acquisition exposure (fluoro correction may differ!) Measure Table and Pad Attenuation* Field size PMMA kv Air kerma (mgy) Machine Air kerma (mgy) Chamber Correction Factor 22 4 inches inches inches inches inches inches inches inches inches inches inches inches inches = / kv M 2o (mgy) M 2i (mgy) Table/Pad Transmission Factor Correction Factor to be applied to DSR = 83.01/ *fixed technique service mode 2011 MFMER slide MFMER slide-10 Backscatter Correction (ICRU) Tube voltage/kv Filte r Field 10cm x 10cm Field 20cm x 20cm Field 25cm x 25cm HVL/mm AI ICRU tissue ICRU tissue ICRU tissue mm Cu mm Cu mm Cu Example Simple Geometry K a,r = 5 Gy Machine correction = 0.85 BSF = 1.4 Tissue/Air = 1.06 Table/Pad = 0.7 Ref Pt/Skin = 0 PSD = 4.4 Gy Both Fluoro AND Acquistions are localized to one area! Mass Energy Absorption Coefficient: Tissue/Air 1.06 McParland BJR, 71(1998) 2011 MFMER slide MFMER slide-12 3

4 PSD (Gy) 8/12/2011 PSD versus K a,r PSD vs. Air kerma y = x y = 0.592x Physics Notes Under table fluoroscopy is most common gantry orientation Backscatter correction ~ negates table/pad correction Vendor K a,r commonly higher than your measurements * Localization takes some effort Air kerma (Gy) * nominal & x-ray field size agree MFMER slide MFMER slide-14 Nominal/X-ray Field Agreement MU WA HI KA Source to Detector (mm) Image Area Dose Product (dgy*cm 2 ) Intensifier Size (mm) Imager Pixel Spacing (mm) Collimator Left Vertical Edge Collimator Right Vertical Edge Collimator Upper Horizontal Edge Collimator Lower Horizontal Edge Distance Source to Isocenter Number of Vertical Pixels Number of Horizontal Pixels Vertical Distance (mm) Horizontal Distance (mm) Image Area (mm 2 ) Image Area at Reference Point (mm 2 ) Exposed Area at Reference Point (m 2 ) Exposed Area at Reference Point (mm 2 ) % Error 4.88% 5.05% 6.97% 7.75% Validate K a,r Tableside/Console shows K a,r (sums Fluoro and Acq, continuously updated) Console shows Exam Protocol K a,r for acquisitions as acquired. At completion, the Exam Protocol shows separate summed Fluoro and Acq K a,r PACs may show Exam Protocol (screen capture) DICOM RD SR shows Fluoro and Acq K a,r, but need a report reader *Acquisitions: Digital Spots, Cine, DSA (Rot Angio only in Exam Protocol) 2011 MFMER slide MFMER slide-16 4

5 2. Conditions for High(er) PSD Complicated Procedures > 3 Gy Long procedure due to complicated episode Lateral and steep angle projection procedures Large patient (~125+ Kg) Extended/high radiation use due lack of training High dose Protocols set as default Procedures Percent Renal Angioplasty (156) 8 Liver Chemoembolization (126) 10 TIPS (135) 21 GI Bleed Dx/Rx (94) 30 Uterine Fibroid Embolization (90) 30 Head Embolization (382) 61 Spine Embolization (24) 92 from Rad-IR Study Table 5, JVIR v14, June MFMER slide MFMER slide-18 Steep angles used with cardiac cath Skin Dose angled views and patient size (470 patients) Ken Fetterly, RSNA MFMER slide MFMER slide-20 5

6 Skin Dose Rate (mr/min) 8/12/2011 Approx 5% Cardiac Cath pts >125 kg Magnification - use (only) when needed! Female Male Dose Response with 20cm Acrylic Low Normal High Water-equivalent Thickness (cm) 2011 MFMER slide FOV Diagonal SIze (in) 2011 MFMER slide-22 Collimation Is Key! Poor Protocol: High DSA and Fluoro Rate < 1 Gy 1-2 Gy 2-3 Gy 3-4 Gy 4-5 Gy 5-6 Gy 6-7 Gy 7-8 Gy 8-9 Gy 9-10 Gy MFMER slide MFMER slide-24 6

7 Vas Aorta Arch / Carotids Upper Ext Chemo Embo Vas Arch / Carotids Vas Upper Ext Protocol Names: Mesenteric Variability Pulmonary enemy Pulmonary of quality! Vas IR Mesenteric Unit 1 Vas IR Pulmonary Unit 2 Vas IR Pulmonary Unit 3 Upper Extremities Mesenteric Tube Check Vas Upper Extremities Vas Mesenteric Aorta Pelvis / Peri Upper Extremity Vas Aorta Vas Pelvis Vas Upper Extremity Mesenteric Renal Lower Extremity Vas Mesenteric Vas Renal Vas Lower Extremity Chemo Embo IVC Renal Renal Vas IVC Vas Renal Vas Renal CO 2 / Gad DSA IVC Pulmonary TIPS Vas IVC Vas Pulmonary Fistulogram CO 2 / Gado Neuro Vas Fistulogram Pelvis Vertebroplasty Tube Check Vas Pelvis Perc Neph Dyna IVC Perivision Endoleaks Dyna Vas IVC Vas Perivision DynaCT Body PICC Line Singel Leg InSpace 3D Catheter Placement Vas Single Leg DynaCT Head Tube Placement General Dyna Cardiac Vertebroplasty Vertebroplasty Cardiac OLD GenDYNA DSA 0 2D/3D Calib BILATERAL PERI Physic's Testing 2011 MFMER slide Informatics Tools for PSD Calculation DICOM Dose Structured Reports Contains Fluoro, Acquisitions, Rot Angio, etc. Reports are separate Objects may or may not be sent to PACs Multiple vendors offering dose reports More Physics tools needed 2011 MFMER slide-26 DICOM RDSR Tag(Group,Element) NAME Value Dose Area Product Total (Gym2) Dose (RP) Total (Gy) Fluoro Dose Area Product Total (Gym2) Fluoro Dose (RP) Total Total Fluoro Time(s) Acquisition Dose Area Product Total (Gym2) Acquisition Dose (RP) Total 0040,A ,A ,A124 Irradiation Event UID ,1030 Performing Physician's Name Physician DICOM RD SR Patient having 287 separate events 2011 MFMER slide MFMER slide-28 7

8 FLUORO USE DICOM & Info Primary angle Secondary angle Fluoroscopy Event 1 Table Longitudinal Position Table Lateral Position Table Height PERP (mgy) Local dose skin System Architecture RIMS Fluoroscopy Event DICOM DICOM SR HL7 DSA USE Fluoroscopy Event 3 Fluoroscopy Event 4 Acquisition Event WAN DICOM, HL7 Gateway Knowledge Base Dosimetry Analyzer Exam Information Database Reporting & Alerting Module Dose Tracking System Acquisition Event s Acquisition Event Texts Acquisition Event MFMER slide MFMER slide-30 Informatics for FGI ID Gender Procedure KAP/air kerma (cm2) Number of the scans Number of Fluoro Peak skin dose Total area radiated (cm 2 ) Reporting Tools Accessible online Need statistics, charts and data view Auto-formatted, ready to distribute Test f IR Emobalization (non-neuro) Gy 1068 Triggers and Alert Tools db monitoring Messages sent by / text messaging 2011 MFMER slide-31 Table: 0.8; Machine : 0.8; BSF: 1.4 TAR: MFMER slide-32 8

9 QA Report: PSD Exceeding 3Gy PATIENT_NAME PATIENT_ID M/F AGE ACCESSION DICOM_EXAM_ID PSD EXAM_DATE TESTING^JOE M TESTY^SMITH M PHANTOM^JANE M TESTT^JOE M PHANTOMS^SMITH M TESTS^TEST M TESTIE^JOE F MFMER slide MFMER slide-34 Take Away Know/validate Fluoro and Acquisition K a,r Measure Table/Pad Transmission Promote software upgrades to DICOM Radiation Dose SR Review default Protocol settings for high F/s (DSA, Spots, or cine) or Fluoro Pulse/s Encourage collimation, not magnification Embrace Informatics! 2011 MFMER slide MFMER slide-36 9

10 Basic References Team Members and I Thank you! Yasaman Khodadadegan Dr. Brian Chong, MCA Dr. Eric Huettl, MCA Gene Stephen Sabyan, Paden, MS., MCA R.T. (R), MCA Dr. Kenneth Fetterly, MCR Dr. Steve Langer, MCR Dr. Beth Schueler, Dr. Richard Morin, MCR MCJ Dr. Kevin Nelson, MCJ Dr. Teresa Wu, ASU Dr. Muhong Zhang, ASU 2011 MFMER slide MFMER slide-38 10