A simplified model of a C-Arm fluoroscopy unit to calculate dose distributions of interventional cardiology procedures

Transcription

1 A simplified mdel f a C-Arm flurscpy unit t calculate dse distributins f interventinal cardilgy prcedures 1 st GEANT4 Australian Schl and User Wrkshp 2011, Wllngng Sacha Refshauge, Iwan Crnelius, Christian Langtn Discipline f Physics, Faculty f Science and Technlgy, QUT Institute fr Health and Bimedical Innvatin, QUT

2 Interventinal Cardilgy and C-Arm Unit Interventinal Radilgy C-Arm unit Uses images frm the C-Arm flurscpy unit t guide minimally invasive interventinal prcedures. Usually dne with narrw tubes called catheters, cntrlled by physician. The catheters lcatin can be determined frm the images. Used fr real-time imaging f a patient. Typically used fr interventinal prcedures such as catheter ablatin f cardiac arrhythmias and pacemaker implants. Cntains an X-ray tube (surce) and image intensifier, psitined ppsite. Capable f mving in t varius cnfiguratins t imprve imaging and reduce radiatin scatter. Radiatin awareness in interventinal radilgy, a key issue: Very nature requires physician t stand beside patient, receiving substantial dses. Dse up t 0.8mSv per prcedure has been recrded t the eye lense by Urbniene et al. Withut prper awareness and prtectin this can lead t cataracts. Unlike patient, medical staff are expsed t this dse n a daily basis Flurscpy-guided interventinal prcedures becming mre cmmn Typical C-Arm unit, Siemens Dses t eyes and extremities f medical staff during interventinal radilgy prcedures,urbniene et al. 2011

3 Radiatin Prtectin and Awareness Radiatin awareness training essential: Training fr Physicians Withut slid understanding f radiatin levels and hw C-Arm cnfiguratin affects this, physician essentially blind Training is mandatry Radiatin awareness can be imprved. Currently invlves: Passive detectrs that nly reveal dse at a single pint. Expensive C-Arm units running t shw real-time dse in systems such as DseAware. Reading lengthy bks that explain the thery and shw hypthetical radiatin maps under varius cnfiguratins. DseAware system: Staff Radiatin Dses in a Real-Time Display Inside the Angigraphy Rm, Sanchez et al Occupatinal radiatin dses in interventinal cardilgy: a 15-year fllw up, Van et al. 2006

4 Augmented reality allws fr virtual infrmatin t be verlaid n t a cntextual scene. Medical augmented reality slutins are becming mre cmmn (Samset et al). This technlgy culd aid in the training prcess by immediately shwing hw the changes made affect the dse distributin in the catheter labratry. Augmented Reality Augmented Reality in Surgical Prcedures, Samset et al. 2008

5 Aim Imprve radiatin training prcedures by creating a training tl that utilises cutting-edge augmented reality technlgy. A fcus n being: Rbust: t meet standards expected f a training tl Interactive: t increase invlvement and learning Graphical: t aid learning Enthralling: t pique interest Realistic: t allw cncentratin n the cre infrmatin Create a mdel f a C-Arm flurscpy unit (and surrunding bjects) in GEANT4 t get a 2D dse map f the rm under different cnfiguratins.

6 Apprach / Plan Develp a methd whereby a trainee can bserve the hypthetical dse in the rm in a nn-btrusive way. As part f the training curse, specific aspects f the C-Arm cnfiguratin are altered, changing the displayed isdse lines accrdingly. An imprtant aspect f this prject is the eventual augmented reality utput via a wall-munted display. The methd in which this is dne is demnstrated in the flw-chart belw. Camera recrds vide stream Sends vide stream t PC PC lads dse visualisatin simulated by GEANT4, depending n cnfiguratin PC detects marker/feature PC verlays visualisatin n vide stream Result is utput t display AR Training mck-up invlving a wall-munted display

7 GEANT4 C-Arm Simulatin: Gemetry Simplified mdel f C-Arm unit in GEANT4. Scring vlumes are at 100 cm frm the flr. Object Material Shape Dimensins (cm) Wrld Air Cube 360 x 360 x 360 Phantm Water Elliptical Tube Image Intensifier (length) x 32 (wide) x 20 (deep) Lead Cylinder 23 (length) x 11.5 (radius) Surce Lead Cube 15 x 15 x 15 Flr Shielding Lead Rectangular Cubid 360x360x2 Scring Vlumes (129600) SD Cube 1 x 1 x 1

8 Primary Beam / Cuts Primary Beam Parameters Particle Energy Initial Psitin Initial Directin Value Gamma 200keV 60cm frm patient Twards image intensifier/patient (RAO, LAO, AP) Range Cuts Particle Cut Length Energy Threshld in Water Gamma 100 um 1.11 kev Electrn 10 cm MeV Psitrn 1 mm KeV Prtn 1 cm 1 MeV

9 Methd fr Dse Calculatin

10 Result Dse map generated frm 5 millin primary particles Physician waist f 32x20 cm val verlaid n t map.

11 Result Threshlds: 77% - 85% 60% - 65% 50% - 53% Raw data with threshld levels Smthed data with threshld levels Smthed fr better representatin n the augmented reality display. Appears as less ambiguity.

12 AR Display Result RAO 40 LAO 40 AP

13 Study f Effect f Patient Obesity n Physician Dse Started with smaller cylindrical phantm. Testing shwed significant changes with different sized phantm. Paper by Van et al suggests up t 14x difference in scatter frm patient thickness. This led t further testing invlving changing patient height and thickness. Dcument by Ashwell et al demnstrates waist circumference t height rati (W/Ht) and hw it can be used as a weight indicatr. This led t the use f weight categries and ranges. Perfrmed tw tests t bserve hw patient gemetry affects physician dse. The first cnsiders using the average adult height btained frm ABS and varying the waist circumference t height rati (W/Ht). Secnd cnsiders maintaining a healthy W/Ht rati and varying height. Height Waist circumference Hw Australians Measure Up, ABS Influence f patient thickness and peratin mdes n ccupatinal and patient radiatin dses in interventinal cardilgy, Van et al Rati f waist circumference t height is strng predictr f intra-abdminal fat, Ashwell et al. 1996

14 Results Physician Waist Dse vs Phantm Waist Circumference t Height Ratis; Cnstant Height 1.2 Obese Physician Waist Dse per primary (pgy) Very Thin Very Thin Thin Thin Overweight Healthy Obese Overweight Healthy Male Female Waist Circumference t Height Rati f Phantm

15 0.8 Results Dse at Physician Waist vs Phantm Height; 0.48 W/Ht 0.7 Physician Waist Dse per primary (pgy) Height f Phantm (cm)

16 Cnclusin Seen where current training tls are lacking and hw they can be imprved. Shwn usefulness f an augmented reality slutin. Lked at hw patient thickness affects dse. This can be integrated in t the prpsed training tl.

17 Future Plans Mre detailed C-Arm and patient gemetry fr GEANT4. Allws fr mre accurate results. Pending technical drawings frm Philips. Verify the simulatin results experimentally using DseAware r passive detectrs (TLDs). Additin f a 3D camera t retrieve depth map f scene. This will allw visualised isdse lines t be ccluded by bjects in the rm. Multiple cameras. This will prevent the marker r feature frm being ccluded by the physician r ther peple present in the rm.