image processing in measurement guided radiotherapy and geometric accuracy
TRANSCRIPT
Image Processing in Measurement guided
Radiotherapy and Geometric accuracy
Anto Vaz SKovai Medical Center and
Hospitals
Presentation Outline
X-ray a Brief History- (5 slides)
Medical Imaging a Brief History - (11 Slides)
Radiation Oncology Facts and Time stamp- (10 Slides)
2-D, 3-DCRT, IMRT , IGRT ,SRS.. - (12 Slides)
Steps involved Radiotherapy - (12 Slides)
Quality Assurance in Imaging and Radiotherapy - (10 Slides)
Radiotherapy- Time Stamp 1895 - X-ray - Wilhelm Roentgen -
Time Stamp Continued….1896 - Radioactivity - Henri Bequerrel
Time Stamp Continued ….1900 - α and β rays - Ernest Rutherford
Time Stamp Continued ….1900 - Radium and Polonium - Marie
Sklodowska Curie
X-rays in Medical Field
Crookes Tube to produce X-ray
John Hall Edward used clinical in Jan 1896
Surgically used in Feb 1896
Marie Curie had her mobile X-ray Setup in world war
Helped Surgeons at the Warfront to quickly assess bones, joints, internal haemorrages
Medical ImagingX-ray Machine - 2 D Image
Computed Tomography - 3 D Image
Fluroscopy - 2 D Image mutiple frames / sec
2D Radiograph with X-rays
Why ?
Y- AxisX- Axis
2D Radiograph with X-rays
Why ?
Y- AxisZ- Axis
3 D Tomograph with X-rays = C.T.
Y- Axis X- Axis
Z - Axis
Digital Medical Imaging - Fact Time
● Dicom- Digital Imaging and Communications in Medicine
● Standardised and Formulised in 1980 by NEMA & ACR
● Common Language to be spoken about Medical Imaging throughout the World
● First version in 1993 and the latest version in 2011 and yet to continue
● What is it needed to be common about imaging ?
Digital Medical Imaging - contd...
1-bit 2-bit 4-bit
8-bit 24-bit 12-bit
So What ?● Human Eye is Capable of differentiating 32 Shades of Gray(25)
● Normal DisplayMonitor used in CT can distinguish 256 shades of Gray (28)
● Dicom Images contains information about 4096 shades of Gray (212)
● This value (4096 shades) is beyond Human Eye’s Perception
● Window Level narrows the range of shade to be viewed at one time ?
Digital Medical Imaging - Contd...
He is the Reason - !● Sir Godfrey Hounsfield - Father of
Computed Tomography● Deviced a setup which will take standard
X-ray all around a patient (1971) ● Combine them to form a 3 D information
inside the patient● Used a Roating X-ray Tube and a fast
computer to process the Image● Given different shades based on Density
of tissue (-1000 to 0 to 1000 HU)
Graphically it means
-500 to 200-200 to 100
25 to 40
25
HU value equates the Electron Density of the Tissue
When are we going - !
RadiotherapyStarted in 1896, Dr Emil Grubbe used X-ray to
Treat Cancer
Early 1920s Radioactive elements radium and polonium were used to produce cutaneous Burns
Low voltage X-rays were used to treat superficial Tumors
For Deep Seated Tumors X-rays of Million volts are needed
Radioactive isotopes like Co-60 Ir-192 Cs-137 are some of the widely used sources
Photons, Electrons, Protons, Neutrons and Heavy Ion Particles are now used
Machines in Radiotherapy
Machines in Radiotherapy
Machines in Radiotherapy
Machines in Radiotherapy
Machines in Radiotherapy
Machines in Radiotherapy
Radiation Biology
Study of effect of Ionizing Radiation in living organisms
Interaction happen with 10-13 of a second of the Exposure
Free Radicals will be produced in any organic medium
Changes will be produced at the DNA level ex single break, Double bond break
Normal cells has repairing capacity, cancer cells dont
Effect of Radiation is cummulative
Combine these two
Fractionated radiation treatment will lead cells to recover
Radiation PhysicsGamma and X-ray They will deposit
energy as they travel through any medium
Level of deposition of energy depends type of particle, Electron Density of the Medium
Linear Accelerator based Radiotherapy
Video
2-D Radiotherapy
Conformal Radiotherapy
3DCRT
IMRT
Intensity Modulated Radiotherapy Where we modulate the intensity of radiation using Multi Leaf Collimator
Multiple Beam (7-9 Beams)
Reduce the Radiation going to the Organ at Risk (Spine,Brainstem,Parotid,Lung,Heart,Kidney,Rectum & Bladder)
Contd….
IGRT
Image Guided Radiotherapy, will use either 2D(Xray) or 3D imaging (Cone Beam CT)
Linear Accelerators will have capability of doing a Xray and CT
Recent Development is Linac with MRI- !
Ensure the Efficiency of Treatment with the help of Imaging
Change in Anatomy can be found during treatment and corrected
IGRT
Stereotactic Radio Surgery (SRS)
ste·reo·tac·tic - A technique in which one can reach a point inside a frame using rigid Coordinate System (Cartesian or Polar), Usually the frame will be attached to Patient Head
Word coined in late 1940’s
SRS
Stereotactic Brain Surgery
Stereotactic Radio Surgery Stereotactic Breast Biopsy
SRSOriginally designed with an intention to be used as surgical
tool by LeksellLater on used extensively for Neuro OncologyIt is based on Polar Coordinates (Angle,Depth Anterio
Posterior Position)Proton was the first choice by Physicist Kurt Liden and
Radiobiologist Borje LarssonDue to complication in Sychrocyclotron, Leksell made
simple and practically effective Gamma- Knife with the same Centre of Arc Principle (Early 1950’s)
In 1953 Linear Particle accelerator developed parallelly at London with similar approach(4 MeV Electrons)
Late 1980’s Linear Accelerator based SRS started to take main stage
Gamma Knife
First Generation ‘B’ Helmet needs Manual Positioning of Patient -
Prone to Human Error‘B’ Helmet fitted with APS Robotic
system to position the Patient
Linac based SRS ( X knife)
Cone, Frameless SRSMicro MLC ,Frame Based SRS Cone,Frame Based SRS
What Now- ?
Steps Involved in RadiotherapyPositioning of
PatientImaging in CT
Treatment Planning
Image Fusion
Target Delineation
MR, PET, DSA & 4DCT
Plan EvaluationDosimetry Verification
Image Guidance
Treatment Delivery
Patient
Patient Positioning
Imaging in CT
Supportive Images
Digitally Subtracted Angiograph
M R IP E T
4D-CT
Image Fusion
Target Delineation
Treatment Planning
Plan Evaluation
Dosimetry - Verification
Image Guidance
Treatment Delivery
Pit Fall- !● Radiation Oncologist, Medical
Physicist , Dosimetrist, Radiotherapy Technologist,Nursing Staff,RSO,Service Engineers
● Qualified Skill Tank is a Must● Periodical Training & Skill
enhancement● Periodic Quality Assurance and
Control
Image Quality and Assurance● Apart from Periodic QA for
CT, Couch tilt and sag has to be Quantified (Tolerance=0.5 deg)
● Nominal Image slice Indice has to be verified, Images has to be taken with a slice thickness of <=0.7mm ( Normal Voxel size in dicom Voxel = 0.7cm X 0.7cm X 0.7cm)
● Verification of CT number should be done monthly as dose deposition is directly correleating to this parameter
● Spatial Resolution(High and Low Contrast), In Plane Resolution has to match manufacturer spec
Image Quality ….● Proper Selection of
Reconstruction Kernel will improve spatial Resoltuion
● FOV impacts greatly on the reconstruction Clarity . Smaller the FOV better the clarity
● Timed Automatic Contrast Injector is must to have a enhanced visualisation of CT. Delay Time of contrast should be verified
● Keep CT Gantry at 0’ and pitch should be less than 1.3
Image Quality ….● Perform MR QA with the suitable phantom
periodically if MRA is a mandatory for visualization
● Check Signal to Noise Ratio,Image Uniformity,Spatial Linearity
● Slice Profile and thickness plays vital role in SRS as the target volume could be as small as 0.5 cc Recommended <1mm(T1 post Contrast)
● When MPR (Multi Planar Reconstruction ) is being used, do verify the reconstruction process with a phantom for any possible distortion along y axis(Superio Inferior Direction)
● For Frameless SRS, doing a Planning MR will remove most of the uncertainties involved in image registration
Image Quality ….● If DSA is being used to
identify AVM and CCF the following parameters should be periodically reviewed
● Orthogonality of the C-arms,Couch Sag, Docking system and Regular Fluro parameters also to be verified
● Needle phantom can be used to verify orthogonality of the arms as a alternative method
Machines in Radiotherapy