Patient data acquisition and treatment verification in radiotherapy.

1. PATIENT DATA ACQUISITION
AND TREATMENT
VERIFICATION
JULIYET K JOY

2. NEED FOR PATIENT DATA
 Within the treatment simulation and calculation process, the
patient anatomy and tumour targets have to be represented
by a model for the patient.
 Nowadays such model is 3-dimensional model.

3. DATA'S ARE
 Contour outline
 Density of relevant internal structures
 Location and extent of target volume
 Final accuracy of treatment plan is strongly dependent on the
availability of patient data
 The amount of required patient data depends on:
- The treatment planning method/system
- the dose calculation method

4.  The patient information required for treatment planning varies
from rudimentary to very complex data acquisition:
 Distances read on the skin.
 Manual determination of contours.
 Acquisition of CT information over a large volume.
 Image fusion (also referred to as image co registration)
 using various imaging modalities, such as CT, MRI, and PET.
 Advanced methods in IGRT

5. BODY CONTOURS
DATA FOR 2D TREATMENT PLANNING
 Manual contour
making: A single patient
contour, acquired using lead
wire or plaster strips, is
transcribed onto a sheet of
graph paper, with reference
points identified.

6. POINTS TO BE CONSIDERED
a) Patient contour must be obtained with the patient in the same
position as used in the actual treatment.
b) A line representing the tabletop must be indicated in the contour
so that this horizontal line can be used as a reference for beam
angles.
c) Important bony landmarks as well as beam entry points must be
indicated on contour.
d) Checks of body contour are recommended during the treatment
course if the contour is expected to change due to reduction of
tumour volume or a change in patient weight.
e) If body thickness varies significantly within the treatment field,
contours should be determined in more than one plane.

7. INTERNAL STRUCTURES
• Localization of internal structures for treatment planning provide
quantitative information in regard to the size and location of
critical organs and in homogeneities.
• Qualitative information can be obtained from diagnostic
radiographs.
• Devices used in modern times for the localization and the target
volume are
 CT (Computed tomography)
 MRI(Magnetic resonance imaging)
 Ultrasound

8. CT
• The internal structure of an
object can be reconstructed
from multiple projections of
the object.
• The ray projection are
formed by scanning a thin
cross section of a body by
narrow x-ray beam and
measuring the transmitted
radiation with sensitive
radiation detector.

9. • The detector does not form image.
It adds up energy of all
transmitted photons.
• The numerical data are computer
processed to reconstruct image.
• Modern scanner:X-ray tube rotates
within a stationary circular array of
1000 or more detectors.
• Representation of attenuation
coefficients constitutes a CT
image.
• In a spiral or helical CT scanner
the X-ray tube spins axially around
the patient while the patient is
translated longitudinally through
the scanner aperture.

10. CT NUMBER
 The reconstruction algorithm
divides each axial plane into
small voxels,and generates CT
numbers.
 Which are related to calculated
attenuation coefficient for each
voxel.
 The actual image created CT is
actually made up of thousands of
square , this square arrangement
of square is other wise called
matrix.

11. CT NUMBER
 The Hounsfield unit is a way to characterize
radiation attenuation in different tissues.
 It is a quantitative scale for describing radio
density and is frequently used in CT scans,
where its value is also termed CT number.
 The CT scanner calculates, from the
collected data, linear attenuation coefficient
(µ).
 After the CT computer calculates a value for
the linear attenuation co-efficient of each
pixel the value is converted to a new
number called “CT NUMBER”

12.  Hounsfield numbers(H):
 Each pixel in reconstructed image is assigned a CT number or Hounsfield
unit(HU) between +1000 to -1000, depending upon the amount of the
absorption within that block of tissue.
 The use of the CT number is to measure tissue density that can aid
radiologists in the interpretation of images and diagnosis of disease.

13. CLINICAL SIGNIFICANCE OF CT
NUMBER
 CT number values are clinically
relevant in determining the
composition of various tissues in
the body.
 To evaluate things that do not
have a specific structure – a
rounded tumour could be made
of fat or not – benign or
malignant. Fluid filled spaces,
for example cysts, could contain
water or have an attenuation
corresponding to blood.
 Non linearity caused by change
in atomic number of tissues,
which affects the proportion of
beam attenuation by Compton
versus photoelectric interactions

14. TREATMENT PLANNING CT SCANS
 A flat table top should be used
 A large diameter CT aperture(e g: ≥70cm)
 Care should be taken to use patient positioning or immobilization
devices that do not cause image artifacts.
 Patient positioning,leveling and immobilization should be done in
accordance with the expected treatment technique.
 External contour landmarks can be delineated using radiopaque
markers such as plastic catheters.
 Image scale should be accurate both in the X and Y direction.

15. 3-D TREATMENT PLANNING
 The interslice distance must be sufficiently small to
accurately reconstruct the image in three dimensions
 Depending on the tumor site or the extent of
contemplated treatment volume, contiguous scans are
taken with slice thickness ranging from 1 to 10 mm. The
total number of slices may range from 30 to over 100.
 3-D planning has been shown to be useful and practical
for most tumor sites (e.g., head and neck, lung, and
prostrate)
 Treatment of well-localized small lesions (e.g., <4 cm in
diameter) in the brain or close to critical structures by
stereotactic radiosurgery has greatly benefited from 3-D
planning.
 Brachytherapy is amenable to 3-D planning because of
the limited number of slices involving the target.

16. MRI
 Magnetic resonance imaging(MRI) is a technique
that uses a magnetic field and radio waves to
create detailed images of the organs and tissues
within your body.
 Basic Physics of MRI involves nuclear magnetic
resonance(NMR).

17. MECHANISM
 Magnetic field temporarily realigns hydrogen atoms in your
body.(Hydrogen nucleus[single proton] present in water
molecules and in all body tissues.)
 The hydrogen nuclei partially aligned by a strong magnetic
field.
 The nuclei can be rotated using radio waves and they
subsequently oscillate in the magnetic field while returning to
equilibrium.
 Radio waves cause these aligned atoms to produce signals
and is detected by antennas(coils)
 Signals used to create cross-sectional MRI images.

19. COMPONENTS
 Static magnetic field
coils
 Gradient coils: used to
produce deliberate
variations in the main
magnetic field. 3sets
one for each direction.
 RF(radiofrequency)coil
s: transmitter and
receiver.

20. FUNCTIONAL MRI
 FMRI based on same MRI technique
 Detects changes in blood flow
 Technique for measuring brain activity
 It works by detecting the changes in blood oxygenation and
flow that occur in response to neutral activity
 Used in the study of brain function, applications in the field of
cognitive neuroscience, and in radiotherapy treatment
planning to avoid irradiating critical functional regions at risk in
the brain

21. MAGNETIC RESONANCE SPECTROSCOPY
IMAGING
 Technique that allows the study of metabolic changes in
various tissues of the body
 Used to detect and analyze signals from number of chemical
nuclei such as hydrogen,carbon,phosphorus,sodium,flurine
 Study of metabolites by analyzing different peaks in the MR
spectrum
 In radiotherapy MRS imaging used to characterize between
prostrate and brain tumours

23. ULTRASOUND
 Ultrasound imaging, also called sonography,involves
exposing part of the body to high frequency sound
waves(>20000Hz) to produce pictures of the inside of the
body.
 Do not use ionizing radiations
 It provide information's in localizing many malignancy prone
structures in the lower
pelvis,retroperitoneum,upperabdomen,breast,and chest wall
 Application in radiotherapy: ultrasound guided prostrate
implant

24.  Ultrasound used to produce images either by transmission or
reflection
 Ultrasonic waves reflected from different tissue interfaces
 The reflections/echoes are caused by variations in acoustic
impedance(Z) of materials of opposite sides of the interfaces
 Larger the difference in Z between two media, greater the
fraction of ultrasound energy reflected at the interface
 Eg:air-tissue,tissue-bone and chest wall-lung,strong
reflections of ultrasound.
 Image by attenuation
 It is characterised by attenuation coefficient, attenuation
coefficient for ultrasound is very high for bones compared with
soft tissue

25.  Ultrasonic waves generated as well as detected by ultrasonic
probe / transducer
 An ultrasonic transducer converts electrical energy into
ultrasound energy, and vice versa
 Accomplished by a process known as piezoelectric effect.
 Inside the probe piezo eclectic crystals are placed, most
common crystals are barium titanate,lead metaniobate
 Display modes:1)A(amplitude)mode
2)B(brightness)mode
3)M(motion)mode
 In radiotherapy, the cross-sectional information used for
treatment planning is exclusively derived from the B scan
images

26. TREATMENT VERIFICATION
 All radiotherapy involves risk because even small error in
treatment planning, delivery or dosimetry can lead to negative
consequences.
 Human body is complex organism and tumours often located
close to the normal tissues and OAR
 So ensuring that the right radiation dose has been given to the
right place.
 Patient presents clinical challenges everyday
 Set-up difficulties
 Soft tissue deformation
 Irregular respiration
 Spontaneous motion

27. Verification can be done by
1)PORTAL FILMS
2)ELECTRONIC PORTAL IMAGING
3)CONE-BEAM CT

28. PORT FILMS
 A port film is an X-ray taken at the beginning of a radiation
treatment, and once a week during your therapy to ensure
proper radiation positioning. Port films are done to make sure
that patient and the radiation machine are properly aligned to
each other.
 Port films will determine if there have been any changes in the
size, shape, or location of your radiation treatment field to
ensure that the therapy is both effective and safe.
 Disadvantages:
 Poor image contrast due to high beam energy(>10mv),large
source size(co-60),large patient thickness.
 Slow acquisition time
 Image enhancement not possible
 Storage problems

29. ELECTRONIC PORTAL IMAGING
 Allow real time verification of
patient setup
 Acquisition time short
 Multiple images possible
 Reasonable image quality
 Software assisted image
enhancement
 Online corrections possible

30.  The first EPID system was
video based.
 The beam transmitted through
the patient excite a metal
fluorescent screen.
 A front silver mirror, placed
diagonally, reflects the
fluorescent light by 90º into the
video camera.
 The analog output of the video
camera is converted into a
digital array with a frame
grabber for digitalizing the
video image

31.  Another type is matrix ionization chamber system that
consist of 256*256 liquid ionization chamber containing an
organic fluid and a microcomputer for image processing.
 Most commercial EPIDs use flat panel arrays of solid state
detectors based on amorphous silicon (a-Si) technology.
 Scintillator converts the radiation beam into visible photons.
 The light is detected by an array of photodiodes implanted on
an a-Si panel.
 The photodiodes integrate the light into charge captures.
 a-Si is used because of its high resistance to radiation
damage.
 Resolution and contrast is greater than the other systems.

32. CONE-BEAM CT
 Cone beam CT scan is the CT
scans with detectors imbedded
on a flat panel instead of
circular ring.
 In CBCT, planar projection images are obtained from multiple
directions as the source with the opposing detector panel
rotates around the patient through 180 degrees or more.
 These multidirectional images provide sufficient information to
reconstruct patient anatomy in three dimensions, including
cross-sectional, sagittal, and coronal planes.

33. KILOVOLTAGE CBCT
 Kilovoltage x-rays for a kilovoltage CBCT(kVCBCT) system are
generated by a conventional x-ray tube that is mounted on a
retractable arm at 90 degrees to the therapy beam direction.
 The imaging system is capable of cone beam CT as well as 2-D
radiography and fluoroscopy.
 Advantages: a)ability to produce volumetric CT images with good
contrast and submillimeter spatial resolution.
b)Acquire images in therapy room coordinates
(c) Use 2-D radiographic and fluoroscopic modes to verify portal
accuracy, manage patient motion, and make positional and
dosimetric adjustments before and during treatment.

34. MEGAVOLTAGE CBCT
 Megavoltage CBCT (MVCBCT) uses the megavoltage x-ray
beam of the linear accelerator and its EPID mounted opposite
the source.
 EPIDs with a-Si flat panel detectors are sensitive enough to
allow rapid acquisition of multiple, low-dose images as the
gantry is rotated through 180 degrees or more. From these
multidirectional 2-D images, volumetric CT images are
reconstructed.
 MVCBCT system has a reasonably good image quality for the
bony anatomy and, in some cases, even for soft tissue
targets.
 MVCBCT is a great tool for on-line or pretreatment CT,
avoidance of critical structures such as spinal cord, and
identification of implanted metal markers if used for patient
setup.

35. ADVANTAGES OF MVCBCT OVER KVCBCT:
 Less susceptibility to artifacts because of high-Z objects such
as metallic markers in the target, metallic hip implants, and
dental fillings
 No need for extrapolating attenuation coefficients from
kilovoltage to megavoltage photon energies for dosimetric
corrections

37. THANK YOU