1. Radiological Sciences Department Ph.D., Paris-Sud 11 University
Radiotherapy Physics and Equipment
RAD 481
Lecture’s Title: Clinical and Imaging localization
Dr. Mohammed EMAM
Ph.D., Paris-Sud 11 University
Vision :IMC aspires to be a leader in applied medical sciences, health care education and research.

2. Localization
The target volume and critical normal tissues are delineated with respect to patient’s external surface contour.
What to localize?
Tumor
Organ
Methods?
Clinical examination
Imaging

3. Why Localize? Irradiate the tumor and spare the normal tissue.
Allow calculations and beam balancing.
Define radiation portals.
Use the beam directing devices.

4. Clinical localization
Advantages:
Available everywhere.
Cheapest and quickest(?).
Needs little additional equipment.
Disadvantages:
Error prone in the wrong hands.
Accessible areas required.
Volumetric data not easily obtained.
Clinical localization is mandatory despite advanced imaging – need to know what to image!

5. Imaging Localization Imaging: Type of study selected depends on:
X-rays:
Plain
Contrast Studies
CT scans
MRI scans
USG scans
PET scan
Fusion imaging
Type of study selected depends on:
Precision desired.
Cost considerations
Time considerations
Labour considerations
جهد او عمل شاق

6. X rays The most common and cheapest modality available.
However 2-D data acquired only.
Orthogonal films can be used with appropriate contrast enhancement for localization in 3 dimensions.
متعامد

7. Estimation of depth From data gained by localization studies:
CT / MRI – Accurate data
Lateral height method
Tube shift method
Depth estimation necessary for:
Calculations
Selection of beam energy
جانبي

8. Lateral height method d H2 H1
H1 + H2 2
d = d

9. Tube shift method
Image shift and tube shift are interrelated WHEN the tube to target distance remains constant.
Goal: To obtain a graph of different object heights against the tube shift.
Serial measurements of image shift measured (for same tube to film distance) while varying the height of the markers above the table.

10. Tube shift principles S f
Marker
Tumor d2 y d1 x1 x2

11. Calculation y y S x1 d1 = S f – d1 Marker x2 d2 Tumor = f S f – d2 =
d2 – d1 d1 = f
x2 + S x2 -
x1 + S x1 x1 x2

12. CT scans
Provides electron density data which can be directly used by the Treatment Planning System (TPS).
Volumetric reconstruction possible.
Good image resolution - better where bony anatomy is to be evaluated.
The image is a gray scale representation of the CT numbers – related to the attenuation coefficients.
Hounsfield units =
(μtissue – μwater) x 1000/ (μwater)
253
265
235
125
112 56
450
156
135
158
247
269
300 65 36
123
598

13. CT scan perquisites Flat table top
Large diameter scan aperture (≥ 70 cm).
Positioning, leveling and immobilization done in the treatment position.
Adequate internal contrast – external landmarks to be delineated too.
Preferably images to be transferred electronically to preserve electron density data.
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14. MRI scans Advantages: Disadvantages:
Imaging in multiple planes without formatting.
Greater tissue contrast – essential for proper target delineation in brain and head and neck
No ionizing radiation involved.
Disadvantages:
Lower spatial resolution
Longer scan times
Inability to image calcification or bones.

15. Fusion Imaging Includes PET – CT imaging and Fusion MRI.
Allows “biological modulation” of radiation therapy.
Technology still in it’s infancy – (?) The future of radiotherapy.

16. Fusion Imaging Includes PET – CT imaging and Fusion MRI.
Allows “biological modulation” of radiation therapy.
Technology still in it’s infancy – (?) The future of radiotherapy.

17. Floor is open for Questions and Discussion
Thank you