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.

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

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

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!

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

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

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

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

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.

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

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

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

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. مناسب، كاف، مقبول يحافظ على

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.

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.

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.

Floor is open for Questions and Discussion Thank you