بسم الله الرحمن الرحيمبسم الله الرحمن الرحيم

و قل رب زدنى و قل رب زدنى ﴿﴾علمًا�علمًا�

صدق الله العظيمصدق الله العظيم

Introduction to Radiotherapy

Dr. Ahmed Al Far, M.D.Professor of Radiation Oncology

RAD 461RAD 461

What is the Target VolumesWhat is the Target Volumes??

The Target Volumes

◘◘ Before Planning:

1. Gross Tumor Volume (GTV): primary tumor + any detectable metastases in LN

2. Clinical Target Volume (CTV): GTV + sub-clinical micro. disease

◘◘ During Planning:

1. Planned Target Volume (PTV): CTV + safety margin to account for movement of patient or organ during treatment

2. Organs at Risk: dose limiting normal tissue e.g. spinal cord

◘◘ After planning:

1. Treated Volume: enclosed by isodose line (equal or close to PTV)

2. Irradiated Volume: the volume receives 50% of the tumor dose (indicator of the quality of the plan)

The Target Volumes

Clinical target volume

Gross Tumor volume

Planning target volumeTreated volume

Irradiated volume

◘◘ Clinical Methods :• Clinical examination: inspection, palpation

• Surgical findings and metal clips at fixed points

◘◘ Radiological Methods:• Diagnostic x-ray unit:

- Comparison with simulator (distance, focus, magnification)?

• Simulator Unit:

• Conventional

• Computed Tomography (CT)

Localization of the Target Volumes

What is the Simulators?

Simulator

A diagnostic x-ray machine which:

accurately simulates the geometry, optical systems and mechanical movements of a radiotherapy machine.

Importance:

1. Localization: the target volume and critical normal tissue with respect to skin marks

2. Simulation: the planned treatment fields with respect to tumor and normal tissue

Simulator

ZX

Y

Simulator: Main components

• Gantry rotation around a horizontal axis

• Source axis distance (SAD) motion in radial direction

• Collimator rotation

• Image intensifier motion in the vertical, longitudinal and

radial directions

• Table movement ( rotation, vertical, longitudinal and

lateral)

• Movement of X-ray field collimators and the wires (ruler)

Simulator

Shielding Block Tray

Localization by conventional simulator

Conventional & CT Simulators

C.T. Simulator : Uses

1.Localization of tumor and normal tissues

2.Direct determination of body contour in different planes (2D, 3D)

3.Dose calculation in different tissues (pixel density)

C.T. Simulator : Specification

1.Wide gantry opening

2.Flat top table

3.Laser system

4.The couch movement

5.Rapid scanning

6.Slice thickness

7.Measurement of CT number

8.Making cuts in different planes

Conventional & CT Simulators

CT simulation

The CT scans are linked with a specialized treatment planning computer providing detailed information which

will assist with optimum treatment .

Localization by C.T Simulator