بسم الله الرحمن الرحيم ﴿و قل رب زدنى علماً﴾ صدق الله العظيم

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

Planning (1)

Patient Positioning & Immobilization

Patient Positioning: General Rules EBRT Planning Patient Positioning: General Rules 1. Comfortable position 2. Easily and accurately reproducible (day to day) 3. All fields should be treated in the same position 4. No obstruction in the beam pathway 5. The simulator couch: similar to that of treatment 6. Laser beam systems: increasing accuracy

Immobilization Methods EBRT Planning Immobilization Methods ◘ Simple methods: Head & neck rest Bite block ◘ Plaster of Paris cast: Limited volume: joint, limb, head &neck Whole body: wide field (e.g. medulloblastoma) ◘ Mask for head and neck: Plastic Thermoplastic ◘ Mattresses and cushions: Plastic sac (small polystyrene beads, vacuum pump) Different shapes and sizes

Supine Head Support

Construction of Head & Neck plastic mask-1 Positioning of patient ► ▲ Lifting off the negative ▲ Taking of impressions

Construction of Head & Neck plastic mask-2 ► Negative Mould ► Filling with plaster ► ► Positive Mould►

Construction of Head & Neck plastic mask-3 The positive on vacuum former

Construction of Head & Neck plastic mask-4 The positive with molded mask ► The mask ▼ ▲ The completed mask with treatment markings

Construction of Head & Neck plastic mask-5 Patient lying on linear accelerator machine couch with treatment plastic mask

Immobilization methods-1 ► Thermoplastic head & neck mask ► Thermoplastic face mask

Immobilization methods-2 Total body plaster cast ► ◄ Alpha Cradle used for body

Contouring

Contouring ◘ Definition: The outer circumference of the patient In the transverse plane in central axis of the field Indicate anatomical relationships: - Target volume and normal tissues - Fixed landmark or position of tattoos - Isodose curve (s) ◘ Importance: reference during daily treatment ◘ Methods: Lead solder Plaster of Paris strip Laser beam

► A cross section of the body and positioning of beams on the tumor ◄ A cross section of the body and the levels of radiation caused by the beam placement in the above image

Fields Arrangement

Fields Arrangement Central axes: same plane & meet at the isocentre Planning Fields Arrangement ► Single field: ► Two fields: Parallel opposing Non-parallel Tangential ► Three fields: Anterior + two lateral opposing Anterior + two posterior oblique ► Four fields: ► Rotation & arc: Central axes: same plane & meet at the isocentre

The Choice of Field Arrangement Planning The Choice of Field Arrangement Factor affecting: 1. Position of the target volume 2. Size of the target volume 3. Position of the structures to be avoided. 4. Beam energy available / required 5. Beam modality available / required 6. Technical feasibility of equipment 7. Patient positioning.

Fields Arrangements -1 Two parallel opposing fields ► e.g. palliative treatment ▲ Single field e.g. Skin cancer ◄ Two tangential fields, e.g. breast or chest wall irradiation

Fields Arrangements -2 ▲ ▲ Four fields Three fields e.g. Prostate cancer ▲ Three fields e.g. Bladder cancer

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