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بسم الله الرحمن الرحيم

بسم الله الرحمن الرحيم. ﴿ و قل رب زدنى علماً ﴾. صدق الله العظيم. Introduction to Radiotherapy. RAD 461. Dr. Ahmed Al Far, M.D. Professor of Radiation Oncology. Planning (3). Radiation Beam Modifiers. Introduction. Isodose curves: prepared under Standard Conditions.

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بسم الله الرحمن الرحيم

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

  2. Introduction to Radiotherapy RAD 461 Dr. Ahmed Al Far, M.D. Professor of Radiation Oncology

  3. Planning (3)

  4. Radiation Beam Modifiers

  5. Introduction Isodose curves: prepared under Standard Conditions • The homogeneity of the medium (water) • The vertical incidence of the beam axis on surface • The flatness of the irradiated surface • No obstructing part of the radiation field Are conditions in clinical practice always standard ? • Radiation Beam Modifiers • Beam shaping devices • Tissue compensators • Wedge filters

  6. Beam Shaping Shielding Blocks Uses:protect some parts laying within the field ? Thickness:5 HVL can absorb 95% of radiation Made of:lead or Cerrobend (lead + bismuth) Place:over a tray mounted in the treatment head Sides:have same degree of beam divergence Distance:minimum 15 cm from skin A standard set: is supplied with treatment machine How canyou construct a Cerrobend block?

  7. Shielding Block Thickness depends on: 1. Shielding material 2.Radiation energy

  8. Tissue Compensators Uses: correct for irregular or curved surface (A) For Kilovoltage Radiation • Placement: directly on the skin surface (B) For Megavoltage Radiation • Placement: at distance from patient’s skin

  9. In case of MVradiation Compensate for irregular surface A’E’C’) I) D’ B’ A’ I C’ E’ In case of KV radiation Compensate for irregular surface AEC (II) D B A II C E

  10. Wedge Filters Uses:correct for inhomogeneous dose distribution by tilting parallel isodose line in the direction of the thin end of the filter. Made of:lead Place:over a tray mounted in the treatment head Distance:minimum 15 cm from skin Wedge angle:between 50% isodose line and a line at right angle to the central axis • Wedge Systems: • Individualized: a separate wedge for each field, telecobalt ? • Universal: a single wedge for all field sizes, L. accelerator ?

  11. Wedge Filters Used in superficial tumors: e.g. parotid or maxillary sinus

  12. The Hinge Angle  A B Dose at point A is greater than that at point B ? Wedge angle = 90o – ( / 2)

  13. Thank You

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