Isodose CurvesAdhikari Abish, MD Resident     NAMS/BPKMCH                        2013.01.11, Bharatpur                    ...
DefinitionIsodose curves are the lines joiningthe points of equal PercentageDepth Dose (PDD), therefore ameans of mapping ...
DefinitionIsodose curves are the lines joiningthe points of equal PercentageDepth Dose (PDD), therefore ameans of mapping ...
Depends upon•   Beam energy (quality)•   Field size•   SSD•   Attenuating factors•   Source geometry/collimation          ...
10 x 10 cm field. Cobalt-60   5
Measurement of Isodose Curves                                                              A                              ...
Isodose Curve Depends on Beam Quality     200 kVp, bulging                       Co-60, penumbra    penumbra due to       ...
Isodose Curve Depends upon the Field SizeField size is determined based on dosimetric coverage, notgeometric coverage.    ...
Isodose Curve Effected by Wedge Filter                                                        Normalized to dmax without w...
Wedge Field Techniques                  180            160      140                                   90                  ...
Wedge Field Techniques (hinge angle and wedge angle)        hinge angle                                                   ...
Isodose Distribution – parallel opposed fields
13
THANK YOU            15
Isodose curves
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Isodose curves

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Isodose curves

  1. 1. Isodose CurvesAdhikari Abish, MD Resident NAMS/BPKMCH 2013.01.11, Bharatpur 1
  2. 2. DefinitionIsodose curves are the lines joiningthe points of equal PercentageDepth Dose (PDD), therefore ameans of mapping variation in thedose as a function of depth andtransverse distance from the centralaxis of the beam. 2
  3. 3. DefinitionIsodose curves are the lines joiningthe points of equal PercentageDepth Dose (PDD), therefore ameans of mapping variation in thedose as a function of depth andtransverse distance from the centralaxis of the beam. 3
  4. 4. Depends upon• Beam energy (quality)• Field size• SSD• Attenuating factors• Source geometry/collimation 4
  5. 5. 10 x 10 cm field. Cobalt-60 5
  6. 6. Measurement of Isodose Curves A B Homogenous PhantomDose measurement in a water phantom: Flat SurfaceA. Moving probe (central axis depth dose, beam profile) Perpendicular beamB. Fixed reference probe (position fixed, located in field)C. Relative dose = A/B IBA - Wellhofer Blue Phantom 6
  7. 7. Isodose Curve Depends on Beam Quality 200 kVp, bulging Co-60, penumbra penumbra due to primarily due to sourcegreater scatter of low size (geometric energy photons. penumbra)4 MV, small penumbra, 10 MV, penumbra due to small photon greater than that of 4 scatter and short MV, due to greater electron range electron range 7
  8. 8. Isodose Curve Depends upon the Field SizeField size is determined based on dosimetric coverage, notgeometric coverage. 8
  9. 9. Isodose Curve Effected by Wedge Filter Normalized to dmax without wedge Normalized to dmax with wedge (open field)d = 10 cm wedge wedge angle angle Wedge Angle : ICRU #24: The angle through which an isodose curve is titled at the central ray of a beam at a specified depth. (10 cm) 9
  10. 10. Wedge Field Techniques 180 160 140 90 90 80 70 Uniform120 80 dose 60 70 50 60 Orthogonal pair – open field Orthogonal pair – wedged field 10
  11. 11. Wedge Field Techniques (hinge angle and wedge angle) hinge angle θ wedge angle  90 2 φIn clinical reality, this relationship isn’ttrue in general, due to surfacecurvature.Computer treatment plan is needed tofind the optimal wedge angle 11
  12. 12. Isodose Distribution – parallel opposed fields
  13. 13. 13
  14. 14. THANK YOU 15
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