Hugues Mailleux Medical Physics Department Institut Paoli-Calmettes - - PowerPoint PPT Presentation

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Hugues Mailleux Medical Physics Department Institut Paoli-Calmettes - - PowerPoint PPT Presentation

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Hugues Mailleux Medical Physics Department Institut Paoli-Calmettes Marseille France Sunday 17 July 2016 AGENDA 1. Introduction 2. Material 3. Optimization process 4. Results 5. Comments 6. Conclusion 7. Thanks INTRODUCTION o

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Hugues Mailleux Medical Physics Department Institut Paoli-Calmettes Marseille France Sunday 17 July 2016

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AGENDA

1. Introduction 2. Material 3. Optimization process 4. Results 5. Comments 6. Conclusion 7. Thanks

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INTRODUCTION

  • Plan Competition: opportunity to evaluate our current

treatment technique for left sided breast  VMAT with 2 partial arcs  First patient treated in september 2014

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TREATMENT PLANNING SYSTEM

  • RayStation (RaySearch) r.5.0

 Dose calculation for photon beams

  • Collapsed cone convolution superposition algorithm
  • GPU: Fluence + Convolution

 Plan Optimization

  • Standard inverse planning
  • Clinical goals
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TREATMENT PLANNING SYSTEM

  • Clinical goals
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ACCELERATOR

  • Versa HD (Elekta)

 Standard 6 MV  MLC Agility

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OPTIMIZATION PROCESS

  • 1. Beam geometry
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ISOCENTER POSITION

  • Not guided by dosimetric considerations but by technical

constraints:

  • Constraint n°1: CBCT

 The isocenter must be placed to avoid collisions

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SLIDE 9

ISOCENTER POSITION

  • Constraint n°2: CBCT

 The isocenter must be placed to get the entire breast inside the field of view

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ISOCENTER POSITION

  • Constraint n°3: Jaws and MLC maximum opening

 The isocenter must be placed to cover the entire PTV

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BEAM GEOMETRY

  • No couch rotation
  • Gantry

 Arc 1: 170° → ~ 300°  Arc 2: ~ 300° → 170°

  • Collimator :

 Arc 1: 5°  Arc 2: 355°

  • Grid size:

 Plan Competition: 1,5 mm  Current practice: 3 mm

  • Gantry spacing between 2 CP: 4°
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OPTIMIZATION PROCESS

  • 2. Create additional

structures

  • 1. Beam geometry
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ADDITIONAL OPTIMIZATION STRUCTURES

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ADDITIONAL OPTIMIZATION STRUCTURES

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ADDITIONAL OPTIMIZATION STRUCTURES

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OPTIMIZATION PROCESS

  • 3. Initial objectives
  • 2. Create additional

structures

  • 1. Beam geometry
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SLIDE 17

OPTIMIZATION PROCESS

  • Initial objectives
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SLIDE 18

OPTIMIZATION PROCESS

  • Initial objectives
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SLIDE 19

OPTIMIZATION PROCESS

  • 3. Initial objectives

PTV criteria OK ?

  • 2. Create additional

structures

  • 1. Beam geometry
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INITIAL OBJECTIVES

  • Uniform dose and prescription

 Usually: 50 Gy to median dose (ICRU 84)  in this case: 51,5 Gy to median dose

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INITIAL OBJECTIVES

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OPTIMIZATION PROCESS

  • 3. Initial objectives
  • 4. Add OAR objectives

(weight = 1) PTV criteria OK ?

  • 2. Create additional

structures

  • 1. Beam geometry
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OAR CRITERIA

  • 2 types of criteria for OAR:

 maximum dose

  • Rigth breast
  • Spinal cord

 Parallel organs

  • Heart
  • Left lung
  • Rigth lung
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SLIDE 24

MAXIMUM DOSE CRITERIA

  • Maximum dose:
  • Rigth breast
  • Spinal cord
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MAXIMUM DOSE : OAR OBJECTIVES

  • Additonal structures

 Breast rigth + 2 mm  Spinal cord + 2 mm

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PARALLEL OAR CRITERIA

  • Parallel OAR
  • Heart
  • Left Lung
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SLIDE 27

PARALLEL OAR CRITERIA

  • Parallel type OAR dosimetric criteria
  • Rigth Lung:
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PARALLEL OAR OBJECTIVES

  • Only one objectif by OAR
  • Initial weight: 1
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OPTIMIZATION PROCESS

  • 3. Initial objectives

(PTV, ring)

  • 4. Add OAR objectives

(weight = 1)

  • 5. Fine-tune parallel

OAR objectives clinical goals OK ? End

  • 6. increase the weight
  • f the OAR objectives
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HOW TO PUT THE MAXIMUM DOSE INSIDE DE CTV-LUMPECTOMY

  • Additional structure:

 PTV – (CTV-LUMPECTOMY)  Add objectives:

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RESULTS

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RESULTS

Better !

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DELIVERY TIME

  • Delivery time:

 Arc 1: 1’13”  Arc 2: 1’18”

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PATIENT-SPECIFIC QA

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PATIENT-SPECIFIC QA

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COMMENTS: INTERFRACTION MOVEMENT

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COMMENTS: INTERFRACTION MOVEMENT

  • How to take this into account ?

 For fixed fields: skin flash  VMAT ?

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COMMENTS: INTERFRACTION MOVEMENT

  • Virtual bolus
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COMMENTS: INTERFRACTION MOVEMENT

  • Optimization: 2 step process

1) With virtual bolus: Optimization on the PTV OUTSIDE 2) After having removed the virtual bolus: Optimization

  • n the PTV without

modifying the shape of the segments

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COMMENTS: INTERFRACTION MOVEMENT

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COMMENTS

  • In our current technique, we use additional objectives for:

 Larynx  Thyroid  esophagus

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CONCLUSION

  • Some (humble) recommendations:

 Well-defined methodology

  • learning curve
  • homogeneity of practices

 As simple as possible:

  • 2 arcs
  • No couch rotation
  • As few objectives as possible for optimization

 Use of Virtual bolus

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THANKS

 Ahmad Nobah  Radiation Oncologists  Medical Physics team  RaySearch  My Family