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Rth de haute technicité 1- La RCMI

S. Marcié Unité de Physique Centre Antoine-Lacassagne (CAL) Nice. Rth de haute technicité 1- La RCMI. Historique. Pourquoi cette technique ? Pourquoi maintenant ? Multilames (depuis 10 ans), Pilotage des accélérateurs, Puissance des systèmes de calcul. x2. x2. x2. x2. Méthodes.

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Rth de haute technicité 1- La RCMI

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  1. S. Marcié Unité de Physique Centre Antoine-Lacassagne (CAL) Nice Rth de haute technicité1- La RCMI Physique/CAL 2012-2013

  2. Physique/CAL 2012-2013 Historique Pourquoi cette technique ? Pourquoi maintenant ? Multilames (depuis 10 ans), Pilotage des accélérateurs, Puissance des systèmes de calcul

  3. Physique/CAL 2012-2013

  4. Physique/CAL 2012-2013

  5. x2 x2 x2 x2

  6. Physique/CAL 2012-2013 Méthodes Statique dite « step and shoot » Dynamique dite « sliding windows » ou dynamique Arcthérapie modulée

  7. Physique/CAL 2012-2013 Matériels Accélérateur avec collimateur multilames, Système de calcul avec logiciel inverse, Moyens de contrôle de qualité

  8. Physique/CAL 2012-2013

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  10. Physique/CAL 2012-2013 Le collimateur multilames du Primus

  11. Physique/CAL 2012-2013 Several MLC

  12. Physique/CAL 2012-2013 Several MLC MLC jaw Y jaw Y jaw X Y backup MLC MLC jaw X ELEKTA replacement Of the upper jaw VARIAN additionnal collimator SIEMENS replacement of the inferior jaw - Arc movement- C.Mubata, SFPH Tours 99)

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  22. Contrôles de qualité Les collimateurs multilames Physique/CAL 2012-2013

  23. Physique/CAL 2012-2013 MLC and IMRT: "overtravel" Profiles (Step-Shoot) 4 segments and 3 levels axis Intensity levels 4 Leaves displacement right left 3 2 1

  24. Physique/CAL 2012-2013 MLC and IMRT: "overtravel" Complex profiles => "overtravel" about 1/2 width of the max field Dynamic mode

  25. Physique/CAL 2012-2013 MLC and IMRT: leaves width Study of the homogeneity and the % dose in OAR in IMRT (Shepard et al., Med.phys 26 1212-1221) e => better homogeneity in the target, dose reduction in OAR

  26. Physique/CAL 2012-2013 MLC and IMRT: leakage / transmission In Step and Shoot, segments number: In SS, MU number x 3 / 3DCRT => leakage and transmission x 3 => Transmission /leakage MLC < 2% (IEC 601-2-1, 1998) UM If transmission MLC of 1%: Ttotale = 9 seg x10 MU x1% = 0.9 UM = 1,8% total dose 50 8 9 40 6 7 30 4 5 20 2 3 10 1

  27. Physique/CAL 2012-2013 MLC and IMRT: leakage / transmission In SW, during irradiation, each field point has more time under the MLC : about 4 to 6% of the total dose totale is due to the transmission => better modelisation by the TPS

  28. Physique/CAL 2012-2013 MLC and IMRT: geometry (1) The segmentation algorithm suppose the independance of adjacent leaves => the MLC must atminimum be focused in the direction of adjacent leaves Idealy, the MLC is also focused in the direction of opposite leaves MLC double focused

  29. Physique/CAL 2012-2013 MLC and IMRT: geometry (2) non focused leaves and rounds (cste penombra): - Variation of the transmission along the leaf (=> offset of 1 mm) - Correspondance light/irradied field ? => corrections (files/offset) Offset de 1mm LoSasso et al., Med. Phys. (25) 1998

  30. Physique/CAL 2012-2013 Effet « tongue and groove » ou tenon-mortaise

  31. Physique/CAL 2012-2013 MLC and IMRT: geometry (3) Shape "tongue-and-groove" of adjacent leaves ( to limite leakages) gives an under-dosage at the junction => the segmentation can avoid this effect 1st segment 2nd segment tongue groove Under-dosage 50%

  32. Physique/CAL 2012-2013 MLC and IMRT: accuracy of leaves Static mode: Superposition of segments => lines of junction on the edges of segments Accuracy of the positioning => affects the dose distribution on the field edges Variation of "Output Factor" OF for small fields => influence on the dose/ small segment

  33. Physique/CAL 2012-2013 MLC : accuracy of leaves (SS) => Step-and-shoot: MLC accuracy < 2 mm (field > 1cm) B. Rhein, DKFZ, Heidelberg

  34. Physique/CAL 2012-2013 Multileaf collimator

  35. Physique/CAL 2012-2013 MLC and IMRT: accuracy of leaves Dynamic mode: Positioning errors of leaves => errors on the dose over the field Prescribed position Real position Real dose different From prescribed dose gap

  36. Physique/CAL 2012-2013 MLC and IMRT: leaves position Tolerance on the leaf position gap => dynamic: accuracy MLC < 0.2 mm LoSasso et al., Med. Phys. (25) 1998

  37. Physique/CAL 2012-2013 "classics" tests in 3DCRT: Perpendicularity of leaves Rotation axis of MLC, of gantry Penumbra Gravity effect ... MLC: quality control

  38. Physique/CAL 2012-2013 Ratio dose under the MLC closed, dose for a 10x10 cm² field at the reference depth (film, chamber) Leakage and transmission 2.0 On Primus 10 cm 1.5 1.0 0.5 - tolerance: 2% - Once a year

  39. Physique/CAL 2012-2013 900 800 Dose for 1200 UM 700 600 500 Profile axis 400 300 Ideal profile 200 100 Measured profile 0 -50 -40 -30 -20 -10 0 10 20 30 40 50 in plane (mm) Influence on dose profile of misalignment of some leaf

  40. Physique/CAL 2012-2013 Example of DKFZ, Siemens - tolerance +/- 1mm in SS - once a month Leaves calibration (SS) On Primus Dose 100% 50% Distance (mm) 3 x 40 cm²

  41. Physique/CAL 2012-2013 Real/prescribed position (SS) Superposition of 2 x1/2 fields (junction line) - tolerance +/- 1mm in SS - twice a week On Primus Prescribed position

  42. Physique/CAL 2012-2013 5 fields of 0,4 x 40 cm² at different axis distances - The leaves must be aligned - The 5 lines must have the same width - Twice a week Accuracy of leaves position (SS) On Primus 0.4 x 40 cm²

  43. Physique/CAL 2012-2013 "Continous stripe test": To verify the leaves position, the speed, the acceleration /deceleration - - if v=cste => uniform dose - twice a week Quality control of the MLC (SW) Volontaries errors - 0.5 mm - 0.2 mm Lame gauche UM 1 mm Lame droite + 0.2 mm + 0.5 mm position LoSasso et al., Med. Phys. (25) 1998

  44. Physique/CAL 2012-2013 Speed stability The adjacent leaves move at different speeds but cste => bands of different but uniform intensities - uniform dose profiles if speed is stable Quality control of MLC (SW) MU Left leaf N°3 Right leaf N°1 N°2 N°2 N°1 N°3 position LoSasso et al., Med. Phys. (23) 1996

  45. Physique/CAL 2012-2013 Sliding window: To verify the gravity effect + position + speed + acceleration For 4 angles of the gantry, a field of 0,5 x 25 cm² move uniformly - the dose and the dose profiles must be uniform for the 4 positions Quality control of MLC (SW) Acceleration effect Stop of leaves can be previous (effect of the acceleration and deceleration) LoSasso et al., Med. Phys. (25) 1998

  46. Autres points Physique/CAL 2012-2013

  47. Physique/CAL 2012-2013 Small number of MU - Small number of MU : flatness, symetry, dose = f(MU) On Primus

  48. Dosimetry of Small Monitor Unit Segments in IMRT Delivery • Deviation from Mean Dose for 30 Fraction Segment for 1 MU. • Deviation from Mean Dose for 20 Fraction Segment for 2 MU. • Deviation approaches < 0.5% for higher (>5) MU Physique/CAL 2012-2013 Courtesy by Fox Chase Cancer Center, Philadelphia

  49. Verification of homogeneity and symmetry of LOW MU Results for 1-10 MU • Beam Flatness (PRIMUS): • 1.48-1.78% (in-plane) • 1.45-1.7% (cross-plane) • Symmetry: • 0.24-1.26% (in-plane) • 0.53-1.08% (cross-plane) Physique/CAL 2012-2013 Courtesy by Fox Chase Cancer Center, Philadelphia

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