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Random and systematic errors 25.10.12
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  • Gli errori random non hanno effetti consistenti sull’intero campione.Se osserviamo tutti gli errori random in una distribuzione, la loro somma dovrebbe essere zero. L’importante proprietà degli errori random è che aggiungono varibilità ai dati ma non variano la media della performace del gruppo.
    Systematic errors tend to be consistently either positive or negative, because of this, systematic errors is sometimes considered to be bias in measurements.
  • Gli errori random non hanno effetti consistenti sull’intero campione.Se osserviamo tutti gli errori random in una distribuzione, la loro somma dovrebbe essere zero. L’importante proprietà degli errori random è che aggiungono varibilità ai dati ma non variano la media della performace del gruppo.
    Systematic errors tend to be consistently either positive or negative, because of this, systematic errors is sometimes considered to be bias in measurements.
  • When considering geometric uncertainties in radiotherapy, the term systematic error may be used when referring to the individual patient, or to the treatment population, and this distinction needs to be clarified to avoid confusion.
    Systematic errors may be introduced into a patient’s tratment at the localisation, planing or treatment delivery phases. For this reason these types of errors are often referred to as treatment preparation errors. Once frozen into the process, systematic errors will occur in each tratment fraction. Possible tratment preparation errors are summarised below.
  • Artefatti di movimento.
    Pensiamo infatti il caso la vel di scansione TC è inferiore alla velocità del movimento degli organi: l’immagine verrà sfumata
    Se è MENO rapido il movimento del target fotograferò l’immagine in una fase arbitraria.
    Ma quand’anche fossero simili cmq la posizione potrebbe essere distorta.
    La soluzione potrebbe essere nella TC 4D, nella quale non entriamo nel merito essendo argomento delgi altri incontri.
  • E questo è quello che potrebbe accadere a degli oggetti…
    questo ci fa comprendere come la contornazione potrebbe risentire della distorsione del target dovuta a questi artefatti.
  • .
  • .
  • .
  • Solo per chiarire meglio tra di noi.
    Sarebbe più semplice se tutti prendessimo la nostra mano e provassimo a simulare tali shift.
    Il pitch, a volte nominato anche tilt, corrisponde a quella che volgarmente potremmo ricondurre alla inclinazione del lettino. E’ una rotazione che avviene intorno all’asse laterale e che può essere visualizzata nelle immagini saggittali..viene più semplice pensare allo spostamento all’interno della maschera di un paziente testa collo ad es.
    Per Roll si intende invece una rotazione intorno all’asso longitudinale, visualizzabile nelle immagini assiali.
    Mentre per yaw o rotation si intende la rotazione intormo all’asse verticale che possiamo correggere matchando le immagini coronali.
    Se gli shif traslazionali li misuriamo in cm, quelli rotazionali in gradi.
  • Relativamente alle precedenti due settimane, vorremo presentarvi dei dati geometrici preliminari relativamente allo studio di 5 pazienti prostata trattati con tecnica rapidarc. Sono state effettuate 40 CBCT e da ognuna di queste ottenute una sestina di shift: x,y,z,pitch, roll e yaw. Ribadisco che sono dati estremamenti preliminari, viziati probabilmente da errori sistematici dovuti da una fase ancora di apprendimento nell’utilizzo della macchina.
  • I cinque grafici piccoli si riferiscono ai 5 pazienti. Sull’asse orizzontale è riportato il numero della frazione, su quello verticale la variazione della traslazione (in cm) e quella della rotazione (in gradi). In evidenza il grafico di Perone in cui si nota un elevata variazione del pitch, probabilmente per l’utilizzo del belly board
  • I cinque grafici piccoli si riferiscono ai 5 pazienti. Sull’asse orizzontale è riportato il numero della frazione, su quello verticale la variazione della traslazione (in cm) e quella della rotazione (in gradi). In evidenza il grafico di Perone in cui si nota un elevata variazione del pitch, probabilmente per l’utilizzo del belly board
  • La slide evidenziata invece vuole sottolineare che in tal caso è il roll lo shift dominante: visto però che oscilla lontano dallo zero, al contrario degli altri shift, probabilmente potrebbe essere quindi ad un errore sistematico di set-up
  • La slide evidenziata invece vuole sottolineare che in tal caso è il roll lo shift dominante: visto però che oscilla lontano dallo zero, al contrario degli altri shift, probabilmente potrebbe essere quindi ad un errore sistematico di set-up
  • In questa slide si evidenza come al’aumentare del numero delle frazione le oscillazioni dei valori degli shift tendano al valore dell’asse verticale pari a zero. Questo potrebbe essere interpretato come una migliore compliance del paziente dopo un’iniziale incertezza provocata dalla terapia.
  • In questa slide si evidenza come al’aumentare del numero delle frazione le oscillazioni dei valori degli shift tendano al valore dell’asse verticale pari a zero. Questo potrebbe essere interpretato come una migliore compliance del paziente dopo un’iniziale incertezza provocata dalla terapia.
  • E' la revisione della completezza ed accuratezza del lavoro svolto eseguita da una persona con idonee competenze che non è stata coinvolta nell'esecuzione dello stesso e della quale lascia un riscontro firmato. Obiettivo dell'indi è monitorare il corretto svolgimento del processo.
    IC1) un medico in formazione e med resp sett o med strutturato verificano la documentAZIONE relativa all’impostaz del tratt radiante per verificare se la prescrizione è stata applicata secondo le indicazioni del MDQ
    IC2) un medico in formazione e med resp sett o med strutturato rivedono la cartella, verificano la documentAZIONE relativa all’impostaz del tratt radiante e verificano se i dati relativi alle geometrie di irradiazione sono stati riportati sulla CT secondo le indicazioni del MDQ

Transcript

  • 1. XXIII Corso Residenziale di Aggiornamento Moderna Radioterapia e Diagnostica per Immagini: dalla definizione dei volumi alla radioterapia «adaptive» Il Glossario per il corso: Random and systematic errors M. Balducci, L. Azario, A. Fidanzio, S. Chiesa, B. Fionda, L. Placidi, G. Nicolini
  • 2. Random and systematic errors Courtesy of Tufve Nyholm, In Room Imaging and RM planning ESTRO Course 2012
  • 3. RT Definition: - Systematic error Σ is a deviation that occurs in the same direction and is of a similar magnitude for each fraction throughout the treatment course - Random error σ is a deviation that can vary in direction and magnitude during the treatment “On target: ensuring geometric accuracy in radiotherapy", Theo Royal College of Radiologist, Institute of Physics and Engineering in Medicine, Society and College of Radiographers
  • 4. Σ and σ Σ Σ systematic errors -> mean value σ σ random error -> standard deviation
  • 5. Σ and σ Standard deviation: Average value Standard Deviation
  • 6. How estimate Σ vs σ errors? Lets say shift to right + and shift to left <x> SD Example A (mm) +5 +4 +3 +2 +1 0 -1 -2 -3 -4 -5 0 3.3 Example B (mm) +10 +8 +6 +4 +2 0 -2 -4 -6 -8 -10 0 6.6 Example C (mm) +9 +8 +7 +6 +5 +4 +3 +2 +1 0 -1 3.3 σ 4 Σ
  • 7. Individual and population error Σ • individual Σi : σ • individual σi: for an individual patient is the mean error over the course of treatment for an individual patient is the SD of the measured errors over the course of treatment • population Σp: • population σp: for a group of patients is the SD of Σi for a group of patient is the mean of σi “On target: ensuring geometric accuracy in radiotherapy", Theo Royal College of Radiologist, Institute of Physics and Engineering in Medicine, Society and College of Radiographers
  • 8. Effect of errors on dose Random errors blur the cumulative dose distribution CTV Systematic errors shift the cumulative dose distribution CTV
  • 9. Blurred dose Blur planned dose distribution with all errors to estimate the cumulative dose distribution
  • 10. PTV margin
  • 11. What should be the margin?
  • 12. PTV margin recipe for dose - probability 90% of the patients must get a minimum CTV isodose of 95%: PTV margin = 2.5 Σp + 0.7 σp 1) Add first margin so that 90% of the systematic errors are covered: 2.5 Σp 2) Add margin random variation so that CTV+ first margin lies within the 95% isodose: 0.7 σp Van Herk et al, IJROBP 47: 1121-1135, 2000
  • 13. Random and systematic errors Courtesy of Tufve Nyholm, 2012
  • 14. Random and systematic errors
  • 15. Random and systematic errors PHASE Error Correction
  • 16. Registration/Simulation:  It allows the construction of a “geometrical model” of patient’s set-up (Reference home position)  Errors in this phase influence each treatment fraction. Systematic error
  • 17. Registration/Simulation: correction? Prevent!!! Choose!!! Head & Neck Breast Lung / Liver Pelvic
  • 18. Registration/Simulation: correction? Prevent!!! Choose!!! UNIFRAME PMMA Variability mean dose to PTV Out of 10 pts UNIFRAME CARBONIO Variability mean dose to PTV Max UNIFRAME PMMA 2.90% 6.50% UNIFRAME CARBONIO 1.10% 2.80%
  • 19. Registration/Simulation: correction? Prevent!!! Positioning: comfortable
  • 20. Random and systematic errors PHASE Error Correction SYSTEMATIC • CHOOSE of Immobilization devices • Comfort
  • 21. Target definition/Contouring Wrong delineation of normal tissue Wrong definition of the target target
  • 22. Target definition/Contouring PAST Traditional Simulation PRESENT Virtual Simulation TC per: • contouring target and ORA • creat irradiated volum corresponding to CTV
  • 23. Target definition/Contouring CAMPOBASSO ALTERATION OF MOVEMENTS Vel CT scan <<< Vel Target Motion Target “smeared” image Vel CT scan >>> Vel Target Motion Image «frozen» in a random phase Vel CT scan ± Vel Taget motion Distortion of Image and position
  • 24. Target definition/Contouring CAMPOBASSO Alteration of movements Photo Static state Dynamic State Jiang SB, Semin Radiat Oncol 2006 Oct; 16(4):239-48.
  • 25. Target definition/Contouring Wrong delineation of normal tissue Wrong definition of the target target Inter-observer Intra-observer
  • 26. OBJECTIVES 1.To quantify multiobserver variability of target and organ at risk delineation for breast cancer radiotherapy MATERIALS & METHODS •Lumpectomy cavity •Boost PTV •Breast •Heart •Internal mammary N •Axillary N •Supraclavical N 1)Volume 2) Distance center mass 3) Percent overlap 4) Average surface distance
  • 27. OBJECTIVES 1.To quantify interclinician variability in contouring common OARs of the head/neck and 2. To quantify the change in dosimetric metrics of an IMRT plan due strictly to the OAR differences. MATERIALS & METHODS Brainstem Brain Left parotid Mandible Righ parotid Spinal cord 1)Mean Volum+SD 2) DICE coefficient 3) Volumetric algorithm
  • 28. Target definition/Contouring Wrong delineation of normal tissue Wrong definition of the target target Inter-observer Systematic Error Intra-observer
  • 29. Target definition/Contouring: correction Optimization!!!  Image quality: Theragnostic CT simulation RM/PET-CT
  • 30. 11 observers from 5 institutions, 22 patients
  • 31. 11 observers from 5 institutions, 22 patients
  • 32. 11 observers from 5 institutions, 22 patients Conclusion: For high-precision radiotherapy, the delineation of lung target volumes Conclusion: For high-precision radiotherapy, the delineation of lung target volumes using only CT introduces too great a variability among radiation oncologists. using only CT introduces too great a variability among radiation oncologists. Implementing matched CT–FDG-PET and adapted delineation protocol and Implementing matched CT–FDG-PET and adapted delineation protocol and software reduced observer variation in lung cancer delineation significantly with software reduced observer variation in lung cancer delineation significantly with respect to CT only. However, the remaining observer variation was still large respect to CT only. However, the remaining observer variation was still large compared with other geometric uncertainties (setup variation and organ motion). compared with other geometric uncertainties (setup variation and organ motion).
  • 33. Target definition/Contouring: correction Optimization!!!  Image quality: Theragnostic CT simulation RM/PET-CT Contouring Atlas - navigator - expert opinion - Consensus panel - Tutorial Co-registration software Indipendent Check
  • 34. Target definition/Contouring: correction Appropriate Margins Standard? Formula Van Herk? PTV margin = 2.5 Σ + 0.7 σ
  • 35. Random and systematic errors PHASE ERROR SYSTEMATIC SYSTEMATIC CORRECTION • CHOOSE of Immobilization devices • Comfortable Theragnostic Image quality Contouring Atlas Co-registration software Indipendent Check
  • 36. Conclusions: Differences in target and OAR delineation for breast irradiation between institutions/observers appear to be clinically and dosimetrically significant. A systematic consensus is highly desirable, particularly in the era of intensitymodulated and image-guided RT.
  • 37. Conclusion: The effects of interclinician variation in contouring organs-at-risk in the head and neck can be large and are organ-specific. Physicians need to be aware of the effect that variation in OAR contouring can play on the final treatment plan and not restrict their focus only to the target volumes.
  • 38. Treatment design/ Planning
  • 39. Random and systematic errors PHASE ERROR SYSTEMATIC CORRECTION • CHOOSE of Immobilization devices • Comfortable SYSTEMATIC Theragnostic Image quality Contouring Atlas Co-registration software Indipendent Check SYSTEMATIC Indipendent Check
  • 40. Random and systematic errors PHASE ERROR SYSTEMATIC CORRECTION • CHOOSE of Immobilization devices • Comfortable SYSTEMATIC Theragnostic Image quality Contouring Atlas Co-registration software Indipendent Check SYSTEMATIC Indipendent Check
  • 41. Random and systematic errors
  • 42. Radiotherapy treatment process Correct position of the patient (SPACE) every day of the n-days of treament (TIME) … 46
  • 43. Inter-fractional versus Intra-fractional  Inter-fractional – Variation between fractions 47  Intra-fractional – Variation within a fraction
  • 44. Sources of error Organ motion • • • • • • Breathing Peristalsis Swallowing Bladder filling Rectum filling Etc. Intrafraction Random Interfraction 48 Kutcher G, Seminars in Radiation Oncology, 1995: 5 (2): 134-145
  • 45. Sources of error Target deformation • Weight loss (H&N) • Weight gain (swelling, systemic oedema) • Tumor shrinkage Interfraction • Tumor growth Systemati c 49 Kutcher G, Seminars in Radiation Oncology, 1995: 5 (2): 134-145
  • 46. Sources of error Patient setup • Anxiety • Breathlessness • Neurological deficit • Nausea • Pain • Discomfort • Etc. Random Random/Systema tic 50 Kutcher G, Seminars in Radiation Oncology, 1995: 5 (2): 134-145
  • 47. Error management Organ Motion/Target Deformation Midcourse replanning Setup protocols Gating Set-up Portal image verification 51 Online vs Offline
  • 48. Off-line correction Correction after treatment RT RT RT RT time
  • 49. On-line correction RT RT RT RT time Correction before treatment
  • 50. Offline/Online  Efficient correction of systematic …errors but not random  Minimum workload  Optimal number of controls: 10% of total fractions  Efficient control of systematic and random  Potentially time consuming  Possible increase in dose delivered Middleton M The Radiographer 2006: 53 (1): 24–28
  • 51. Online and Offline; Prospective and Retrospective Only studies with a separation between random and systematic errors Errors presented in three directions to disclose any directional dependence of set-up errors
  • 52. Head and Neck Differences in Casts use Coen W. Radiotherapy and Oncology 2001: 105-120
  • 53. Pelvic region Difference in immobilization Devices used Use of skin marks (respiration, weight change) Coen W. Radiotherapy and Oncology 2001: 105-120
  • 54. 6 Degrees of freedom (DOF)
  • 55. 24 pz 209 CBCT & 148 EPID < 2mm > 2° 3,7% prostata 26,4% torace 12,4% Head & Neck
  • 56. 24 pz 209 CBCT & 148 EPID < 2mm > 2° 3,7% prostata 26,4% torace 12,4% Head & Neck
  • 57. 24 pz 209 CBCT & 148 EPID Maximal 5° prostata 8° torace 6° Head & Neck < 2mm > 2° 3,7% prostata 26,4% torace 12,4% Head & Neck
  • 58. 24 pz 209 CBCT & 148 EPID No correlation between the magnitude of translational and rotational setup errors was observed < 2mm
  • 59. rotura: Preliminar geometrical data  From 27/09/2012 al 09/10/2012  5 prostate patients RapidArc  40 CBCT & 40 series of shifts (x,y,z,Pitch, Roll, Rtn)
  • 60. Geometrical Data/patients
  • 61. Geometrical Data/patients Pitch! Random error (wide Immobilization device? DS)
  • 62. Geometrical Data/patients
  • 63. Geometrical Data/patients Roll! Systematic error Set up?
  • 64. Geometrical Data/patients
  • 65. Geometrical Data/patients Incremento compliance paziente?
  • 66. Set-up errors SYSTEMATIC RANDOM
  • 67. Set-up errors Sources of errors 1) Mechanic errors (laser) 2) Patient’s errors 3) Immobilization devices 4) Technicians experience
  • 68. Set-up errors SYSTEMATIC GROUPS of patients Mechanic errors (laser) PATIENT
  • 69. Quality Controls
  • 70. Quality Controls: «morning Checkout»
  • 71. Quality Controls
  • 72. Quality Controls
  • 73. Quality Controls SYSTEMATIC GROUPS of patients PATIENT
  • 74. Set-up errors
  • 75. Set-up errors RANDOM PATIENT
  • 76. Quality Assurance Quality Indicator Indipendent check: Structure Process Results It 's the review of the completeness and accuracy of the procedures performed by a person with appropriate expertise who was not involved in the execution of the same procedure and which leaves a signature. The goal of the independet check is to verify the correct management of the process. IC 1 Planning IC 2 Delivery
  • 77. IVD TECHNIQUES • TLD (Thermoluminescent dosimeter) • Diodes • MOSFETs (Metal oxide semiconductor ) • OSL (Optically Simulated Luminescence) Single Point Dose Field Fluence Map • Gafchromic Film Dosimetry • Transmission EPID (Electronic Portal Imaging Device) Dosimetry • EPID Dosimetry + CBCT for 3D dose reconstruction 3D Volume Dosimetric Evaluation
  • 78. Errors detected by diode dosimetry: patient’s set-up variations ; incorrect TPS field implementation ( filters ); linac out-put factor variations; incorrect laser calibration. Errors detected by transit dosimetry: patient’s set-up variations ; patient’s morphological changes (due to gas pockets or tumor regression in the lung) ; attenuating media crossing beam axis between source and patient ; incorrect TPS field implementation (CT numbers, filters ); linac out-put factor variations; incorrect laser calibration.
  • 79. Random error examples • Error in patient setup
  • 80. Random error examples • Error in patient setup •Attenuating median in beam
  • 81. Random error examples • Error in patient setup •Attenuating median in beam • Gas pocket
  • 82. Systematic errors example
  • 83. Set-up verification
  • 84. Old CT Old plan New CT Old plan
  • 85. New RT plan & DIV verification
  • 86. Take Home Message Courtesy of Tufve Nyholm, In Room Imaging and RM planning ESTRO Course 2012
  • 87. Take Home Message Courtesy of Tufve Nyholm, In Room Imaging and RM planning ESTRO Course 2012