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# Random and systematic errors 25.10.12

Random and systematic errors

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### Random and systematic errors 25.10.12

1. 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. 2. Random and systematic errors Courtesy of Tufve Nyholm, In Room Imaging and RM planning ESTRO Course 2012
3. 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. 4. Σ and σ Σ Σ systematic errors -> mean value σ σ random error -> standard deviation
5. 5. Σ and σ Standard deviation: Average value Standard Deviation
6. 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. 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. 8. Effect of errors on dose Random errors blur the cumulative dose distribution CTV Systematic errors shift the cumulative dose distribution CTV
9. 9. Blurred dose Blur planned dose distribution with all errors to estimate the cumulative dose distribution
10. 10. PTV margin
11. 11. What should be the margin?
12. 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. 13. Random and systematic errors Courtesy of Tufve Nyholm, 2012
14. 14. Random and systematic errors
15. 15. Random and systematic errors PHASE Error Correction
16. 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. 17. Registration/Simulation: correction? Prevent!!! Choose!!! Head & Neck Breast Lung / Liver Pelvic
18. 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. 19. Registration/Simulation: correction? Prevent!!! Positioning: comfortable
20. 20. Random and systematic errors PHASE Error Correction SYSTEMATIC • CHOOSE of Immobilization devices • Comfort
21. 21. Target definition/Contouring Wrong delineation of normal tissue Wrong definition of the target target
22. 22. Target definition/Contouring PAST Traditional Simulation PRESENT Virtual Simulation TC per: • contouring target and ORA • creat irradiated volum corresponding to CTV
23. 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. 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. 25. Target definition/Contouring Wrong delineation of normal tissue Wrong definition of the target target Inter-observer Intra-observer
26. 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. 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. 28. Target definition/Contouring Wrong delineation of normal tissue Wrong definition of the target target Inter-observer Systematic Error Intra-observer
29. 29. Target definition/Contouring: correction Optimization!!!  Image quality: Theragnostic CT simulation RM/PET-CT
30. 30. 11 observers from 5 institutions, 22 patients
31. 31. 11 observers from 5 institutions, 22 patients
32. 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. 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. 34. Target definition/Contouring: correction Appropriate Margins Standard? Formula Van Herk? PTV margin = 2.5 Σ + 0.7 σ
35. 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. 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. 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. 38. Treatment design/ Planning
39. 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. 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. 41. Random and systematic errors
42. 42. Radiotherapy treatment process Correct position of the patient (SPACE) every day of the n-days of treament (TIME) … 46
43. 43. Inter-fractional versus Intra-fractional  Inter-fractional – Variation between fractions 47  Intra-fractional – Variation within a fraction
44. 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. 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. 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. 47. Error management Organ Motion/Target Deformation Midcourse replanning Setup protocols Gating Set-up Portal image verification 51 Online vs Offline
48. 48. Off-line correction Correction after treatment RT RT RT RT time
49. 49. On-line correction RT RT RT RT time Correction before treatment
50. 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. 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. 52. Head and Neck Differences in Casts use Coen W. Radiotherapy and Oncology 2001: 105-120
53. 53. Pelvic region Difference in immobilization Devices used Use of skin marks (respiration, weight change) Coen W. Radiotherapy and Oncology 2001: 105-120
54. 54. 6 Degrees of freedom (DOF)
55. 55. 24 pz 209 CBCT & 148 EPID < 2mm > 2° 3,7% prostata 26,4% torace 12,4% Head & Neck
56. 56. 24 pz 209 CBCT & 148 EPID < 2mm > 2° 3,7% prostata 26,4% torace 12,4% Head & Neck
57. 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. 58. 24 pz 209 CBCT & 148 EPID No correlation between the magnitude of translational and rotational setup errors was observed < 2mm
59. 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. 60. Geometrical Data/patients
61. 61. Geometrical Data/patients Pitch! Random error (wide Immobilization device? DS)
62. 62. Geometrical Data/patients
63. 63. Geometrical Data/patients Roll! Systematic error Set up?
64. 64. Geometrical Data/patients
65. 65. Geometrical Data/patients Incremento compliance paziente?
66. 66. Set-up errors SYSTEMATIC RANDOM
67. 67. Set-up errors Sources of errors 1) Mechanic errors (laser) 2) Patient’s errors 3) Immobilization devices 4) Technicians experience
68. 68. Set-up errors SYSTEMATIC GROUPS of patients Mechanic errors (laser) PATIENT
69. 69. Quality Controls
70. 70. Quality Controls: «morning Checkout»
71. 71. Quality Controls
72. 72. Quality Controls
73. 73. Quality Controls SYSTEMATIC GROUPS of patients PATIENT
74. 74. Set-up errors
75. 75. Set-up errors RANDOM PATIENT
76. 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. 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. 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. 79. Random error examples • Error in patient setup
80. 80. Random error examples • Error in patient setup •Attenuating median in beam
81. 81. Random error examples • Error in patient setup •Attenuating median in beam • Gas pocket
82. 82. Systematic errors example
83. 83. Set-up verification
84. 84. Old CT Old plan New CT Old plan
85. 85. New RT plan & DIV verification
86. 86. Take Home Message Courtesy of Tufve Nyholm, In Room Imaging and RM planning ESTRO Course 2012
87. 87. Take Home Message Courtesy of Tufve Nyholm, In Room Imaging and RM planning ESTRO Course 2012