Chapter 12Treatment Planning II: Patient Data,     Corrections, and Set-Up                                       1
12.1 Acquisition of Patient Data (body contours)    Solder wire or lead wire           Contour plotter                    ...
12.1 Acquisition of Patient Data (body contours)1. The contour must be taken with the patient in the treatment position.2....
12.1 Acquisition of Patient Data (internal structures)   Analog conventional tomography: along the long-axis of the body  ...
12.1 Acquisition of Patient Data (internal structures) Analog transverse tomography: transverse cross-section of the body ...
12.1 Acquisition of Patient Data (internal structures)                                  Computed tomography               ...
12.1 Acquisition of Patient Data (internal structures)                                  Computed tomography               ...
12.1 Acquisition of Patient Data (internal structures)                                                         8
12.1 Acquisition of Patient Data (internal structures)     Computed tomographyCT number, Hounsfield number     (µ for kV p...
10
12.1 Acquisition of Patient Data (internal structures)    Magnetic Resonance Imaging (MRI)MRI vs CT:Advantages:    does no...
12.1 Acquisition of Patient Data (internal structures)  Magnetic Resonance Imaging (MRI)                                  ...
12.1 Acquisition of Patient Data (internal structures)     Ultrasound imageUltrasound vs CT:Advantages:                   ...
12.2 Treatment SimulationA simulator duplicates a therapy unit in terms of its geometrical,mechanical and optical properti...
12.3 Treatment Verification Port films: used for treatment/set-up verification.         Simulator image                   ...
12.3 Treatment Verification Port image: used for treatment/set-up verification.                                           ...
12.3 Treatment VerificationElectronic Portal Imaging Device (EPID)        Liquid-ion chamber                              ...
12.3 Treatment Verification Electronic Portal Imaging Device (EPID)         Camera-based                      Solid-state ...
12.3 Treatment Verification   Port image: used for treatment/set-up verification                                          ...
12.4 Corrections for Contour Irregularities         Effective SSD method                                            SSDD A...
12.4 Corrections for Contour Irregularities               TAR (TMR) method          SSD                                   ...
12.4 Corrections for Contour Irregularities   Isodose shift method                                                        ...
12.5 Corrections for Tissue Inhomogeneities   • Changes in the absorption of primary beam and   the associated pattern of ...
12.5 Corrections for Tissue Inhomogeneities       TAR method (equivalent pathlength)                           Dinhom ( P ...
12.5 Corrections for Tissue Inhomogeneities         Power Law TAR method                            Dinhom ( P )   Correct...
12.5 Corrections for Tissue Inhomogeneities            Generalized Power Law TAR method                             Dinhom...
Inhomogeneity correction:                        Generalized Batho Power Law                                              ...
Inhomogeneity correction:                 Generalized Batho Power Law (cont’d)                   ρ1                       ...
Inhomogeneity correction:                               Modified Batho Power Law                   ρ1                     ...
12.5 Corrections for Tissue Inhomogeneities             Equivalent TAR method                                        ~    ...
12.5 Corrections for Tissue Inhomogeneities               Absorbed dose within an inhomogeneity – bone                    ...
12.5 Corrections for Tissue Inhomogeneities        Absorbed dose within an inhomogeneity – soft tissue in bone            ...
12.5 Corrections for Tissue Inhomogeneities Absorbed dose within an inhomogeneity – soft tissue adjacent to bone          ...
12.5 Corrections for Tissue Inhomogeneities Absorbed dose within an inhomogeneity – soft tissue adjacent to bone          ...
12.5 Corrections for Tissue Inhomogeneities Absorbed dose within an inhomogeneity – parallel opposed beams                ...
12.5 Corrections for Tissue Inhomogeneities     Lung tissue and air cavity                    Increased penumbra in lung d...
12.6 Tissue Compensation    Compensator is used to account for surface irregularity or internal    inhomogeneities. Unlike...
12.6 Tissue CompensationDensity or thickness ratio   Due to lateral loss in the air gap ‘d’= h’/h                       be...
12.6 Tissue Compensation                           39
12.7 Patient Positioning                           40
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16 chap 12 treatment planning ii

  1. 1. Chapter 12Treatment Planning II: Patient Data, Corrections, and Set-Up 1
  2. 2. 12.1 Acquisition of Patient Data (body contours) Solder wire or lead wire Contour plotter 2
  3. 3. 12.1 Acquisition of Patient Data (body contours)1. The contour must be taken with the patient in the treatment position.2. A line representing the tabletop must be clearly indicated to serve as a reference.3. Important bony landmarks and beam entry points must be indicated.4. Check body contours during the course of treatment due to possible weight loss and change of tumor volume.5. Take multiple body contours in the sup-inf direction if contours change significantly. 3
  4. 4. 12.1 Acquisition of Patient Data (internal structures) Analog conventional tomography: along the long-axis of the body 4
  5. 5. 12.1 Acquisition of Patient Data (internal structures) Analog transverse tomography: transverse cross-section of the body Takahashi 1950s 5
  6. 6. 12.1 Acquisition of Patient Data (internal structures) Computed tomography 6
  7. 7. 12.1 Acquisition of Patient Data (internal structures) Computed tomography − ∑ µ i ti I = I0 • e i ∑ µ i t i = ln ( I 0 I ) i 7
  8. 8. 12.1 Acquisition of Patient Data (internal structures) 8
  9. 9. 12.1 Acquisition of Patient Data (internal structures) Computed tomographyCT number, Hounsfield number (µ for kV photons) : µ tissue − µ water For Megavoltage photon beams, ComptonH= × 1000 scattering is the dominant event, thus µ water electron density (rather than linear attenuation coefficient in the kilovoltageH air = −1000; H water = 0 range) is more relevant for photon dose calculation. 9
  10. 10. 10
  11. 11. 12.1 Acquisition of Patient Data (internal structures) Magnetic Resonance Imaging (MRI)MRI vs CT:Advantages: does not use ionizing radiation; higher contrast, better imaging of soft tissue tumors.Disadvantage: longer scan acquisition time.MRI is based on proton density and proton relaxation characteristics ofdifferent tissues.Image contrast can be affected by TE (echo time) and repetition time(TR). 11
  12. 12. 12.1 Acquisition of Patient Data (internal structures) Magnetic Resonance Imaging (MRI) 12
  13. 13. 12.1 Acquisition of Patient Data (internal structures) Ultrasound imageUltrasound vs CT:Advantages: Disadvantage:does not use ionizing radiation; poor image quality in some casesReal time.Better contrast in some cases(e.g. prostate) Prostate transducer 13
  14. 14. 12.2 Treatment SimulationA simulator duplicates a therapy unit in terms of its geometrical,mechanical and optical properties, but uses kilovoltage x-ray beam, forbetter image quality. Varian Acuity simulator CT simulator 14
  15. 15. 12.3 Treatment Verification Port films: used for treatment/set-up verification. Simulator image MV port image 15
  16. 16. 12.3 Treatment Verification Port image: used for treatment/set-up verification. 16
  17. 17. 12.3 Treatment VerificationElectronic Portal Imaging Device (EPID) Liquid-ion chamber 17
  18. 18. 12.3 Treatment Verification Electronic Portal Imaging Device (EPID) Camera-based Solid-state detector 18
  19. 19. 12.3 Treatment Verification Port image: used for treatment/set-up verification 19
  20. 20. 12.4 Corrections for Contour Irregularities Effective SSD method SSDD A = Dmax (Q) • Pcorr (?) h dm Q Q’ 90 80 d 70 60D A = Dmax (Q ) • P (d ) A 50 2  SSD + d m Dmax (Q ) = Dmax (Q)   SSD + d + h   m  2  SSD + d m Pcorr = P (d )   SSD + d + h   m  20
  21. 21. 12.4 Corrections for Contour Irregularities TAR (TMR) method SSD SSD h dm Q 90 h 80 90 d 70 d 80 60 70 A” A 60 50 50D" A = Dmax (Q) • P (d + h)D" ∝ T (d + h, rA ) = k • T (d + h, rA ) D A = k • T (d , rA ) Ak = Dmax (Q) • P (d + h) T (d + h, rA ) CF = T (d , rA ) T (d + h, rA ) D A = Dmax (Q ) • Pcorr Pcorr = P" (d + h) • CF 21
  22. 22. 12.4 Corrections for Contour Irregularities Isodose shift method 22
  23. 23. 12.5 Corrections for Tissue Inhomogeneities • Changes in the absorption of primary beam and the associated pattern of the scattered photons • Changes in the secondary electron fluence • For megavoltage x-ray beams, Compton effect is predominant and we can define an effective depth (or equivalent depth, equivalent pathlength) for nonwater equivalent materials 23
  24. 24. 12.5 Corrections for Tissue Inhomogeneities TAR method (equivalent pathlength) Dinhom ( P ) Correction Factor : CF = Dhom ( P ) TAR (d , rd ) d1 ρe = 1 CF = TAR (d , rd ) d2 ρe ≠ 1 d = d1 + d 2 + d 3 ρe = 1 d = d1 + d 2 ρ e + d 3 d3 P rd Equivalent depth 24
  25. 25. 12.5 Corrections for Tissue Inhomogeneities Power Law TAR method Dinhom ( P ) Correction Factor : CF = Dhom ( P ) ρ e −1  TAR (d 2 + d 3 , rd )  d1 ρe = 1CF =    TAR (d 3 , rd )  d2 ρe ≠ 1 d3 ρe = 1 P rd 25
  26. 26. 12.5 Corrections for Tissue Inhomogeneities Generalized Power Law TAR method Dinhom ( P ) Correction Factor : CF = Dhom ( P ) nCF = ∏ [TAR(d − d i −1 , A)] ( ρ − ρ i =1 i i −1 ) d1 ρ1 d2 ρ2where d 0 = 0, ρ 0 = 1 d ρn P rd 26
  27. 27. Inhomogeneity correction: Generalized Batho Power Law ρ1 ρ1 ρ2 z1z z z A ρ =1.0 A A D0 ≈ e − µz D1 ≈ e − µρ1 z D2 ≈ e − µρ1z e − µ ( ρ 2 − ρ1 )( z − z1 ) ≈ T ( z , A) =e − µz − µ ( ρ1 −1) z e ≈ D1T ( z − z1 , A) ρ 2 − ρ1 ≈ D0T ( z , A) ρ1 −1 Note: ρn is relative density to water for layer-n 27
  28. 28. Inhomogeneity correction: Generalized Batho Power Law (cont’d) ρ1 ρ1 ρ2 z1 ρ2 z1 z2 z2 ρ3 ‧‧‧ ρ3 z3z z A A ρnD3 ≈ D2 e − µ ( ρ 3 − ρ 2 )( z − z 2 ) Dn ≈ Dn −1e − µ ( ρ n − ρ n−1 )( z − zn−1 ) ‧‧‧ ≈ D2T ( z − z 2 , A) ρ3 − ρ 2 ≈ Dn −1T ( z − z n −1 , A) ρ n − ρ n−1 N Dn = ∏ [T ( z − z n −1 , A)] n n−1 (ρ −ρ ) CF = D0 n =1 where z0 = 0, ρ 0 = 1 28
  29. 29. Inhomogeneity correction: Modified Batho Power Law ρ1 ρ1 ρ2 z1 ρ2 z1 z2 z2 ρ3 ‧‧‧ ρ3 z3z z A A ρnD3 ≈ D2 e − µ ( ρ 3 − ρ 2 )( z − z 2 ) Dn ≈ Dn −1e − µ ( ρ n − ρ n−1 )( z − zn−1 ) ‧‧‧ ≈ D2T ( z − z 2 , A) ρ3 − ρ 2 ≈ Dn −1T ( z − z n −1 , A) ρ n − ρ n−1 N Dn = ∏ [T ( z − z n −1 + d max , A)] n n−1 (ρ −ρ ) CF = D0 n =1 where z0 = 0, ρ 0 = 1 29
  30. 30. 12.5 Corrections for Tissue Inhomogeneities Equivalent TAR method ~    CF = TAR ( z , r ) r = rρ w(r ) = SAR(r + ∆r ) − SAR (r ) TAR ( z , r ) z ∑ρ w i , j ,k i , j ,k z = ∫ ρ (t )dt ~ ρ=i , j ,k 0 ∑w i , j ,k i , j ,kWi,j,k are weighting factorsin the vicinity of the pointof calculation. Thesummation can be either3D (over i,j,k), or 2D(over i,j, providedmultiple slices have beencoalesced and merged z=0 ρijk z=0 zeffinto a single slice at zeff). 30
  31. 31. 12.5 Corrections for Tissue Inhomogeneities Absorbed dose within an inhomogeneity – bone  µ en  under electron equilibrium : dose = kerma = Ψ •   ρ    µ en   µ en        >    ( ρ e ) bone < ( ρ e ) soft tissue  ρ  bone  ρ  soft tissue 3.19 × 10 26 < 3.31× 10 26 due to photoelectric event due to compton scattering kV MV without bone without bonedose dose with bone with bone soft tissue bone soft tissue soft tissue bone soft tissue depth depth 31
  32. 32. 12.5 Corrections for Tissue Inhomogeneities Absorbed dose within an inhomogeneity – soft tissue in bone ST S If electron fluence is the same, DSTB = DB •   according to Bragg-Gray ρ theory:  B BUnder electron equilibrium, if photon fluence  µ en is the same, dose-to-bone is related to dose- DB = DST •   ρ to-(undisturbed) soft tissue by:   ST The ratio γ of DSTB to DST is: (in general, γ>1) γ = DSTB DST = S ρ( ) • (µ ST B en ρ ) B STIn clinical calculation, the TMR (t ST + ρ B t B )change of photon fluence is DSTB = DST •γ •estimated by TAR or TMR TMR (t ST + t B )ratios: 32
  33. 33. 12.5 Corrections for Tissue Inhomogeneities Absorbed dose within an inhomogeneity – soft tissue adjacent to bone Due to electron backscatter from the bone soft bone tissue 33
  34. 34. 12.5 Corrections for Tissue Inhomogeneities Absorbed dose within an inhomogeneity – soft tissue adjacent to bone >10 MV, increased electron fluence due to pair production in bone soft bone tissue Up to 10 MV, initial buildup of electrons 34
  35. 35. 12.5 Corrections for Tissue Inhomogeneities Absorbed dose within an inhomogeneity – parallel opposed beams 35
  36. 36. 12.5 Corrections for Tissue Inhomogeneities Lung tissue and air cavity Increased penumbra in lung due to increased lateral scattering, effectDecreased dose in Increased dose in lung more pronounced for higher energieslung for small field (for large field size)size, especially forhigh energy due to Increased doseloss of lateral down streamscattering from lung lung homogeneous mediumBuildup immediately beyond the lung-soft tissue interface 36due to lateral loss in lung
  37. 37. 12.6 Tissue Compensation Compensator is used to account for surface irregularity or internal inhomogeneities. Unlike bolus, the compensator is placed 15-20 cm away from the skin to keep skin-sparing effect. 37
  38. 38. 12.6 Tissue CompensationDensity or thickness ratio Due to lateral loss in the air gap ‘d’= h’/h between the compensator and the skin surface, the density/thickness ratio is <1, otherwise, the dose to patient would be too low (over compensated). 38
  39. 39. 12.6 Tissue Compensation 39
  40. 40. 12.7 Patient Positioning 40
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