22 chap 20 intensity modulated radiation therapy

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  • 1. Chapter 20Intensity Modulated Radiation Therapy 1
  • 2. Goals of Conformal Radiation Therapy • Conform dose to the tumor • Reduce normal tissue toxicity • Tumor dose escalation improve local tumor control 2
  • 3. Conventional Conformal Therapy and IMRTConventionalConformal TherapyField shape conforms tothe outline of the target,uniform intensity acrossthe fieldIMRTNon-uniform intensityinside the field to achieveoptimum dose distribution target 3
  • 4. Outline• Optimization (Inverse Planning)• Delivery• Quality Assurance• Clinical Applications 4
  • 5. Inverse Planning Problem xjxj is the intensity of the j-thpencil beam.Find the optimum distribution targetof xj’s (i.e., the optimum iintensity distribution) that willgive the best target coverageand critical organ protection. organ 5
  • 6. Optimization (Inverse Planning)Purpose: To find the ‘optimum’ intensity distribution for all beamsinvolved in a plan that will best meet the planner’s requirements.What are the requirements? Objective functions dose, dose/volume - based, biological indices - based: TCP, NTCPHow to find the optimum solution? Search algorithms deterministic methods stochastic methods(*Optimization is conceptually separated from delivery, so in thisstep we don’t need to be concerned about how it’s to be delivered.) 6
  • 7. (Recent development)Direct Aperture Optimization:To optimize a set of apertures (shape and weight) toachieve the best dose distributions.Advantage: eliminates the step of leaf-sequencing;optimized results = deliverable results.(In fluence optimization, the optimal fluencedistribution may not be deliverable, due to limitationsof leaf transmission.) 7
  • 8. Objective Functions based on Dose, Dose/Volume• Examples of commonly used objective functions: Etarget: (D-P)2 2critical organs: (D-Dc)2, (D-Dc) if D>Dc cdose volume conditions: no more than p% of the volume to exceed dose q.• Reasonable and mathematically convenient.• No fundamental physical basis.• Could be any other forms such as |(D-P)m|. 8
  • 9. Objective Function Based on Dose and Dose/Volume target Serial type Parallel type Normal tissue Normal tissue 2 2wl (D-P ) l (D-Dc) No more than p V % of the volume to 2 wu(D-P ) exceed dose q. u p% q D P P l u Dc Dose constraint Dose/volume constraint 9
  • 10. Objective Functions based on Biological Indices• Maximize TCP, minimize NTCPs.• Used in place of or in conjunction with dose-,dose/volume-based objective functions.• At present, clinical data are scarce and modelsnot well-established yet.• Not available on commercial system at present. 10
  • 11. Examples of Optimization Methods• Deterministic: DGradient, Conjugate gradient (Eclipse,Konrad). ) Maximum likelihood (Brainlab, nuclear medicine).• Stochastic: SSimulated annealing (NOMOS). ) Genetic algorithm (Brachy therapy). 11
  • 12. Prostate IMRT plan5-field to 81 Gy 12
  • 13. Global vs. Local Minimum (example of local minima) Objective Function 1 Uniform target dose (100% dose): 1 solution, beams 1&2 equally weighted. target2 Critical organs: no more than 1/2 to exceed 50% dose. 1 solution, beams 1&2 equally weighted. crit. org. Critical organs: no more than 1/2 to exceed 10% dose. 2 solutions, beams 1&2 weighted either (a,b) or (b,a) ⇒ local minima !! 13
  • 14. Two-dimensional grey-scale display of the objective function Fobj as a function of beam weight 1 and beam weight 2 1.5 1.5 Fobj = 1404.5 at (0.24,1.5) 1 1 Fobj = 0 Beam 2Beam 2 at (1,1) Fobj = 745.7 at (1.5,0.35) 0.5 0.5 (a) (b) 0 0 0 0.5 1 1.5 0 0.5 1 1.5 Beam 1 Beam 1 Only dose uniformity in the Dose uniformity in the target target is required plus dose/volume constraint to the critical organ is required 14
  • 15. Global Minimum• In Principle: I Stochastic methods can find global minimum. SDeterministic methods may get trapped in local minima.• In Practice: I It is not easily known if current solution is at global or local minimum, regardless of which methods are used. . It may not be important if the solution is clinically satisfactory. s If solution not satisfactory: ♦ for stochastic methods: change random selection parameters (e.g.annealing schedule), increase number of iterations. ♦ for deterministic methods: try different initial guess. ♦ is the new solution better? 15
  • 16. Dose Uniformity in the TargetIMRT vs Conventional Conformal PlansThere is no Is itno issue. important ? yes IMRT should do better (at least no worse), for there are more degrees of freedom. 16
  • 17. Dose Distributions IMRT vs Conventional Conformal Plans target 105 100 70 45°45° Wedged pair IMRT pair 17
  • 18. Dose Volume Histograms IMRT vs Wedged Pair 100 80 IMRT Wedged PairVolume (%) 60 40 target 20 rest of volume 0 0 20 40 60 80 100 120 Dose (%) 18
  • 19. Intensity Profiles Produced from Inverse Planning without smoothing• Local fluctuation in intensityprofile, due to numerical artifact.• Difficult to deliver, requires longerbeam-on-time.• Susceptible to treatmentuncertainties. 19
  • 20. Smoothing of beam profiles• Smooth outside objective function (at the end of each iteration) – General method; independent of the objective function – Cannot distinguish between clinically relevant gradients and artifacts• Smooth inside objective function – Depends of particular form of objective function – Dosimetric consequences of smoothing accounted for in optimization. 20
  • 21. Smoothing of Intensity Profiles Methods of smoothing: • Median window filter (webb, PMB 43:2785, 1998) • Savitzky-Golay (least squares fit) median window filterSavitzky-Golay(least squares fit) before smoothing after smoothing (with S-G) 21
  • 22. Smoothing Included as Part of the Objective Function.Fobj = ∑ w (D − D ) i∈target i i p 2 For over & under dose in the targets For over dose in critical organs, may include dose-volume conditions For smoothness in intensity profile
  • 23. Example 1: Phantom PTV OAR PTV 100 5 100Smoothing at the end of Smoothing within the each iteration objective function 23
  • 24. PTV x Brainstem 95 50 30Smoothing at the end of Smoothing within the each iteration objective function 24
  • 25. 100 100 80 PTV 80Volume (%) 60 60 40 Cord 40 Brainstem 20 20 0 0 0 20 40 60 80 100 120 0 10 20 30 40 50 60 70 Dose (%) Dose (%) Smoothing at the end of each iteration Smoothing within the objective function No smoothing 25
  • 26. The ‘Skin-Flash’ Problem in Inverse PlanningConventional:Margin added to fieldedge to allow foruncertainties.IMRT: PTVIntensity remains at 0outside PTV. No skin-flash
  • 27. Skin-Flash for Intensity-Modulated Field Simple, flat extension skin
  • 28. Detection of unexpected hotspots Beam IBeam II A PTV B PTV Cord Beam III Hotspots > 120% location > 3 cm from PTV 28
  • 29. Detection of unexpected hotspots• IMRT may produce hotspots outside the PTV – Can be at large distances from the PTV.• Hotspots may not be appear at the standard three orthogonal planes used for plan evaluation – May be worse for non-coplanar beams• Proposed solution: – Use volume display to detect possible hotspots – “Rind” = annular region around the PTV – “Rest-of-body” = “irradiated body” - PTV - OARs – Efficiency issues: “Rest-of-body” is a large structure and fine calculation grid is required 29
  • 30. Summary - Optimization• Objective functions may be based on dose, dose/volumeconditions, or biological indices.• Optimization methods may be stochastic or deterministic.• Local minima may exist, but there is no easy way to tellwhether a solution is at a global or local minimum, regardlessof which optimization method is used.• Optimized intensity distribution should give better dosedistribution than conventional conformal plans.• A typical case involving 103 rays, and 104 points, takes about3 to 10 minutes of computer time with the gradient method. 30
  • 31. Summary – Optimization (practical considerations)• smoothing is necessary to reduce unnecessary fluctuations inintensity distribution.• skin flash is needed to account for treatment uncertainties(breast, head/neck).• beware of unexpected hot spots. 31
  • 32. Delivery of IMRT• Compensator: less efficient (fabrication, re-entryinto the room between fields).• Fixed field with conventional MLC: Fcontinuous leaf motion, cstep-and-shoot.• Rotational field: Rconventional MLC, cNOMOS/MIMIC, Tomotherapy. 32
  • 33. MIMiCMultileafIntensityModulatingCollimator 33
  • 34. Individual leaf controls openingMIMiCMultileafIntensityModulatingCollimator 34
  • 35. Tomotherapy 35
  • 36. Delivery of IMRT with a Multileaf Collimator (MLC)MLC mounted on the head of a linac Close-up view of the leaves 36
  • 37. Delivery of IMRT with a Conventional MLC sliding window method radiationbeam-ontime direction of motion Right-leaf Left-leaf P 37
  • 38. Methods - Sliding Window Techniques Dynamic vs. Segmental (step-and-shoot) Dynamic Segmental T dBeam-on-Time d Left-leaf T c Left-leaf Right-leaf c Right-leaf b b delivered intensity delivered intensity a a ∆t 1 1 X X = ≤ v=∞ ∆x v vmax P P 38
  • 39. The Posterior Field in a Prostate Treatment 39
  • 40. An Intensity-modulated Field Delivered with a Conventional MLC For cordprotection 40
  • 41. Practical Considerations• Maximum leaf speed - approx. 2.5 cm/sec on Varian MLC• Leaf transmission - approx. 1.5% on Varian MLC• Leaf edge effect - rounded leaf end on Varian MLC• Source distribution - variation of output with fieldsize & shape• Tongue & groove effect•Maximum leaf protrusion/retraction on each side -14.5 cm on Varian MLC• very low intensities not deliverable 41
  • 42. Tongue-and-groove Effect BEAM• Varian MLC employs a tongue-and-groove groove tongue design to reduce leakage between leaves• Leaf synchronization – Van Santvoort 1996 – Webb 1997 – Longer beam-on time 50% 42
  • 43. Splitting Large IM fields• Maximum Varian DMLC width ~ 15 cm• Larger fields (e.g. NP) split into 2 or 3 subfields• Considerations: – Smoothness of profiles; no discontinuities – Split along a straight line or a low intensity region – Use feathering to reduce effects of uncertainties 43
  • 44. Desired and Delivered Intensity Profiles desired delivered 25 20intensity (MU) 15 10 5 0 -8 -6 -4 -2 0 2 4 6 8 x (cm) 44
  • 45. Comparison of DMLC and SMLC Methods DMLC: • accurate delivery of the desired intensity profiles. SMLC or Step-and-shoot: • User more comfortable - resembles multi-segment conventional treatment. • Shorter beam-on-time (MU) compared to DMLC. • Longer delivery time (min.) compared to DMLC. (on some machines) • Loss of spatial & intensity resolution 45
  • 46. Conversion fromcontinuous to discrete intensity profiles Continuous Equispaced multi-level intensity profile intensity profileResolution : x = 2 mm Resolution depending on the intensity = continuous number of levels 46
  • 47. DVH comparison between DMLC and a 5-level SMLC delivery for a prostate case 120 DVH Comparison 100 PTV DMLC 80volume (%) 5-level SMLC 60 x-grid = 2 mm rectum 40 20 bladder femur 0 0 20 40 60 80 100 120 dose (%) 47
  • 48. DVH comparison between DMLC and a 5-level SMLC delivery for a head/neck case DMLC 5-level SMLC x-grid = 2 mm 120 30 PTV 100 25 80 20volume (%) intensity (MU) 60 15 cord 40 10 20 5 0 0 0 20 40 60 80 100 120 -10 -8 -6 -4 -2 0 2 4 6 8 10 dose (%) x (cm) DVH comparison Delivered profile 48
  • 49. Combined DMLC and SMLC Delivery Introduction of Beam-off Segments DMLC DMLC/beam-off segmentTo deliver very low intensity To deliver very low intensity,(e.g. cord block), opposing introduce a beam-off segmentleaves touch each other & move while leaves move from a to b.at maximum speed from a to b. T T T’ Left leaf Left leaf TimeTime Right leaf Right leaf F(x) F(x) 0 x x2 0 x x2 1 a b X 1 a b X 49
  • 50. Leaf Pair 14 Desired intensity profile Delivered intensity profile Left leaf path Right leaf path Without beam-off segment With beam-off segment100 10090 9080 8070 7060 6050 5040 4030 3020 2010 10 0 0 -10 -5 0 5 10 -10 -5 0 5 50 10
  • 51. Summary - Delivery• Intensity-modulated field can be delivered with aconventional MLC using the Sliding Window Technique,either in dynamic (DMLC) or segmental (SMLC or step-and-shoot) mode.• Capable of delivering (almost) any shape of intensityprofile, but limited by leaf speed, transmission, etc.• Need to account for leaf transmission, rounded leaf end,and head scatter.• Split large field into 2 or more segments, if necessary. 51
  • 52. Summary - Delivery (cont’d)• Loss of beam-on-time efficiency relative to conventionalfields due to small field openings. ◊ prostate : 2~3 times ◊ nasopharynx: 3~4 times ◊ breast: about the same• Treatment time equal or less than conventional treatment, e.g.,5-field prostate treatment < 8 min. (excluding patient setup).• Delivery with SMLC requires less beam-on-time (MU), butlonger delivery time (min) than that with DMLC (on somemachines).• Delivery with SMLC should avoid segments of short beam-on-time for concerns of beam stability. 52
  • 53. The Effects of Intra-Fraction Organ Motion on the Delivery of Intensity-Modulated Fields with a Multileaf Collimator• For conventional treatment, the entire treatment field is exposedduring a fraction.• For IMRT, the treatment field is divided into many sub-fields, ofwhich only one sub-field is exposed at a time. Consequently, ifthere is organ motion during treatment, portions of the treatedvolume may move in and out of the sub-field during a fraction.• Since leaf sequence is designed based on a static geometry, thepresence of organ motion will cause the actual delivered intensityprofile to be different from the planned one.
  • 54. Organ Motion Relative to Leaf Motion Parallel Perpendicular T d d’Beam-on-Time Left-leaf c’ Right-leaf c b’ b Desired intensity a a’ X Y P P
  • 55. Intra-fraction Breathing Motion (Breast Treatment) A = ±3.5 mm, τ = 4 sec. organ motion  leaf motion Leaf pair #14: average gap = 4.51 cm. Single fraction Averaged over 30 fraction planned profile ******* delivered profile, motion averaged over 30 fx
  • 56. Intra-fraction Breathing Motion (Breast Treatment) A = ±3.5 mm, τ = 4 sec. organ motion  leaf motion 105 103 100 50 IMRT static IMRT motion averaged over 30 fx
  • 57. Intra-fraction Breathing Motion (Lung Treatment) A = ±7.0 mm, τ = 4 sec. organ motion ⊥ leaf motion planning images acquired1 cm planned profile ******* delivered profile, motion averaged over 30 fx
  • 58. Intra-fraction Breathing Motion (Lung Treatment) A = ±7.0 mm, τ = 4 sec. organ motion ⊥ leaf motion planning images acquired 105 100 90 50 20 IMRT static IMRT motion averaged over 30 fx
  • 59. Intra-fraction Breathing Motion (Lung Treatment) A = ±7.0 mm, τ = 4 sec. organ motion ⊥ leaf motion planning images acquired 120 100 GTVvolume (%) 80 static PTV 60 motion lungs 40 20 0 0 20 40 60 80 100 120 Dose (%)
  • 60. Summary of Effects of Intra-fraction Organ Motion • Effects of intra-fraction organ motion can be calculated, provided the pattern of motion is known. • Effects can be calculated for single or multiple fractions. • For breast treatment, if the amplitude < 3 ~ 5 mm, effects appear to be insignificant over multiple fractions. • Penumbra broadening at field edge is common to both conventional and intensity-modulated fields. • If in-field effects significant, alternative means will be needed, e.g., compensator, breath hold, gating.
  • 61. Quality Assurance• Machine Performance (DMLC): : Film test FGap test• Machine Performance (Step-and-Shoot): : Dose/MU vs. MU D Flatness, symmetry vs. MU• Patient Dosimetry: : Record & verify, file check-sums (each fraction) ( Independent MU check, portal image (each patient) ( Log file analysis, chamber measurement, film dosimetry (periodically or new software, technique, or site) 61
  • 62. Film test1 mm bands errors introduced ← - 0.5 mm ← - 0.2 mm ← + 0.2 mm ← + 0.5 mm 62
  • 63. Gap error → Dose error 20.0 Range of gap width 15.0% Dose error Gap error (mm) 10.0 2.0 1.0 5.0 0.5 0.2 0.0 0 1 2 3 4 5 Nominal gap (cm) 63
  • 64. Gap Test 100 MU Gap error → Dose error 5mm gap 20.0 Range of gap width 15.0 chamber% Dose error Gap error (mm) 10.0 2.0 1.0 5.0 0.5 0.2 0.0 0 1 2 3 4 5 64 Nominal gap (cm)
  • 65. DMLC Output vs Gantry / Collimator Angles 1.03 1.03 1.02 1.02Relative output 1.01 0.2 mm 1.01 1.00 1.00 0.99 0.99 0.98 0.98 245 0-0 445 0.97 90-0 0.97 8 8 270-0 7 7 8 8 8 8 8 7 7 8 8 t-9 ov-9 n-9 pr-9 n-9 ug-9 ct-9 8 180-0 t-9 ov-9 an-9 pr-9 n-9 ug-9 ct-9 Oc N Ja A Ju A O Oc N J A Ju A O 90-90 Date 270-90 Date 65
  • 66. Beam Stability: Dose per MU• Iso-centric setup, farmer- type ion chamber, in solid water phantom• Checked both short and long term stability.• For > 2MU, dose per MU is within +/- 2%. For > 2MU, dose per MU is within +/- 2%. 66
  • 67. Beam Stability: Flatness, Symmetry 0.1 0 GUN-TARGET DIRECTIONS ymmetry CROSS-PLANE DIRECTION 0.05 0.00 -0.05 0.1 0Flatnes s 0.05 0.00 -0.05 1 10 1 00 Total MUs Delivered 67
  • 68. Measured vs Calculated Sum of 5 IMRT fields 1.03 1.02Dmeas / Dcalc 1.01 1.00 Linac-1 0.99 Linac-2 0.98 0.97 0.96 mean = 0.993, s = 0.008 0.95 0 100 200 300 400 Patient # 68
  • 69. Port Film for Intensity-Modulated FieldUse left leaves of first segment and right leaves of lastsegment as the port film field. IMRT field Port film 69
  • 70. Dose Reconstruction from Log & DVA Files Nasopharynx - Rt Lateral Overlay Dose differences (log-dva) dva dva log filelog file 70
  • 71. Log File Analysis 1 Dose 0.2 0.9 max = 32 cGy 0.15 0.8 B 0.1 Dose Difference (cGy) 0.7 A 0.05 0.6MU fraction 0.5 0 0.4 -0.05 0.3 -0.1 0.2 0.1 -0.15 0 -0.2 -8 -6 -4 -2 0 2 4 6 8 Distance from axis (cm) 71
  • 72. Independent Verification of IMRTA good QA practice. In the US, it may also be a regulatoryrequirement. For IMRT, hand calculation is impractical, anindependent verification program is needed. Leaf sequence file, beam-on-time, input jaw settings, machine data table. Including effects of scattered source, rounded leaf end, Calculate delivered mid-leaf & between-leaf transmission,intensity distribution tongue-and-groove effect, and scatter from the leaves. Calculate dose Calculate dose (cGy) . 72
  • 73. Calculation of Delivered Intensity DistributionLeaf sequencing file: describes leaf positions as a function ofbeam-on time (MU).Step-and-shoot time T1 T2 T3 T4 Leaf positions + + + + dynamic time 0 T Leaf positions + ••• + ••• + •••+ 73
  • 74. Between leaf transmission Tongue-and/or-groove effect BEAM BEAMgroove tongue 74
  • 75. Ring-shaped Field first segment second segment 75
  • 76. Varian Clinac-2100C MLC tongue & groove 76
  • 77. Intensity distribution in the penumbra region as a functionof the distance from the rounded leaf end. beam mid-leaf Rounded leaf-end tongue or groove 1 direct exposure under mid-leaf 0.8 under tongue or groove intensity 0.6 0.4 0.2 under the leaf 0 ε -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 77 distance from the leaf-end (cm)
  • 78. Variation of Output with Field Shape/Size Backprojection to the Source Plane Source plane MLC opening MLC plane Isocenter plane (x,y)  1 if ( x, y ) inside opening φi = ∫∫ Oi ( x , y ) S ( x − x , y − y )dx dy Oi ( x, y ) =  source  0 if ( x, y ) outside opening φ = ∫∫ φ ( x , y ) S ( x − x , y − y )dx dy φ = ∫∫ source Oi ( x , y ) S ( x , y )dx dy i source =φ ⊗S 78
  • 79. Scattered Intensity from the MLC – For large fields can contribute up to 5% intensity Pencil beam 1.5 to 2% transmission leaf Scatter fromScatter from the leafthe leaf 10 5 0 5 10 transmission Distance from pencil beam 79
  • 80. Scattered Intensity from the MLC Source plane intensity Scattered intensity from the leaf Smlc MLC opening 10 5 0 5 10 MLC plane Distance from pencil beam φmlc ( x, y ) =Isocenter plane ∫∫ B( x , y )S isocenter mlc ( x − x , y − y )dx dy plane  0 if ( x, y ) inside opening φmlc = B ⊗ S mlcBi ( x, y ) =   1 if ( x, y ) outside openingB ( x, y ) = ∑ Bi ( x, y )∆ti 80 i
  • 81. Dose Calculation Algorithm for IM Fields Pencil Beam Convolution pencil beam Intensity-modulated field d1 d2 pencil beam kernel dose distribution 81
  • 82. Comparison Between Calculation and Measurement Film Calc. Tongue-and-groove Between leaf transmission 82
  • 83. A Field used in a Nasopharynx Treatment Sup 6 MVxAnt Post Film Plan Inf 83
  • 84. 7-field Nasopharynx - cylindrical phantom/coronal 84
  • 85. Dosimetry (Lung - PA field) 2 cmPlanFilm Film - Plan Overlay Difference 85
  • 86. Lung PA-field: Dose difference (film – calc.) MLC scatterT&G Source 86
  • 87. Milestone of IMRT at MSKCCOct. 95: 1st IMRT (boost) at MSKCCSpring 96: Prostate 81 Gy, all IMRT (5 fields)*96-97: Prostate 86 Gy, all IMRT (5 fields)98: Head / Neck99: BreastTo date: over 2,000 prostate, H/N, breast, and other IMRT patients *Has become Standard Treatment 87
  • 88. IMRT for Prostate History: Prostate Dose Escalation Study 7020 - 7560 - conventional8100 - conventional and IMRT (with rectal sparing) ~ 500 patients with IMRT 8640 - IMRT (with rectal sparing) 40 patients 9180 - IMRT (with rectal and urethra sparing) 88
  • 89. 81-Gy Prostate Plans – 3D Conformal Plan 6-field to 72 Gy, 6 cone-down fields to 81 Gy Rectal wall target bladder wall 89
  • 90. 3D Conformal Plan - Prostate 81 Gy 100 D=77Gy V=90% 75Volume (%) D=75Gy 50 V=30% target bladder 25 rectum femurs 0 0 25 50 75 100 Dose (Gy) D=72Gy 90
  • 91. 81 Gy - Transverse8640 8100 7560 5000 2500Conventional Plan IMRT Plan 91
  • 92. Prostate 81-Gy Plans 100 100 standard 100 optimizedVolume (%) 75 75 75 50 50 50 25 target 25 25 rectum 0 70 80 90 0 0 0 25 50 75 100 0 25 50 75 100 100 100Volume (%) 75 75 50 50 25 bladder 25 femur 0 0 0 25 50 75 100 0 25 50 75 100 Dose (Gy) Dose (Gy) 92
  • 93. PSA Relapse-free Survival in Unfavorable Patients by Dose 100 81 Gy (65) 75.6 Gy (193) Percent PSA Relapse-free Survival 64.8-70.2 (134) 80 66 % 60 p=0.05 43% 40 p=0.006 21% 20 Unfavorable T1-3 PSA >10; Gleason >7 0 0 12 24 36 48 60 72 84 96 108 Months 93
  • 94. Grade 2 Rectal Toxicity by Dose 80 20 75.6 Gy (446)Percent Grade 2 Rectal Toxicity 81 Gy (61) 15 85 10 90 p< 0.001 64.8-70.2 Gy (364) 595 81 Gy IMRT (171) 0 24 48 72 96 120 Months 94
  • 95. Nasopharynx Traditional Treatment e e50 Gy70 Gy77 Gy PTV Cord, Brainstem 95
  • 96. MSKCC Conformal Treatment50 Gy70 Gy77 Gy PTV Cord, Brainstem 96
  • 97. IMRT Treatment50 Gy70 Gy77 Gy PTV Cord, Brainstem 97
  • 98. Comparison of nasopharynx treatment techniques 50 Gy 70 Gy 77 Gy Traditional Conformal IMRT 98
  • 99. Posterior Field in a Nasopharynx Treatment 99
  • 100. Nasopharynx IMRT 100
  • 101. 3D dose display of the 65 Gy isodose surface IMRT 3D Conformal Traditional Spinal cord/Brain stem Eye PTV 101
  • 102. 100 100 CORD 80 PTV 80%VOLUME 60 60 40 40 Conf . Conf . 20 Trad . 20 Trad . IMRT IMRT 0 0 0 2000 4000 6000 8000 0 2000 4000 6000 8000 DOSE (cGy) DOSE (cGy) 100 100 MANDIBLE 80 80 PAROTID%VOLUME 60 60 40 40 Conf. Conf . Trad. 20 Trad . 20 IMRT IMRT 0 0 0 2000 4000 6000 8000 0 2000 4000 6000 8000 102 DOSE (cGy) DOSE (cGy)
  • 103. Plan ComparisonPlan PTV Cord Mandible Time Mean V95 Max. Max V95 Plan TreatTrad. 68 Gy 79% 48.5 Gy 77 Gy 27% 1h 0.4 hConf. 73 Gy 97% 47.5 Gy 82.5 Gy 18% 12 h 0.75 hIMRT 76 Gy 99% 39.0 Gy 77 Gy 9% 8h 0.5 hAvg. for 3 patients 103
  • 104. Fusion of CT, MRI, and PET Scans for IMRT Planning 104
  • 105. Parotid Sparing in 100 N0 disease 80 %Volume 60 PTV54 40 No PS 20 PS 0 0 20 40 60 80 Dose (Gy) 100 80 PAROTID %Volume 60 No PS PS 40 2030 36 42 48 54 Gy 0 0 20 40 60 80 PTV 54 Parotid Dose (Gy) 105
  • 106. Optimization Parameters and Target -Normal Tissue Proximity 100 PTV70 80 % Volume 60 40 Lt. Cochlea 20 040 47 55 63 70 Gy 0 20 40 60 80 Dose (Gy) PTV 70 PTV 54 Cochlea 106
  • 107. IMRT for Nasopharynx – Hong Kong 107Kam et al, IJROBP 60, 1440 (2004)
  • 108. IMRT for Head/Neck - Finland Stimulated secretion 108Saarilahti et al, Radiother Oncol 74, 251 (2005)
  • 109. Breast Plans - IMRT vs. Wedged Pair 108 104 100 90 50 10Wedged pairIMRT 109
  • 110. DVH: Coronary Artery Region 100 80 Standard Intensity ModulatedVolume (%) 60 40 20 0 0 20 40 60 80 100 120 Dose (%) 110
  • 111. DVH: Contralateral Breast Standard IMRT Dose (%) 111
  • 112. Breast Plan Comparison PLAN PTV Ipsilateral Lung Arteries Max. Dose V50 V100 Mean Dose IMRT 112% 12.5% 6.6% 21.3% Conv. 120% 14% 10.2% 32%Avg . for 10 patients 112
  • 113. CTI/Siemens PET/CTCT PET PET/CT 113
  • 114. RPM Respiratory Gating System Infrared camera Reflective respiration monitorFirst RG-IMRTprotocol patienttreated in On/off beam gateOctober, 2001 114 Control workstation Treatment machine, CT, or PET
  • 115. IMRT 3DCRT 115
  • 116. IMRT vs. 3DCRT: DVH for lungs and PTV IMRT 3DCRT 116
  • 117. Whole Abdomen Treatment (planning study only) Target: whole abdomen. Critical Organs: bones, kidneys, liver. conventional IMRTAP-PA Standard distanceExtended distance Two isocenters Nine fields 117
  • 118. Whole Abdomen - Isodose Distributions108 100 90 60 50 coronal sagittal 118
  • 119. IMRT AP-PAPTV KidneysLiver Bones 119
  • 120. Summary• Optimized IMRT plans can produce better dose distributionsthan conventional conformal plans, in terms of both targetcoverage and normal organ sparing.• Delivery of IMRT with a conventional MLC is practical,either in continuous or in step-and-shoot mode.• Comprehensive QA is needed, for machine performance andpatient-specific dosimetry.• IMRT has been implemented for prostate, head/neck, breastand other sites. Early experience on prostate and nasopharynxthus far show encouraging results. 120