Optimal Use of Emerging g Technologies

Transcription

1 Optimal Use of Emerging g Technologies Radhe Mohan, PhD Professor and McNeil Endowed Chair Department of Radiation Physics 1

2 Optimal Use of Emerging Technologies A perspective Complexity and sophistication of emerging technologies often exceed our ability to use them optimally Technologies may have great potential but the state of the art may be insufficiently advanced or we may not have adequate knowledge, skills and tools to use them optimally Consequence: Even though h a new technology may appear to be promising, the promise may not tbe realized or may be delayed d 2

3 Safe What Does Optimal Use Mean Effective - leading to substantially improved therapeutic ti ratio Accurate - What you see is what you get Efficient and affordable 3

4 Definition of Emerging g Technologies (Business Dictionary) New technologies that are currently developing or will be developed over the next five to ten years IMRT? Proton therapy? VMAT? IGRT? Adaptive RT? 4

5 When a New Technology Emerges Claims are made about its superior potential Part of it is hyperbolic sales pitch Technology evolves over time as ways to improve it are discovered Techniques to use a new technology improve with experience 5

6 The Main Point Optimal use of any technology is a moving target 6

7 IMRT Still Emerging 7

8 IMRT Current efforts towards optimal use of IMRT Multi-criteria optimization Optimization of parameters of objective functions ( Auto Planning ) Beam angle optimization The above are virtually impossible to achieve though trial and error Robust optimization - Achieving what you see is what you get in the face of uncertainties Volumetric Modulated Arc Therapy (VMAT) 8

9 Multi-Criteria Optimization Main purpose: Improving efficiency However, efficiency and optimality are intertwined 9

10 Multi-Criteria Optimization Based on Pareto s economic theory Applied to radiotherapy it means that, once Pareto optimality is reached, plan characteristics corresponding to one objective cannot be improved without worsening the plan characteristics corresponding to one or more of the other objectives Database of plans for a range of each subobjectives is generated Database interactively navigated by the treatment planner tradeoff competing objectives 10

11 Multi-Criteria Optimization Courtesy - Bortfeld (in collaboration with RaySearch) 11

12 Robust Optimization Making treatment plans less sensitive to uncertainties 12

13 Robust Optimization Most important for proton (and particle) therapy because of its high sensitivity to uncertainties Method Incorporation of uncertainty distribution within optimization Requires knowledge of uncertainty t distributions ib ti Cost: May lead to higher normal tissue doses compared to a nominal plan Benefit: Greater confidence that dose distribution planned is delivered 13

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16 Robust Optimization Another Approach Nominal ΔU +ΔU 16

17 IMPT Robust Optimization of a Base of Skull Case CTV Optic Chiasm CTV max Brainstem To evaluate for hot spots Robust optimization Optimization includes uncertainties Nominal plan evaluated for robustness Liu, Zhang, Mohan 17

18 VMAT VMAT (RapidArc) introduced with great fanfare 18

19 Ling et al, Commissioning & QA of RapidArc RT, IJROBP 72, , Requires only one gantry rotation and produces dose distributions equivalent to or better than those of IMRT Claim that RapidArc is: More conformal than IMRT 5 to 15 times more efficient than Tomotherapy IMAT (precursor of VMAT or RapidArc) produces dose distributions that are highly conformal and are equal to or superior to those generated by tomotherapy in majority of cases 19

20 Mehta, Mackie LTE Absence of data does not constitute proof; - IJROBP 75, 4-5 Vehemently disagreed 20

21 The Truth of the Matter is Multi-Field IMRT IMAT Tomotherapy (VMAT) RapidArc Are all different forms of IMRT Optimality (quality of plans, accuracy, efficiency of delivery) may depend on The treatment site Stage of evolution of technology and techniques And on planner s experience, expertise, 21

22 Yougainherebutyouloseelsewhere elsewhere Adapted from For rotational beams, dose falls to ~50% at 5 cm For static beams, dose falls laterally much more steeply but less along the beam axis 22

23 Optimality of a static-field IMRT, VMAT or Tomotherapy Plan Depends, in part, on the degree of modulation All modalities allow different and multiple l ways achieve as much modulation as desired IMRT though larger number of beams VMAT through slowing down the gantry, increasing i leaf speed and/or through h multiple l arcs Tomotherapy through optimally reduced pitch The choice of S-IMRT vs. rotational modalities should be based on clinical considerations of different dose distributions 23

24 Treatment Delivery Efficiency Multiple-static field IMRT can be as efficient as VMAT Multiple l fields may be delivered d automatically ti without moding up or down Implemented in the new Varian machine VMT and S-IMRT allow selection from wide range of apertures shapes and sizes and have the flexibility to maximize the aperture sizes Larger aperture sizes mean a lower number of monitor units and more rapid delivery 24

25 Current State of the Art of VMAT is Suboptimal for Many Clinical Situation For instance, considerable trial and error is necessary to define pseudo structures to chase hot and cold spots to other locations or to redistribute them Continuing i R&D is likely l to improve algorithms and consequently optimality 25

26 2 Arc VMAT plan by Physicist 740 MUs 2 Arc VMAT plan by MDACCAuto Auto Plan 951 MUs Norma lized vo olume (% %) PTV Bladder Rectum Dose (cgy) Quan, Zhang, et al 26

27 VMAT plan by VMAT plan by Physicist MDACC Auto Plan 740 MUs 951 MUs 76 Gy 65 Gy 45 Gy PTV rectum bladder femoral heads 30 Gy 27

28 Proton Therapy Another Emerging Technology Though it has been around for 50 years 28

29 Has great potential Proton Therapy State of the art is not as advanced as photons Protons (and particles in general) are more sensitive to inter- and intra-fractional variations in anatomy and set up and to uncertainties related to CT numbers Dose computation ti algorithms are inadequate Radiobiological effectiveness is not well understood and approximations used may be too simplistic Technology and techniques to apply PT are is not as mature as for IMRT Consequences: What you see on a plan may be Suboptimal and Quite different from what is delivered Optimal use requires further R&D and experience 29

30 Proton Therapy Optimality An Illustration 30

31 Randomized Trial to compare PSPT vs. IMRT with concurrent chemo for LA NSCLC Abi bi-institutional institutional Phase II Bayesian adaptively randomized trial Initial concerns - Ethics Primary objective: Inter-compare the incidence & time to development of grade > 3 TRP or to loco-regional recurrence, whichever occurs first 31

32 Planning Considerations PSPT & IMRT plans are designed at 74 Gy (RBE) If PSPT and IMRT plans cannot be achieved at this level, modality allowing higher dose is used Planning objectives: 99% PTV receiving i 95% of the prescribed dose Normal lung V20 37%; mean lung dose (MLD) 22 Gy (RBE) 1/3, 2/3, whole esophagus 65, 55, 45 Gy (RBE) 1/3, 2/3, whole heart 60, 45, 30 Gy (RBE) Spinal cord max 50 Gy (RBE) 32

33 IMRT vs. PSPT for LA NSCLC Randomized Trial Is there Equipoise? Results (First 36 Patients t Enrolled) Dose level of 74 Gy (RBE) achieved within allowed deviation for ~ 2/3 rd of the patients for both IMRT and PSPT without violating normal tissue constraints For 22 / 36 and 8/36 patients, higher h dose could be delivered d with IMRT and protons respectively and there were 2 ties Proton IMRT 8000 Do ose (CGE) Patient 33

34 IMRT vs. PSPT for LA NSCLC Randomized Trial Is there Equipoise? Results (First 36 Patients t Enrolled) Lung V statistically superior for IMRT than for PSPT Lung V 5, V 10, mean heart dose, and cord maximum dose superior for PSPT than for IMRT MLD and all other dose and dose-volume indices were indistinguishable Lung Normalized DVH Data 5000 PSPT IMRT 4000 Mean Dose Parameters PSPT IMRT Dose (CGE) PSPT:V5 IMRT:V5 PSPT:V10 IMRT:V10 PSPT:V20 IMRT:V20 PSPT:V30 IMRT:V30 PSPT:V40 IMRT:V40 PSPT:V50 IMRT:V50 PSPT:V60 IMRT:V60 PSPT:V70 IMRT:V70 PSPT:AVG GESO IMRT:AVG GESO PSPT:AVGLU LUNG IMRT:AVGLU LUNG PSPT:AVGHE EART IMRT:AVGHE EART PSPT:0.1ccCO CORD IMRT:0.1ccCO CORD 0 Percent

35 Some Observations In the current state of the art, optimality of proton plans is not necessarily superior compared to IMRT plans based on the current criteria (e.g., V20, MLD, etc.) Possible reasons Immaturity of proton therapy technology and techniques IMRT s ability to skirt normal critical structures Greater sensitivity i i of protons to uncertainties i 35

36 However Retrospective results from a prior nonrandomized PSPT NSCLC trial at 74 Gy (RBE) indicate lower lung and esophageal toxicity 36

37 Proton Therapy vs. 3D CRT & IMRT of Locally Advanced NSCLC Median Total Dose 3D CRT & IMRT: 63 Gy Proton therapy: 74 CGE Esophagitis Gr 3 Tx Related Pneumonitis Gr % 40.0% 35.0% 30.0% 25.0% 20.0% 15.0% 10.0% 5.0% 0.0% 35.0% 30.0% 25.0% 20.0% 15.0% 10.0% 0% 5.0% 0.0% 3D IMRT Protons 3D IMRT Protons Proton data form Chang, et al, ASTRO 2009 Abstract 37

38 Possible Explanation Factors other than, or in addition to, V20 and MLD may be responsible for lung toxicity Possibilities include lower heart dose and reduced dose bath for proton therapy Take Home Message There is still a lot to be learned for optimal use of PT 38

39 That is True of All Emerging g Technologies Optimal use of any technology is a moving target 39

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41 Another Perspective There is no such thing as optimum The question that should be asked is: Which technology allows us (or has the potential) ti to achieve the best approximation of our desired d goals 41

42 New Technologies Are new technologies being introduced at too rapid a rate? Are we jumping from one technology to another a before we have had a chance to improve existing technologies and learn how to use it optimally? 42

43 TomoTherapy HI ART System Helical adaptive and imageguided IMRT Planning, image guidance and delivery integrated 43

44 44 Robust Nominal

45 Planning Considerations Relevant dose and dose-volume indices are compared for the first 30 patients enrolled For normal tissue dose distributions ib ti comparisons, each pair of plans is renormalized individually id so that t 95% of the PTV receives the same dose for IMRT and PSPT 45

46 The problem and the solution 46

47 In VMAT, Lateral Gradient May be Sacrificed in Favor of Proximal and Distal Gradient Dose outside the target is a function of the target size 47

48 Lung Normalized DVH Data 80 PSPT IMRT Mean Dose Parameters PSPT IMRT:V IMRT PSPT PT:AVGLUNG IMRT RT:AVGLUNG PSPT: T:AVGHEART IMRT: T:AVGHEART PSPT PT:0.1ccCORD IMRT RT:0.1ccCORD PSPT:V5 IMRT:V5 PSPT:V10 IMRT:V10 PSPT:V20 IMRT:V20 PSPT:V30 IMRT:V30 PSPT:V40 IMRT:V40 PSPT:V50 IMRT:V50 PSPT:V60 IMRT:V60 PSPT:V70 Percent Dose (CGE) PS Heart Normalized DVH Data 80 PSPT IMRT PSP SPT:AVGESO MRT:AVGESO IMR PSPT:V30 IMRT:V30 PSPT:V45 IMRT:V45 PSPT:V60 IMRT:V60 P Pe rcent

49 Prostate Cancer Prostate (min) Proximal SV (min) Rectum (max) Bladder (max) Femoral Heads (max) Solid line: Robust Evaluation of the Plan after Robust Optimization Dash line: Robust Evaluation of the Nominal Plan 49