Dosimetric Effects of Using Generalized Equivalent Uniform Dose (geud) in Plan Optimization

Transcription

1 Dosimetric Effects of Using Generalized Equivalent Uniform Dose (geud) in Plan Optimization Ontida Apinorasethkul, MS, CMD AAMD Indianapolis June 14, 2017

2 Disclaimer This presentation is not sponsored by any vendor nor is it endorsing one treatment planning system over another. The material presented is based on our planning experience. This talk is meant for educational purposes. 2

3 Overview What is geud? α values geud optimization Benefits and drawbacks Plan comparisons against dose volume- (DV) based objectives Prostate Whole pelvis Brain H&N Lung 3

4 What is geud? Generalized Equivalent Uniform Dose The dose that, if given uniformly to the entire organ, is believed to yield the same complication rate as the true dose distribution (QUANTEC) Accommodates the concept of serial and parallel organs Achieve same tumor response, lower normal tissue dose More non-uniform dose distribution Less dependent on the variability of patient s shapes and sizes Less trial and error when planning one case to another 4

5 What is geud? Eclipse 13.5 and newer New photon optimizer (PO) algorithm Supports biological optimization objectives Implement biological planning in daily treatment planning DV = biological response geud = estimates of the biological outcome IMRT and RA optimization Shift to a non-uniform target dose distribution? Organ motion Daily set up uncertainties Brachytherapy SRS/SBRT Simultaneous integrated boost 5

6 Workout analogy Goal: lose 5 pounds in 2 months Cardio only Weight training only Combinations? End result: Weight loss is equivalent to 5 pounds 6

7 geud optimization For tumors, the EUD represents the biologically equivalent dose which, if given uniformly, leads to the same cell kill in the tumor volume as the actual non-uniform IMRT dose-distribution. EUD = TG-166 7

8 α values geud is dependent on α value. Tissue-specific parameter that describes the volume effect of geud Defines where on the DVH the optimization is to be focused on Values range from -40 to +40, but can never be zero -40 to -1 = tumor range 1 = mean objective 1 to 40 = organs at risk range Low α values: parallel organs High α values: serial organs 8

9 α values TG-166 report 9

10 α values Quantec / Burman 1 0

11 geud optimization Target geud α of -40 to -1 Defines an exact Equivalent Uniform dose value Ex: PTV must receive 95% of dose. Similar to lower objective of DVbased optimization Lower geud α of -40 to -1 Defines the minimum Equivalent Uniform dose value Ex: PTV must receive at least 60 Gy. Works well on overlapping structures Varian 1 1

12 geud optimization Upper geud α of 40 to 1 Defines the maximum Equivalent Uniform Dose value Ex: Inner ear may receive no more than 25 Gy. Lower α value in the upper geud will affect majority of the DVH curve Higher α value in the upper geud will affect max dose of the DVH curve Varian 1 2

13 α values Different alpha values Same priority value 1 3

14 Benefits and drawbacks Typically lower normal tissue dose while maintaining tumor coverage geud objectives are generally used for organs at risk Instead of several upper objectives on multiple contours Smaller number of parameters used, larger space of solutions become available Less ambiguity in less number of objectives Limit max dose Lower mean dose Limited number of parameters controlled by user Details of dose distribution can t be fine tuned 1 4

15 geud optimization With our experience.. Using only geud objectives on target volumes could result in a highly non-uniform dose distribution Avoid target dose heterogeneities that would not be accepted in clinical plans Evaluate plans for non-uniform dose 1 5

16 geud optimization With our experience.. Use upper and lower objectives of DV-based optimization for a better control over target dose distribution geud works better on normal tissue optimizations 1 6

17 DV-based optimization objectives 1 7

18 geud based optimization objectives 1 8

19 Plan comparisons 1 9

20 Plan comparisons Research phase Same field parameters Arcs / collimator angles Field gantry DV-based optimization Multiple upper objectives on organs at risk Optimize on crop structures geud-based optimization PTV objectives - same as DV-based optimized plan Optimize on whole organs at risk structure One upper geud objective for each structure* α of 1, 20, or

21 Prostate plan DV-based objectives geud-based objectives 2 1

22 Prostate plan DV geud 2 2

23 Prostate plan DV geud 2 3

24 Prostate plan DV geud 2 4

25 Prostate plan Mean dose (cgy) DV geud Bladder Rectum

26 Prostate plan Mean dose (cgy) DV geud Femoral head_l Femoral head_r

27 Pelvis plan DV-based objectives 2 7

28 Pelvis plan geud-based objectives 2 8

29 Pelvis plan DV geud 2 9

30 Pelvis plan DV geud 3 0

31 Pelvis plan DV geud Dose max 109.5% Dose max 116.2% 3 1

32 Pelvis plan Mean dose (cgy) DV geud Small bowel Large bowel Rectum Bladder

33 Brain plan DV-based objectives 3 3

34 Brain plan geud-based objectives 3 4

35 Brain plan DV geud 3 5

36 Brain plan DV geud 3 6

37 Brain plan DV geud 3 7

38 Brain plan DV geud 3 8

39 Brain plan Organs DV geud Brainstem (max) Temporal lobe_l (mean)

40 H&N plan DV-based objectives 4 0

41 H&N plan geud-based objectives 4 1

42 H&N plan DV geud 4 2

43 H&N plan DV geud 4 3

44 H&N plan DV geud 4 4

45 H&N plan DV geud 4 5

46 H&N plan DV geud 4 6

47 H&N plan Max dose (cgy) DV geud Brainstem Cord Cord+5mm

48 H&N plan Mean dose (cgy) DV geud Oral cavity Larynx Constrictor

49 H&N plan Mean dose (cgy) DV geud Submandibular_L Parotid_L Parotid_R

50 Lung plan DV-based objectives geud-based objectives 5 0

51 Lung plan DV geud 5 1

52 Lung plan DV geud 5 2

53 Lung plan DV geud 5 3

54 Lung plan DV geud 5 4

55 Lung plan DV geud 5 5

56 Lung plan IMRT same fields Max dose (cgy) DV geud Brachial plexus_r Cord Cord+5mm

57 Summary With one iteration of optimization, geud optimized plan generally shows lower dose to organs at risk Fine tuning is still needed Higher global max In general, geud based optimization can help improve normal tissue sparing while maintaining the same or better target volume coverage 5 7

58 Summary Use radiobiological based model tools/algorithms to our benefits with caution Results in non-uniform target dose No one method is perfect More research needed of new function Use of geud on target volumes in the future 5 8

59 Acknowledgements Derek Dolney, PhD Akhil Tiwari, CMD Dimitris Mihailidis, PhD 5 9

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