Dosimetric Effects of Using Generalized Equivalent Uniform Dose (geud) in Plan Optimization Ontida Apinorasethkul, MS, CMD AAMD Indianapolis June 14, 2017
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
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
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
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
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
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
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
α values TG-166 report 9
α values Quantec / Burman 1 0
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
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
α values Different alpha values Same priority value 1 3
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
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
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
DV-based optimization objectives 1 7
geud based optimization objectives 1 8
Plan comparisons 1 9
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 40 2 0
Prostate plan DV-based objectives geud-based objectives 2 1
Prostate plan DV geud 2 2
Prostate plan DV geud 2 3
Prostate plan DV geud 2 4
Prostate plan Mean dose (cgy) DV geud Bladder 2070 1781 Rectum 2515 2503 2 5
Prostate plan Mean dose (cgy) DV geud Femoral head_l 1233 870 Femoral head_r 1318 895 2 6
Pelvis plan DV-based objectives 2 7
Pelvis plan geud-based objectives 2 8
Pelvis plan DV geud 2 9
Pelvis plan DV geud 3 0
Pelvis plan DV geud Dose max 109.5% Dose max 116.2% 3 1
Pelvis plan Mean dose (cgy) DV geud Small bowel 1710 1460 Large bowel 3087 2637 Rectum 3091 2967 Bladder 3715 3465 3 2
Brain plan DV-based objectives 3 3
Brain plan geud-based objectives 3 4
Brain plan DV geud 3 5
Brain plan DV geud 3 6
Brain plan DV geud 3 7
Brain plan DV geud 3 8
Brain plan Organs DV geud Brainstem (max) 5753 5264 Temporal lobe_l (mean) 2882 2600 3 9
H&N plan DV-based objectives 4 0
H&N plan geud-based objectives 4 1
H&N plan DV geud 4 2
H&N plan DV geud 4 3
H&N plan DV geud 4 4
H&N plan DV geud 4 5
H&N plan DV geud 4 6
H&N plan Max dose (cgy) DV geud Brainstem 3526 2832 Cord 4074 2182 Cord+5mm 4623 2757 4 7
H&N plan Mean dose (cgy) DV geud Oral cavity 1261 1340 Larynx 2223 2511 Constrictor 3271 2952 4 8
H&N plan Mean dose (cgy) DV geud Submandibular_L 3145 2928 Parotid_L 2871 2642 Parotid_R 1620 1503 4 9
Lung plan DV-based objectives geud-based objectives 5 0
Lung plan DV geud 5 1
Lung plan DV geud 5 2
Lung plan DV geud 5 3
Lung plan DV geud 5 4
Lung plan DV geud 5 5
Lung plan IMRT same fields Max dose (cgy) DV geud Brachial plexus_r 4419 3695 Cord 3608 1407 Cord+5mm 3977 2083 5 6
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
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
Acknowledgements Derek Dolney, PhD Akhil Tiwari, CMD Dimitris Mihailidis, PhD 5 9
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