1. 1 Improved critical structure sparing with biologically based IMRT optimization X.Sharon Qi, Vladimir A. Semenenko and X. Allen Li Department of Radiation Oncology, Medical College of Wisconsin

2. Introduction  DVH based algorithm ignore the nonlinear dose response of both tumor and normal structure  Dose-based optimization is insufficient to predict any biological end point of radiotherapy  Biologically based radiation treatment planning can substantially improve the quality of the plan generated

3. Purpose Ø to study the impact of using biological models on plan quality by evaluating commercially available treatment planning systems Ø

4. Methods and materials Ø Ø Ø Ø

5. A. TPS ØTPS: CMS (Monaco, XiO) Ø Philips Pinnacle Ø Ø Tomotherapy

6. Ø Biological objective functions in TPS

7. ØPhysical objective functions

8. B. Study design  Five clinical cases: brain, H&N, lung, pancreas and prostate  The original treatment plans were generated by using XiO or Tomotherapy  Two physically based IMRT(pIMRT) and two biologically based (bIMRT) plans were generated for each cases utilizing different TPSs  Same planning CT and structure set  Same beam numbers and orientations

9. ØFix angles: Ø pIMRT: XiO (XiO) Ø pIMRT: Pinnacle (Pinn_phy) Ø bIMRT: Monaco (Monaco) Ø bIMRT: Pinnacle (Pinn_bio) ØRotation: Ø Tomotherapy (Tomo)

10. C. Plan comparison (pIMRT vs. bIMRT) ØDVH ØHeterogeneity index (HI): the ratio of the minimum dose delivered to the hottest 5% of the PTV to the minimum dose delivered to the hottest 95% of the PTV ØConformity index (CI): the ratio of volume inside the isodose surface corresponding to the prescription dose compared to the volume of the target ØOverall plan ranking index (fEUD)

11. EUD ØThe uniform dose that gives the same biological effect as a given nonuniform dose distribution Øa: the tumor or normal tissue specific parameter Ø a=1/n for the relationship of Lyman model Ø Malignant tumor targets general have large negative values Øserial-type organ has a large positive value (penalize hot spots) Øparallel structure organ use a small positive value

12. fEUD: EUD-based figure-of-merit Weighting factors, correspond to the complication probability (for ith OAR) and/or control probability for jth target The relative importance factor between the weighted sums of EUDs for all targets and OARs

13. Results ØA. Dose distributions and DVHs

14. Head and Neck case in target: Similar target coverage

15. Head and Neck case: DVH of OARs

16. Prostate case

18. Comparison of the dose ranges from the minimum to maximum doses and the mean doses for the five cases(1)

19. Comparison of the dose ranges from the minimum to maximum doses and the mean doses for the five cases(2)

20. ØbIMRT plans offer improved OAR sparing ØThe target coverage for both pIMRT and bIMRT plans are comparable; Tomo plans are slightly more uniform ØMonaco plans show slightly more heterogeneous dose distributions in targets compared with other plans

21. B. Dose conformity and hetergenetiy Monaco plans and Pinn_bio plans: more conformal Monaco: similar or higher HI Pinn_phy and Pinn_bio: similar HI Tomo: similar or lower values of CI and HI

22. C: The equivalent uniform dose

23. ØAll five plans give similar EUDs ØMonaco plan results in slightly greater EUDs values in 11 out of 12 targets in all five cases ØCompared to Pinn_phy plans, Pinn_bio plans lead to 7 out of 12 targets receiving higher EUDs, while 32 out of 37 OARs receive lower EUDs ØThe Monaco and Pinn_bio plans yield similar OAR sparing

24. D. Overall plan figure-of-merit(fEUD)

25. E. DVH dependence of parameter a cordRight parotid

26. Conclusion ØThe use of biological models in treatment planning optimization can generate IMRT plans with significantly improved normal tissue sparing with similar or slightly increased dose heterogeneity in target ØCaution should be exercised in choosing appropriate models and/or model parameters and in evaluating the plan obtained when using the biologically based treatment planning system

27. Thank you!