Will CyberKnife M6 Multileaf collimator offer advantages over IRIS collimator in prostate SBRT?

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1 Will CyberKnife M6 Multileaf collimator offer advantages over collimator in prostate SBRT? Vindu Kathriarachchi Professional Science Master in Medical Physics Department of Physics, Florida Atlantic University, Boca Raton, FL Lynn Cancer Institute, Boca Raton Regional Hospital, Boca Raton, FL May 1, 2015, Orlando FLAAPM Spring Meeting

2 Purpose To compare dose distributions and time efficiency of SBRT prostate treatments with collimator and InCise of CyberKnife M6 2

3 CyberKnife(CK) Fixed - 12 circular collimators (5 to 60mm). Can select up to three for a treatment dodecagon-shaped collimators (5 to 60mm). Can select all the collimators for the treatment. 1. Echner G.G. et al. Phys Med Biol 54: ; Kilby W. et al. IFMBE proceedings 25: ,

4 CyberKnife(CK) M6 FIM Consists of fixed, variable aperture and InCise Multileaf Collimators. InCise - 41 leaf pairs (max field 10x12cm). Courtesy of Accuray Inc. Courtesy of Accuray Inc. 1. Water S. et al. Int J Radiat Oncol Biol Phys 81:863-70;

5 Prostate SBRT with CK Radiobiology of prostate cancer (low α/β) supports hypo-fractionated treatments. CyberKnife prostate SBRT: 36.25Gy or 35Gy in 5 fractions 1,2. High biochemical control rates: 100% at 30 months 1,2 and 97% at 24 months 3. Low grade rectal and bladder toxicities (similar to conventional EBRT) King C.R. et al. Int J Radiat Oncol Biol Phys 73: ; Katz A.J. et al. BMC Urol 10:1-10; Friedland J.L. et al. Technol Cancer Res Treat 8:387-92;

6 CK Planning Eight prostate cancer patients were planned in MultiPlan using and. Dose Scheme: 36.25Gy in 5 fractions. Prescription isodose: 84-87%. PTV coverage: >95%. : 5 collimators (20, 25, 30, 35 and 40mm). : Non iso-centric with leaf margin 1mm. Structure Type Objective PTV Target 36.25Gy Bladder OAR Max Dose: 38Gy 1 and V 37Gy < 10cc 2 Rectum OAR Max Dose: 38Gy 1 and V 36Gy < 1cc 2 1. Timmerman R.D. Semin Radiat Oncol 18(4):215 22; Friedland J.L. et al Technol Cancer Res Treat 8:387-92;

7 Dosimetric Comparison of vs PTV coverage Baldder Wall D max and Rectum D max. Baldder Wall V 37Gy and Rectum V 36Gy 1. Conformity index (CI): CI = PV TV PV New conformity index (nci) 2 : nci = PV.TV TV PV 2 Gradient index (GI): GI = Vp 2 % V p% 1. Friedland J.L. et al Technol Cancer Res Treat 8:387-92; Paddick I. J Neurosurg 93:219 22;

8 Radiobiological Comparison Equivalent uniform dose (EUD) 1 : EUD = i=1 a v i D i 1 a Normal tissue complication probability (NTCP): NTCP = TD 50 EUD 4γ 50 Tumor control probability (TCP): TCP = Structure a α/β(gy) TD 50 (Gy) γ 50 TCD 50 (Gy) TCD 50 EUD 4γ 50 Prostate Bladder Rectum Niemierko A. Med Phys 26:1100; Gay H. and Niemierko A. Phys Med 23:115-25; Rana S. and Cheng C.Y. Ann Med Health Sci Res 4: ;

9 Dose Distribution Bladder Wall PTV Rectum 9

10 PTV Coverage, CI and nci nci CI PTV Coverage (%) p PTV 95.54% 95.61% CI nci PTV coverage, CI and nci are not significantly different (Wilcoxon signed-rank test) 10

11 Bladder Wall - V 37Gy (cc) Rectum - V 36Gy (cc) Dmax_Bladder Wall (cgy) Dmax_Rectum (cgy) Bladder Wall and Rectum

12 Comparison Bladder Wall and Rectum p Bladder Wall Max Dose (cgy) Bladder Wall V 37Gy (cc) Rectum Max Dose (cgy) Rectum V 36Gy (cc) Bladder wall and Rectum doses are not significantly different (Wilcoxon signed-rank test). 12

13 Gradient Index Total MUs Treatment Time (mins) Total MUs, Treatment time, and Gradient Index 7x x x x x x % Diff p MUs % TT (mins) % GI %

14 Tumor EUD (Gy) TCP(%) Tumor EUD and TCP p EUD (Gy) TCP (%)

15 NTCP Bladder Wall (%) NTCP Rectum (%) NTCP (Bladder Wall and Rectum) 1.2E E E E E E E E+00 NTCP for both, Bladder wall and Rectum are <1%. 15

16 Conclusion InCise of CyberKnife M6 and can both produce equivalent prostate treatment in terms of target coverage, critical structure sparing, TCP and NTCP. Yes, InCise of CyberKnife M6 offers a significant reduction in treatment time (36%) and total MUs (42%) compared to. 16

17 Future Work Compare dose distributions and time efficiency of prostate SBRT treatments with conventional linac and Cyberknife M6. Compare dose distributions and time efficiency of lung SBRT treatments with collimator and InCise. 17

18 Collaborators Charles Shang, MS DABR Georgios Kalantzis, Ph.D Theodora Leventouri, Ph.D Grant Evans, MS 18

19 Acknowledgements Lynn Cancer Institute, Boca Raton Regional Hospital, for making their facilities and personnel available. Department of Physics, Florida Atlantic University, for financial support. 19

20 Thank you!