Future directions and current challenges of proton therapy

1. Future directions and current challenges of proton therapy Planning CT CT after 5 weeks Tony Lomax, Centre for Proton Radiotherapy, Paul Scherrer Institute, Switzerland

2. Overview of presentation • State-of-the-art proton delivery • Current challenges • New directions in proton therapy • Summary

3. State-of-the-art proton delivery Compensator Collimator Scatterer Range-shifter wheel Target Patient Passive scattering

4. State-of-the-art proton delivery Magnetic scanner ‘Range shifter’ plate Spot scanning Proton pencil beam Target Patient Pedroni et al, Med Phys. 22:37-53, 1995

5. State-of-the-art proton delivery Intensity Modulated Proton Therapy (IMPT) Fully automated delivery (scanning) The present and future of proton therapy? Passive scattering (patched fields) Collimators and compensators required for each field

6. State-of-the-art proton delivery 9 field IMRT plan Factor 6 lower integral dose for protons Sarcoma – 12 year old boy Delivered single field plan

7. State-of-the-art proton delivery Integral dose and secondary cancer risk N Tarbell, ASTRO, 2008 Study comparing 503 proton patients to 1591 photon patients (treated 1974-2001) showed a 50% reduction in secondary tumours in proton patients K Haeller, PSI

8. Overview of presentation • State-of-the-art proton delivery • Current challenges • New directions in proton therapy • Summary

9. Current challenges: range uncertainty The disadvantage of protons is that we don’t always know where… 10% range error Range uncertainty The advantage of protons is that they stop.

10. Current challenges: range uncertainty Initial Planning CTGTV 115 cc 5 weeks later GTV 39 cc Tumour shrinkage S. Mori, G. Chen, MGH, Boston

11. Current challenges: range uncertainty Tumour shrinkage Planning CT CT after 5 weeks Beam overshoot Beam stops at distal edge S. Mori, G. Chen, MGH, Boston

12. Current challenges: range uncertainty During treatment, 1.5kg weight gain was observed New CT Planning CT Max range differences: SC 0.8cm CTV 1.5cm Patient weight changes 3 field IMPT plan to an 8 year old boy Note, sparing of spinal cord in middle of PTV Francesca Albertini and Alessandra Bolsi (PSI)

13. Current challenges: range uncertainty Many patients referred for RT post-operatively and with metal (titanium) stabilisation How accurately can we calculate proton ranges in such CT data sets? CT artefacts

14. Current challenges: range uncertainty Without implant (n = 13) 3-yr, 5-yr 100% 1 .8 3-yr 69% 5-yr 46% .6 Implants (n =13) .4 .2 0 0 10 20 30 40 50 60 Months Chordomas and chondrosarcomas of the spinal axis Rutz et al 2007, IJROBP, 67, 512-520

15. Current challenges: organ motion What is the effect of organ motion on proton therapy? Organ motion 4D-CT derived from 4D-MRI Martin von Siebenthal, Phillipe Cattin, Gabor Szekely, Tony Lomax, ETH, Zurich and PSI, Villigen

16. Current challenges: organ motion Organ motion and passive scattering Parallel opposed photons Single field protons Single field photons Images courtesy of Thomas Bortfeld, MGH, Boston

17. Current challenges: organ motion Organ motion and passive scattering Parallel opposed photons Single field protons Single field photons Images courtesy of Thomas Bortfeld, MGH, Boston

18. Current challenges: organ motion Organ motion and scanning A scanned beam in a moving patient. 4D-CT derived from 4D-MRI Martin von Siebenthal, Phillipe Cattin, Gabor Szekely, Tony Lomax, ETH, Zurich and PSI, Villigen

19. Current challenges: organ motion Calculated with ‘real’ motion from 4D-MRI of volunteer Organ motion and the ‘interplay’ effect Nominal (static) dose

20. Current challenges: organ motion 100 100 80 80 60 60 Volume (%) Volume (%) 40 40 20 20 0 0 70 70 80 80 90 90 100 100 110 110 120 120 Dose (%) Dose (%) Organ motion and the ‘interplay’ effect Motion patient 2 Amplitude ~ 8mm Motion patient 1 Amplitude ~ 11mm Scanning is particularly sensitive to organ motion

21. Current challenges: treatment gantries Adenoid cystic carcinoma with node involvement Tricky to do without a gantry…

22. Current challenges: treatment gantries Avoiding density heterogeneities Each point is a different field calculated for the same skull base case A comparison of MC and analytical dose calculations as a function of density heterogeneities Heterogeneity index

23. Current challenges: treatment gantries Avoiding density heterogeneities

24. Current challenges: treatment gantries 7m diameter 3.5m diameter PSI gantry 2 PSI gantry 1 15m diameter 12m diameter Loma Linda Heidelberg Could this be the main limit to the spread of particle therapy?

25. Overview of presentation • State-of-the-art proton delivery • Current challenges • New directions in proton therapy • Summary

26. New directions in proton therapy • Possible improvements to passive scattering • Dealing with range uncertainties • Organ motion and scanning

27. New directions in proton therapy • Dealing with range uncertainties • Organ motion and scanning • Gantry design

28. Dealing with range uncertainties Proton radiography Activation PET Measured PET activation Proton radiograph Calculated PET activation Proton DRR Katia Parodi, Thomas Bortfeld MGH, Boston Uwe Schneider, Zurich Alexander Tourovsky, PSI Imaging for range MV-CT kV-CT MV-CT (Hi-Art) Ospedale San Rafaele, Milan Francesca Albertini, PSI

29. Dealing with range uncertainties Nominal plan Robust planning techniques Example paraspinal case Tumour Spinal cord 10% overshoot Lomax et al.:Med. Phys. 28(3): 317-324, 2001

30. Dealing with range uncertainties ...give a homogenous dose without the use of fields that abut distally against the spinal cord Robust planning techniques 3 patched, intensity modulated fields.... Lomax et al.:Med. Phys. 28(3): 317-324, 2001

31. Dealing with range uncertainties Nominal plans 10% overshoot plans DVH analysis IMPT IMPT Spinal cord Dtol Relative volume Single field Single field Relative dose Nominal Single field Overshoot Nominal IMPT plan Overshoot Robust planning techniques

32. Dealing with range uncertainties Range adapted proton therapy Alessandra Bolsi, PSI

33. Dealing with range uncertainties Work of Alessandra Bolsi. Range adapted proton therapy Alessandra Bolsi, PSI

34. Dealing with range uncertainties Range adapted proton therapy Alessandra Bolsi, PSI

35. Dealing with range uncertainties Range adapted proton therapy Alessandra Bolsi, PSI

36. New directions in proton therapy • Dealing with range uncertainties • Organ motion and scanning • Gantry design

37. Organ motion and scanning Rescanning Repaint scanned beam many times such that statistics dictate coverage and homogeneity of dose in target (c.f. fractionation)

38. Organ motion and scanning Rescanning Re-scanning in presence of Cos4 motion with 1cm amplitude • Cylindrical target volume • Re-scanned different times to same total dose • Scan times calculated for realistic beam intensities and dead times between spots • Analysis carried out for different periods of motion 4s period Not always improving homogeneity with number of re-scans! Marco Schwarz, Silvan Zenklusen ATREP and PSI

39. Organ motion and scanning Rescanning The ‘synchronicity’ effect • Very preliminary results • A ‘real’ effect for perfectly regular breathing? • Could well be less of an issue when breathing is more irregular • For regular breathing, could be avoided by selecting the re-scanning period to avoid effect or varying period scan-to-scan • Probably not a big issue in reality See presentation from Silvan Zenklusen, Saturday

40. Organ motion and scanning Tracking Track motion of tumour using scanning system based on some anatomical/physiological signal

41. Organ motion and scanning Vedam et al 2004 ~150ms delay Tumour Tracking Plot of dose homogeneity as function of RMS position error due to motion and ‘imperfect’ tracking Cos4 motion with varying detection delays and tracking accuracies Steven van de Water, PSI/TUDelft

42. Organ motion and scanning Vedam et al 2004 ~150ms delay Tumour Tracking Re-tracking – tracking the tumour repeatedly within one fraction E.g. 4 times Steven van de Water, PSI/TUDelft

43. New directions in proton therapy • Dealing with range uncertainties • Organ motion and scanning • Gantry design

44. Gantry design Still rivers systems single room proton facility To stay competitive with other therapies for the next 25 years, treatment gantries will almost certainly be necessary DWA based proton tomotherapy Probably the biggest step forward for particle therapy would come from a significant reduction in gantry size

45. Summary • Although passive scattering is still the preferred choice for proton therapy, scanning and IMPT will become more widespread in the next years (c.f. MD Anderson) • To what extent can scattering be improved through the use of automated field hardware (MLC’s etc)? • Range uncertainty and organ motion (particularly for scanning) remain the main challenges to proton therapy and much interesting and exciting work is still to be done in organ management, range imaging and adaptive proton therapy • The field is ripe for new input, ideas and innovations…