1. The 4 Rs Repair Redistribution Repopulation Reoxygenation

2. Direct vs. indirect effect of radiation

3. Indirect action

5. Oxygen stabilizes free radicals

6. … so they can travel farther

7. More oxygen  more cell killing with the same dose

8. OER (Oxygen Enhancement Ratio) OER = Dose required to cause effect with oxygen Dose required to cause effect without oxygen

9. A very big effect tipically: OER = 2.5-3

11. Two false statements: 1.High LET radiation is insensitive to hypoxia 2.Carbon ion RT is high LET radiation

13. OER is not 1 for 74 KeV/micron carbon !

14. Hypoxia Normal tissue pO2 40 – 60 mmHg pO2 < 10 mmHg hypoxia pO2 < 3 mmHg severe Tatum et al., (2006)'Hypoxia: Importance in tumor biology, noninvasive measurement by imaging, and value of its measurement in the management of cancer therapy', International Journal of Radiation Biology,82:10,699 — 757

15. Human cancers are hypoxic

16. Only very smal tumors are not hypoxic

17. Hypoxia is an interesting subject Fyles et al. JCO 2003 Cervical cancer survival dependso on tumor hypoxia (polarographic Eppendorf needle electrode measurments)

18. Two favourable characteristics 1.Hypoxia is a microenvironment property (not a single cell one) 2.Hypoxia can be measured

19. Microenvironment

21. Measuring hypoxia polarographic needle electrodes PET

22. 18F-MISO First reduction only inside living cells, if pO2> 20 mmHg there is a immediate re-oxidation, otherwise there is a second reduction and the drug can bind to nmacromolecules and accumulate within the cell Easy to produce and ship

23. Sub-optimal contrast

24. Cu-ATSM First reduction only inside living cells (NADH is needed ) Second reduction only if low pO2 Good contrast Radioactive Cu is more difficult to produce: Cu60 half life 24 min

25. Better contrast with Cu-ATSM

26. Hypoxia measured with Cu-ATSM PET is still predictive of survival in cervical cancer

27. Hypoxia measured with F-miso PET is predictive of outcome in head and neck cancer

28. Static or kinetic PET measurements?

30. TAC (Time Activity Curves) are created One F-miso injection, multiple data acquisition over time

32. Three patterns Well perfused no hypoxia Well perfused diffusion /demand limited hypoxia Structural hypoxia

35. Scatter plots W 0 describes how fast the radiodrug goes from the blood to the interstitial fluid W a k 3 describes how fast it is trapped in hypoxic cells

36. a)hypoxic because of poor blood supply b)Hypoxic despite good blood supply (increased consumption ?) c)Well oxygenated Three kinds of tumors:

38. Can we make good use of these information ? More treatment for hypoxic tumors: – Radiosensitizers (Tirapazamine phase II TRACE closed for excess deaths)  maybe not a good idea – Dose escalation ? – Carbon ions ?

39. Dose escalation for hypoxic tumors More dose to the tumor (uniform dose escalation) More dose to the hypoxic tumor (dose painting by contours DPBC) The more it is hypoxic the higher the dose (Dose Painting By Numbers DPBN)

40. Uniform dose escalation Hypoxia information is used only to decide weather or not to give an additional 6 Gy (70  76) the volume is decided indipendently (e.g. FDG - PET)

41. Dose painting by contours (1) All the volume with drug uptake (Cu-ATSM) over a threshold receives the boost (80 Gy vs. 70 Gy)

42. Dose painting by numbers More drug (F-Miso) more hypoxia more dose

43. Hipoxic volume change (by itself) Lin et al. IJROBP 2008

44. Hypoxic volume changes, thanks to RT It would be desiderable to describe the change of hypoxia and possibly the influence of RT on reoxygenation. Multiple PET over the RT treatment duration would be necessary

45. Only 15 HN patients, serial F-Miso (dynamic) PET: at least at 0 and 20 Gy, for some patients also at 50 Gy and 70 Gy

46. 0 Gy 20 Gy 50 Gy How do perfusion and retention change during therapy ? (according to Thorwarth model) reoxigenation Inflammation ?

47. What is the effect of reoxygenation ? Tumor control probability Cancer (stem) cell density in voxel i Sum over all teh voxels Radiosensitivity in voxel i Dose in voxel i

48. To describe hypoxia and reoxigenation: At the beginning radiosensitivity is lower and depends from distance to vessel, after a time tr re-oxygenation takes place

49. Two assumptions are made by the authors: 1 radiosensitivity is directly proportional to F- miso retention 2 time to reoxygenation is inversely proportional to perfusion

50. Acceptable fit of clinical data strenghtens those assumptions

51. What is the mechanism of reoxygenation ? Reduced consumption od stunned tumor cells Increased perfusion due to inflammation Tumor shrinkage fast slow

52. Unpublished data seem to show that a much stronger predictor of poor outcome as compared to hypoxia is failure ot reoxygenate Dose escaltion at its best should be given in a clever way (time and space) Space  the volume that does not re- oxigenate (DPBN or DPBC) Time  sooner or later ?

53. Sooner or later ?

54. How much dose escalation ? Arbitrary : 70 Gy  80 Gy Based on TCP model : M being the excess number of live cell in a voxel due to hypoxia

55. Sooner or later ? Appling dose escalation after the re- oxygenation has taken place might be more efficient as you do not ‘waste’ precious extra dose in the initial phase when the hypoxic cells would not be damaged ?

56. Conclusions Hypoxia and re-oxygenation are important They are complex but can be measured Dynamic and repeated PET give a lot of information These information can be analyzed quantitatively and these process can be modellized

57. Conclusions Groundbreaking work has been done on modellization (but of course clinical confirmation must still be obtained) If the models are valited they can be used to drive dose escalation in a rational way telling us what to boost, when to boost and how much to boost

58. Conclusions Hypoxia and reoxygenation are relevant also for carbon ion radiotherapy Presented methodology could be applied also in hadrontherapy in clinical setting and could give informations on real ability of carbon ion to overcome hypoxia and on optimal combination of carbon and x-ray

59. Is time to reoxygenation indepenent from dose ?

60. Reality is a complex thing ’Hypoxia promotes adaptive processes that lead to tumor aggressiveness, progression, and acquired resistance to treatment … Changes dependent on hypoxia inducible factors (HIF) trigger metabolic adaptation, improved systemic oxygen supply, cell survival, and cell proliferation. Changes independent of HIF promote resistance to apoptosis and uppression of anticancer immune response. Tumors with pO2 values less than 1 mm Hg exhibit genomic changes such as point mutations, chromosomal aberrations, gene amplification, and polyploidy. Genetic instability results in the emergence of new genetic variants that can survive under otherwise lethal conditions, leading to a Darwinian selection process of the most resistant clones’