This document discusses the prostate α/β ratio and the transition to hypofractionation. It covers 1) how hypofractionation could improve therapeutic gain, 2) calculating the α/β ratio, and 3) opposing arguments regarding repopulation times, tumor heterogeneity, and hypoxia. Additional considerations are the acute mucosal reaction of the rectum, using d = 10 Gy, and improvements in IMRT. The conclusions suggest hypofractionation may be suitable for low- and intermediate-risk prostate cancer patients but that more research is needed regarding the impact of hypoxia.

1. Prostate α/β Ratio and Transition
to Hypofractionation
MN Lakshmanan

2. “It is rare that nature hands us a cancer
situation where an improved treatment goes
hand in hand with a shorter and more
convenient one.”
1) Hypofractionation to improve therapeutic gain
2) Calculation of α/β Ratio
3) Opposing Arguments
4) Additional Considerations
J.F. Fowler. Development of radiobiology for oncology - a personal view. Physics in medicine
and biology, 51(13):263, 2006.

3. 1) Hypofractionation to improve
therapeutic gain

4. J.F. Fowler. The radiobiology of prostate cancer including new aspects of fractionated
radiotherapy. Acta Oncologica, 44(3):265-276, 2005.

5. J.F. Fowler. The radiobiology of prostate cancer including new aspects of fractionated
radiotherapy. Acta Oncologica, 44(3):265-276, 2005.

6. Modeling Hypofractionation
J.F. Fowler. The radiobiology of prostate cancer including new aspects of fractionated
radiotherapy. Acta Oncologica, 44(3):265-276, 2005.

7. 2) Calculation of α/β Ratio

8. J. Fowler, R. Chappell, and M. Ritter. Is α/β for prostate tumors really low? International
Journal of Radiation Oncology Biology Physics, 50(4):1021-1031, 2001.

9. J. Fowler, R. Chappell, and M. Ritter. Is α/β for prostate tumors really low? International
Journal of Radiation Oncology Biology Physics, 50(4):1021-1031, 2001.

10. 3) Opposing Arguments
• A) Repopulation times
• B) Tumor Heterogeneity
• C) Hypoxia

11. J.Z. Wang, M. Guerrero, and X.A. Li. How low
is the α/β ratio for prostate cancer?
International journal of radiation oncology,
biology, physics, 55(1):194-203, 2003.
Assumed a fast repopulation time to get
α/β = 3 Gy

12. J.F. Fowler. The radiobiology of prostate cancer including new aspects of fractionated
radiotherapy. Acta Oncologica, 44(3):265-276, 2005.

13. Tumor Heterogeneity
C.R. King and C.S. Mayo. Is the prostate α/β
ratio of 1.5 from Brenner & Hall a modeling
artifact? International Journal of Radiation
Oncology, Biology, Physics, 47(2):536-538,
2000.
Obtained α/β = 5 Gy.

14. A.E. Nahum, B. Movsas, E.M. Horwitz, C.C.
Stobbe, and J.D. Chapman. Incorporating
clinical measurements of hypoxia into tumor
local control modeling of prostate cancer:
implications for the α/β ratio. International
journal of radiation oncology, biology, physics,
57(2):391-401, 2003.

15. 4) Additional Considerations
-acute mucosal reaction of rectum
-d = 10 Gy has been used
-improvements in IMRT

16. Conclusions & Future Work
• Low- & Intermendiate-risk patients
• Hypoxia?