PARENT SESSION
3:45 PM to 5:15 PM
Monday, April 22, 2002
Mini-Symposium 6
Biology, Physics, Chemistry
Room: Nevada 8-9-10
, Co-Chair: Siemann, Dietmar¹; LaVerne, Jay²¹University of Florida, Gainesville, FL²Notre Dame, Notre Dame, IN

(MS06-7) The use of dose responce studies in the determination of the / ratio for prostate cancer.

Carlone, Marco^*,1, Wilkins, David¹, Raaphorst, Peter¹, ¹ Ottawa Regional Cancer Center, Ottawa, Ontario

ABSTRACT-
It has been assumed historically that the / ratio for prostate cancer is similar to that of other cancers. Although the exact mechanisms are not well understood, a general trend has been observed showing that slowly proliferating tissues tend to have a low / ratio in contrast to quickly proliferating tissues where higher / ratios have been measured. It is well documented that prostate cancer proliferates more slowly than most tumors. This observation, combined with some clinical outcomes of prostate cancer hypofractionation have led some investigators to suggest that the / ratio of prostate cancer is somewhat lower than the typical value of 10 Gy associated with most tumors. If this proves to be true, it may have a significant impact upon our approach to the management of the disease. The landmark paper to date is the 1999 publication of Brenner and Hall where the / value of 1.5 Gy was suggested for prostate cancer. King and Mayo, who pointed out that this result is only consistent with an unusually low number of tumor cells, challenged this result in a letter to the editor. Using a model incorporating population variances, King and Mayo proposed / = 4.96 Gy. Our modeling has shown that both these results are in fact partial solutions of a general solution to the problem of fitting radiobiological parameters to clinical dose response studies. This presentation will describe this general solution and we will show how this solution is used to estimate / from dose response studies. We will also show that our more general solution also provides insight into the question of the stability of the / parameter to variation in other radiobiologic parameters.

KEYWORDS: /, prostate, TCP, hypofractionation