Large Scale Comparison of In Vitro and Clinical α/β Estimates for Breast, Prostate and H&N Cancer
Abstract
Purpose
To determine, for three common cancers, if in vitro α/β estimates agree with clinical values, and if there are a common pattern of discrepancies.
Methods
A total of 234 clinical and in vitro estimates of α/β for prostate, breast, and head and neck cancer were collected across 108 studies. Statistical tests and correlation analysis were performed to determine a pattern between clinical and experimental values. Bootstrapped Monte Carlo sampling was applied to determine the underlying distribution of α and α/β values, comparing clinical and in vitro distributions. The Poisson TCP model was applied to determine the potential differences between clinical and experimental α and α/β.
Results
Prostate cancer gave median clinical and in vitro estimates of 3.8 Gy and 1.7 Gy respectively. For breast cancer, clinical and in vitro estimates were 3.9 Gy and 3.6 Gy. Head and neck clinical and in vitro were 9 Gy and 14 Gy. Correlation analysis only found a significant correlation with α/β and organ type. TCP curves for in vitro and clinical estimates demonstrated significant differences in the shapes of the curves they generated.
Conclusion
Despite some prominent claims, no evidence was found supporting an agreement between in vitro and in vivo α/β estimates, though both supported α/β estimates either much lower than the commonly applied 10 Gy, or in the case of H&N cancer, at least 10 Gy. Statistically significant differences existed between in vitro and clinical estimates, especially in the estimation of the α parameter. α values tend to be larger for in vitro estimates. Therefore, in vitro estimates of α/β cannot directly predict clinical radiosensitivity estimates.