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The delta-TCP concept: a clinically useful measure of tumor control probability
1Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Trust, Sutton, United Kingdom. beatriz@icr.ac.uk
Purpose:
The aim of this article is to provide a quantitative tool to evaluate the influence of the different dose regions in a non-uniformly irradiated tumour upon the probability of controlling that tumor.
Methods And Materials:
First, a method to generate a distribution of the probability of controlling the cells in a voxel (VCP) is explored and found not to be useful. Second, we introduce the concept of delta-TCP, which represents the gain or loss in the overall TCP as a result of each particular bin in a DVH not receiving the prescribed dose (the same concept is applicable to dose cubes or to a fraction of the bin). The delta-TCP method presented here is based on the Poisson TCP model, but any other model could also be used. Third, using this tool, with parameters appropriate to Stage C prostate tumors, the consequences of "cold" and "hot" dose regions have been explored.
Results:
We show that TCP is affected by the minimum dose, even if it is delivered to a very small volume (20% dose deficit to 5% of the volume makes the TCP decrease by 18%), and that a hot region may be "wasted" unless the boost is to the bulk of the volume. An example of the application of the delta-TCP concept to a prostate radiotherapy plan is also given.
Conclusion:
The delta-TCP distribution adds more objective information to the original DVH by enabling the clinician or planner to directly evaluate the effects of a non-uniform dose distribution on local control.