The delta-TCP concept: a clinically useful measure of tumor control probability.
OBJECTIVE
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
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.


CONCLUSIONS
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.
Sanchez-Nieto
B
B
Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Trust, Sutton, United Kingdom. beatriz@icr.ac.uk
Nahum
A E
AE
D000465:Algorithms; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D016014:Linear Models; D008297:Male; D015233:Models, Statistical; D009369:Neoplasms / Q000532:radiotherapy*; D016012:Poisson Distribution; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D011853:Radiobiology