# TDF Plan: Normal Tissue Complication Probability

NTCP calculations are available in TDFPlan versions 1.4.3 and greater. To calculate NTCP, click the Normal Tissue Tolerance... button located in the IMR group of the TDF Plan main window.

This will open the Normal Tissue Tolerance (NTT) dialog window illustrated below.

In the NTT list, click on the row corresponding to the tissue of interest (TOI) and the column of the volume of interest (VOI). In this example the 5%/5yr tolerance for Whole Colon has been selected. You can display the tolerance doses as absolute total dose (cGy) or as biologically effective dose (BED Gyα/β) using the checkbox at the top of the list. In this example the tolerance doses are expressed as BED to be fractionation independent. The tolerance dose data in the default file TDFTolerance.txt located in the TDFData folder provides a good fit when NTCP is plotted as a function of BED and assuming the fraction size was 200 cGy. You can explore the behavior of the NTCP model by playing with the fit paramters using the text fields and arrow bumpers and save the modified results if you wish. The name of the default tolerance file loaded at startup can be changed in the preferences section. To plot NTCP as a function of dose (Gy) or BED (Gyα/β) click the Graphs button. In the plot on the right NTCP for whole colon is plotted as a function of BED assuming an α/β of 4.0 Gy and α = 0.0981 Gy-1. The square symbols represent the 5% and 50% 5 year data points for whole colon (largest), 2/3 volume (medium) and 1/3 volume (smallest) from the table assuming that the tolerance doses were delivered using the NTT dose/fraction (e.g. 200 cGy/fraction in this example). The plotted curve is constrained to pass through the currently selected VOI for the TOI (e.g. the 5%/5yr tolerance of 4500 cGy (BED = 68.01 Gy4.0) in this case). NTCP calculations for the currently selected course regimen (e.g. course #1, 6000 cGy delivered as 30 fractions of 200 cGy) is tabulated in the NTCP table and explanation at the lower left of the NTT window. |

Below are some similar screen captures from the windows version of TDF Plan for a different course and using a different assumption for the NTT dose/fraction of 180 cGy.

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