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A variable critical‐volume model for normal tissue complication probability
Author(s) -
Bonta Dacian V.,
Fontenla Ernesto,
Lu Yong,
Chen George T. Y.
Publication year - 2001
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1380432
Subject(s) - variable (mathematics) , volume (thermodynamics) , medical imaging , mathematics , statistics , medicine , radiology , physics , mathematical analysis , quantum mechanics
Predicting late‐term normal‐tissue complication probability (NTCP) after radiotherapy is an important factor in the optimization of conformal radiotherapy. We propose a new NTCP model, based on the properties of the high dose region. The principal assumption of the new model is that a whole‐organ complication will occur when the radiation damage to a normal organ volume (a portion of the total organ) exceeds a threshold value. The dose threshold for complications varies with the size of the volume (percent of the total organ). We hypothesize that a complication occurs if the complication threshold is exceeded for any organ volume. We used the average dose to a volume as a measure of radiation damage to that volume. Also, we used the power law to scale the average dose to various organ volumes to a whole‐organ equivalent dose, and to identify the volume with the most harmful dose‐size combination—the critical volume. We used a logistic distribution to calculate the probability that the patient will develop a complication, given the dose delivered to the critical volume. We used a maximum likelihood fit to estimate the model parameters for late‐term rectal complications in a set of patients treated for prostate carcinoma with external photon beam radiotherapy (EBRT). Good correspondence was found between the experimental data and the model predictions.