A variable critical-volume model for normal tissue complication probability.
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.
Bonta
D V
DV
Department of Radiation and Cellular Oncology, University of Chicago, Illinois 60637, USA. d-bonta@uchicago.edu
Fontenla
E
E
Lu
Y
Y
Chen
G T
GT
D000465:Algorithms; D006801:Humans; D016013:Likelihood Functions; D016015:Logistic Models; D008297:Male; D015233:Models, Statistical; D017785:Photons; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D020266:Radiotherapy, Conformal / Q000009:adverse effects* / Q000379:methods*