In:
Medical Physics, Wiley, Vol. 39, No. 4 ( 2012-04), p. 2042-2048
Abstract:
To evaluate Hotelling's T 2 statistic and the input variable squared prediction error ( Q ( X ) ) for detecting large respiratory surrogate‐based tumor displacement prediction errors without directly measuring the tumor's position. Methods: Tumor and external marker positions from a database of 188 Cyberknife Synchrony™ lung, liver, and pancreas treatment fractions were analyzed. The first ten measurements of tumor position in each fraction were used to create fraction‐specific models of tumor displacement using external surrogates as input; the models were used to predict tumor position from subsequent external marker measurements. A partial least squares (PLS) model with four scores was developed for each fraction to determine T 2 and Q ( X ) confidence limits based on the first ten measurements in a fraction. The T 2 and Q ( X ) statistics were then calculated for every set of external marker measurements. Correlations between model error and both T 2 and Q ( X ) were determined. Receiver operating characteristic analysis was applied to evaluate sensitivities and specificities of T 2 , Q ( X ) , and T 2 ∪ Q ( X ) for predicting real‐time tumor localization errors 〉 3 mm over a range of T 2 and Q ( X ) confidence limits. Results: Sensitivity and specificity of detecting errors 〉 3 mm varied with confidence limit selection. At 95% sensitivity, T 2 ∪ Q ( X ) specificity was 15%, 2% higher than either T 2 or Q ( X ) alone. The mean time to alarm for T 2 ∪ Q ( X ) at 95% sensitivity was 5.3 min but varied with a standard deviation of 8.2 min. Results did not differ significantly by tumor site. Conclusions: The results of this study establish the feasibility of respiratory surrogate‐based online monitoring of real‐time respiration‐induced tumor motion model accuracy for lung, liver, and pancreas tumors. The T 2 and Q ( X ) statistics were able to indicate whether inferential model errors exceeded 3 mm with high sensitivity. Modest improvements in specificity were achieved by combining T 2 and Q ( X ) results.
Type of Medium:
Online Resource
ISSN:
0094-2405
,
2473-4209
Language:
English
Publisher:
Wiley
Publication Date:
2012
detail.hit.zdb_id:
1466421-5
