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ROC analysis in patient specific quality assurance
Author(s) -
Carlone Marco,
Cruje Charmainne,
Rangel Alejandra,
McCabe Ryan,
Nielsen Michelle,
MacPherson Miller
Publication year - 2013
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 - 10.1118/1.4795757
Subject(s) - quality assurance , multileaf collimator , sensitivity (control systems) , receiver operating characteristic , statistical power , mathematics , statistics , nuclear medicine , range (aeronautics) , computer science , medicine , medical physics , radiation treatment planning , radiation therapy , materials science , radiology , external quality assessment , pathology , electronic engineering , engineering , composite material
Purpose: This work investigates the use of receiver operating characteristic (ROC) methods in patient specific IMRT quality assurance (QA) in order to determine unbiased methods to set threshold criteria for γ ‐distance to agreement measurements.Methods: A group of 17 prostate plans was delivered as planned while a second group of 17 prostate plans was modified with the introduction of random multileaf collimator (MLC) position errors that are normally distributed with σ ∼±0.5, ±1.0, ±2.0, and ±3.0 mm (a total of 68 modified plans were created). All plans were evaluated using five different γ ‐criteria. ROC methodology was applied by quantifying the fraction of modified plans reported as “fail” and unmodified plans reported as “pass.”Results: γ ‐based criteria were able to attain nearly 100% sensitivity/specificity in the detection of large random errors ( σ > 3 mm). Sensitivity and specificity decrease rapidly for all γ ‐criteria as the size of error to be detected decreases below 2 mm. Predictive power is null with all criteria used in the detection of small MLC errors ( σ < 0.5 mm). Optimal threshold values were established by determining which criteria maximized sensitivity and specificity. For 3%/3 mm γ ‐criteria, optimal threshold values range from 92% to 99%, whereas for 2%/2 mm, the range was from 77% to 94%.Conclusions: The optimal threshold values that were determined represent a maximized test sensitivity and specificity and are not subject to any user bias. When applied to the datasets that we studied, our results suggest the use of patient specific QA as a safety tool that can effectively prevent large errors (e.g., σ > 3 mm) as opposed to a tool to improve the quality of IMRT delivery.