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Sensitivity of volumetric modulated arc therapy patient specific QA results to multileaf collimator errors and correlation to dose volume histogram based metrics
Author(s) -
Coleman Linda,
Skourou Christina
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 - 10.1118/1.4824433
Subject(s) - multileaf collimator , dose volume histogram , nuclear medicine , metric (unit) , mathematics , imaging phantom , quality assurance , histogram , dosimetry , sensitivity (control systems) , correlation , medicine , statistics , radiation treatment planning , radiation therapy , computer science , artificial intelligence , radiology , operations management , external quality assessment , pathology , electronic engineering , engineering , economics , image (mathematics) , geometry
Purpose: This study investigates the impact of systematic multileaf collimator (MLC) positional errors on gamma analysis results used for quality assurance (QA) of Rapidarc treatments. In addition, this study evaluates the relationship of these gamma analysis results and clinical dose volume histogram metrics (DVH) for Rapidarc treatment plans.Methods: Five prostate plans were modified by the introduction of systematic MLC errors. The MLC shifts to each individual active leaf introduced were 0.25, 0.5, 0.75, and 1 mm. All QA verification plans were delivered and estimated 3D patient dose or high density phantom dose were obtained based on the ArcCHECK measurement files. QA gamma analysis of 3%/3 mm and 2%/2 mm were implemented and relationships to dose differences in DVH metrics encountered due to MLC errors were determined. Tolerances of 3% and 5% for DVH metric were implemented to determine the sensitivity of gamma analysis to MLC errors. A calculation of sensitivity was determined from the number of incidences of false negative and false positive cases in gamma analysis results.Results: The sensitivity of global gamma analysis for criteria of 3%/3 mm was 0.78 and for 2%/2 mm was 0.82. A number of instances occurred for an acceptable VMAT QA gamma index which did not indicate a DVH metric dose error greater than 5%. The correlation between global gamma analysis using criteria 3%/3 mm and DVH metric dose error were all <0.8 indicating less than a strong correlation.Conclusions: There is a greater sensitivity for detection of dosimetric errors occurring in a Rapidarc plan using gamma criteria of 2%/2 mm than 3%/3 mm. However, there is lack of consistently strong correlation between global gamma indexes and clinical DVH metrics for PTV and bladder and rectum for Rapidarc plans. It is recommended that the sole use of gamma index for Rapidarc QA plan evaluation could be insufficient and a methodology for evaluation of delivered dose to patient is required.