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SU‐FF‐T‐314: Patient‐Specific Quality Assurance Techniques for RapidArc Radiotherapy
Author(s) -
O'Daniel J,
McMahon R,
Chang Z,
Yan H,
Sakhalkar H,
Das S,
Wu Q,
Yin F
Publication year - 2009
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 - 10.1118/1.3181794
Subject(s) - ionization chamber , quality assurance , nuclear medicine , dosimetry , materials science , radiation therapy , sagittal plane , dose rate , medical physics , medicine , ion , physics , radiology , external quality assessment , pathology , quantum mechanics , ionization
Purpose: To develop a patient‐specific quality assurance protocol for RapidArc™ radiotherapy. Method and Materials: Following the commissioning of RapidArc™ treatment delivery, we tested several methods of patient‐specific quality assurance (QA). Ion chamber and film measurements were used as the “gold standard”. One ion chamber measurement was taken in a region of low‐dose gradient. Four film measurements were taken in three planes: axial, sagittal, coronal, and a coronal180° (testing setup uncertainty). Measurements were also taken using the Matrixx® device (IBA Dosimetry, Bartlett, TN) in two orientations, sagittal and coronal. The Matrixx® consists of a 24×24cm 2 grid of ion chambers, providing a 2D absolute dose comparison. All plans were designed and calculated using Eclipse (Varian Medical Systems, Palo Alto, CA). Eleven patient plans were evaluated, consisting of 4 brain, 1 head&neck boost, and 6 prostate radiotherapy treatments. Results: Ion chamber measurements were typically ∼2% greater than those predicted by Eclipse. Using a gamma index with 3%, 3mm, 5% threshold criteria, 88% of films had gamma pass rates of >90%. Three of 7 axial films failed, but passed with thresholds of 30–40%. Similarly, Matrixx® measurements had gamma pass rates of >90% for 100% of measurements. The average reading of 4 Matrixx ion chambers was significantly correlated with the single ion chamber results (Pearson correlation coefficient = 0.839, p = 0.002), and the 2D Matrixx results agreed well with film measurements (gamma pass rate >90% for 10 of 11 comparisons). Conclusion: These QA measurements produced good agreement between planned and measured doses. Through utilizing ion chamber and film measurements, we have gained confidence in the Matrixx® for RapidArc QA. The chosen passing criteria were +/−3% for ion chamber readings, and gamma passing rates of >90% for film and Matrixx® with 3%, 3mm, and 5% threshold.