Premium
SU‐E‐T‐185: Passing Rates of 83 Patient‐Specific IMRT QA Measurements with ArcCHECK Using Various Gamma Criteria
Author(s) -
Sintay B,
Ramer T,
Wiant D
Publication year - 2011
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 - 10.1118/1.3612135
Subject(s) - tomotherapy , quality assurance , nuclear medicine , voxel , ionization chamber , dosimetry , medicine , radiation therapy , mathematics , medical physics , physics , radiology , ion , external quality assessment , pathology , quantum mechanics , ionization
Purpose: Three‐dimensional diode arrays are an important tool in patient‐specific intensity modulated radiotherapy quality assurance (IMRT QA) for arc therapy. We investigated the results of 83 patient‐specific IMRT QA measurements made on TomoTherapy using the Sun Nuclear ArcCHECK. Methods: Our ArcCHECK setup consists of a water‐equivalent plug and ion chamber at the center of the device. Planned dose is recalculated for ArcCHECK using the TomoTherapy planning workstation on the “Normal” setting creating dose voxels sized 4.8mm in each dimension. Patient‐specific IMRT QA measurements are made for all patients on TomoTherapy using megavoltage computed tomography to register the device. Analysis is performed in Sun Nuclearˈs MapCHECK software using various dose difference and distance gamma criteria using absolute dose (AD). The average passing rates, uncertainty, and upper/lower quartiles (UQ and LQ) of the data were computed. Four measurements deemed unacceptable were left in the data to determine the number of false negatives (FN) and false positives (FP) given when using various passing thresholds. Results: The average passing rates using gamma criteria 5%/5mm, 5%/3mm, 3%/5mm, 3%/3mm, 2%/5mm, 2%/3mm, 1%/5mm and 1%/3mm were 99.7 +/−0.5%, 98.4 +/−1.9%, 98.6 +/−1.5%, 94.9 +/−3.5%, 97.0 +/2.5%, 90.4 +/−5.1%, 94.1 +/−4.6% and 83.6 +/−7.1% respectively. The distribution of points passing using 2%/5mm (UQ 98.8 LQ 95.8) was significantly better than the typical criteria of 3%/3mm (UQ 97.8 LQ 92.7). 2%/5mm were the only criteria that gave no FN or FP using a percentage of points passing threshold of 93%. At this threshold 3%/3mm produced 21 FN and 1 FP. Conclusions: The performance of various criteria at or below the 3% dose difference threshold demonstrates improved results using 5mm as the distance parameter. This is likely due to the “Normal” dose voxel size in TomoTherapy and has led us to investigate using the “Fine” dose grid of 2.4mm.