Evaluation of the ArcCHECK QA system for IMRT and VMAT verification

Many devices designed for the purpose of performing patient‐specific IMRT/VMAT QA are commercially available. In this work we report our experience and initial clinical results with the ArcCHECK. The ArcCHECK consists of a cylindrical array of diode detectors measuring entry and exit doses. The measured result is a cumulative dose displayed as a 2D matrix. The detector array requires both an absolute dose calibration, and a calibration of the detector response, relative to each other. In addition to the calibrations suggested by the manufacturer, various tests were performed in order to assess its stability and performance prior to clinical introduction. Tests of uniformity, linearity, and repetition rate dependence of the detector response were conducted and described in this work. Following initial testing, the ArcCHECK device was introduced in the clinic for routine patient‐specific IMRT QA. The clinical results from one year of use were collected and analyzed. The gamma pass rates at the 3%/3 mm criterion were reported for 3,116 cases that included both IMRT and VMAT treatment plans delivered on 18 linear accelerators. The gamma pass rates were categorized based on the treatment site, treatment technique, type of MLCs, operator, ArcCHECK device, and LINAC model. We recorded the percent of failures at the clinically acceptable threshold of 90%. In addition, we calculated the threshold that encompasses two standard deviations (2 SD) (95%) of QAs (T95) for each category investigated. The commissioning measurements demonstrated that the device performed as expected. The uniformity of the detector response to a constant field arc delivery showed a 1% standard deviation from the mean. The variation in dose with changing repetition rate was within 1 cGy of the mean, while the measured dose showed a linear relation with delivered MUs. Our initial patient QA results showed that, at the clinically selected passing criterion, 4.5% of cases failed. On average T95 was 91%, ranging from 73% for gynecological sites to 96.5% for central nervous system sites. There are statistically significant differences in passing rates between IMRT and VMAT, high‐definition (HD) and non‐HD MLCs, and different LINAC models (p‐values <<0.001). An additional investigation into the failing QAs and a comparison with ion‐chamber measurements reveals that the differences observed in the passing rates between the different studied factors can be largely explained by the field size dependence of the device. Based on our initial experience with the ArcCHECK, our passing rates are, on average, consistent with values reported in the AAPM TG‐119. However, the significant variations between QAs that were observed based on the size of the treatment fields may need to be corrected to improve the specificity and sensitivity of the device.PACS number(s): 87.55.Qr, 87.56.Fc

“…This field size dependence was confirmed by Li et al, (15) who reported a 1.7% increase in sensitivity of the detectors for a

20 \times 20 {cm}^{2}

Section: Discussionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Initial clinical experience with ArcCHECK for IMRT/VMAT QA

Aristophanous

Suh

et al. 2016

“…In all cases the device performed within specifications and/or substantially equivalent to the previous version 4 , 5 , 14 …”

Section: Methodsmentioning

confidence: 94%

Validation of an improved helical diode array and dose reconstruction software using TG‐244 datasets and stringent dose comparison criteria

Ahmed

Nelms²,

Kozelka

et al. 2016

The original helical ArcCHECK (AC) diode array and associated software for 3D measurement‐guided dose reconstruction were characterized and validated; however, recent design changes to the AC required that the subject be revisited. The most important AC change starting in 2014 was a significant reduction in the overresponse of diodes to scattered radiation outside of the direct beam, accomplished by reducing the amount of high‐Z materials adjacent to the diodes. This change improved the diode measurement accuracy, but in the process invalidated the dose reconstruction models that were assembled based on measured data acquired with the older version of the AC. A correction mechanism was introduced in the reconstruction software (3DVH) to accommodate this and potential future design changes without requiring updating model parameters. For each permutation of AC serial number and beam model, the user can define in 3DVH a single correction factor which will be used to compensate for the difference in the out‐of‐field response between the new and original AC designs. The exact value can be determined by minimizing the dose‐difference with an ionization chamber or another independent dosimeter. A single value of 1.17, corresponding to the maximum measured out‐of‐field response difference between the new and old AC, provided satisfactory results for all studied energies (6X, 15X, and flattening filter‐free 10XFFF). A library of standard cases recommended by the AAPM TG‐244 Report was used for reconstructed dose verification. The overall difference between reconstructed dose and an ion chamber in a water‐equivalent phantom in the targets was 0.0% ± 1.4% (1 SD). The reconstructed dose on a homogeneous phantom was also compared to a biplanar diode dosimeter (Delta4) using gamma analysis with 2% (local dose‐error normalization)/2 mm/10% cutoff criteria. The mean agreement rate was 96.7% ± 3.7%. For the plans common with the previous comparison, the mean agreement rate was 98.3% ± 0.8%, essentially unchanged. We conclude that the proposed software modification adequately addresses the change in the dosimeter response.PACS number(s): 87.55Qr

“…Currently, the electronic dosimetry system is still more popular in clinic use for patient‐specific QA because of its easy handling and the reproducibility. The electronic dosimetry systems with various geometry configurations and detector types introduced for routine patient‐specific QA for linac‐based treatments include planar ion chamber/diode arrays 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 (e.g., MatriXX, IBA Dosimetry; Octavius 729, PTW; MapCHECK, SunNclear Corp.), cylindrical diode arrays 16 , 17 , 18 , 19 , 20 , 21 , 22 (ArcCHECK, Sun Nuclear Corp), and two diode arrays embedded in a cross‐plane fashion in a cylindrical phantom (23) (Delta 4 , ScandiDos AB, Uppsala, Sweden). In contrast to the measurements for the linac delivery, which are mostly in a coplanar manner with larger field sizes, the measurements for the CyberKnife delivery can be more challenging since the delivery involves numerous narrow unflattened photon beams at a wide range of spatial angles.…”

Section: Introductionmentioning

confidence: 99%

Robotic radiosurgery system patient‐specific QA for extracranial treatments using the planar ion chamber array and the cylindrical diode array

Lin

Veltchev

Koren

et al. 2015

Robotic radiosurgery system has been increasingly employed for extracranial treatments. This work is aimed to study the feasibility of a cylindrical diode array and a planar ion chamber array for patient‐specific QA with this robotic radiosurgery system and compare their performance. Fiducial markers were implanted in both systems to enable image‐based setup. An in‐house program was developed to postprocess the movie file of the measurements and apply the beam‐by‐beam angular corrections for both systems. The impact of noncoplanar delivery was then assessed by evaluating the angles created by the incident beams with respect to the two detector arrangements and cross‐comparing the planned dose distribution to the measured ones with/without the angular corrections. The sensitivity of detecting the translational (1–3 mm) and the rotational (1°–3°) delivery errors were also evaluated for both systems. Six extracranial patient plans (PTV 7–137 cm3) were measured with these two systems and compared with the calculated doses. The plan dose distributions were calculated with ray‐tracing and the Monte Carlo (MC) method, respectively. With 0.8 by 0.8 mm2 diodes, the output factors measured with the cylindrical diode array agree better with the commissioning data. The maximum angular correction for a given beam is 8.2% for the planar ion chamber array and 2.4% for the cylindrical diode array. The two systems demonstrate a comparable sensitivity of detecting the translational targeting errors, while the cylindrical diode array is more sensitive to the rotational targeting error. The MC method is necessary for dose calculations in the cylindrical diode array phantom because the ray‐tracing algorithm fails to handle the high‐Z diodes and the acrylic phantom. For all the patient plans, the cylindrical diode array/ planar ion chamber array demonstrate 100%/>;92%false(3%/3 mmfalse) passing rates. The feasibility of using both systems for robotic radiosurgery system patient‐specific QA has been demonstrated. For gamma evaluation, 2%/2 mm criteria for cylindrical diode array and 3%/3 mm criteria for planar ion chamber array are suggested. The customized angular correction is necessary as proven by the improved passing rate, especially with the planar ion chamber array system.PACS number: 29.40.‐n