Evaluation of a 2D diode array for IMRT quality assurance

An effective patient quality assurance (QA) program for intensity‐modulated radiation therapy (IMRT) requires accurate and realistic plan acceptance criteria—that is, action limits. Based on dose measurements performed with a commercially available two‐dimensional (2D) diode array, we analyzed 747 fluence maps resulting from a routine patient QA program for IMRT plans. The fluence maps were calculated by three different commercially available (ADAC, CMS, Eclipse) treatment planning systems (TPSs) and were delivered using 6‐MV X‐ray beams produced by linear accelerators. To establish reasonably achievable and clinically acceptable limits for the dose deviations, the agreement between the measured and calculated fluence maps was evaluated in terms of percent dose error (PDE) for a few points and percent of passing points (PPP) for the isodose distribution. The analysis was conducted for each TPS used in the study (365 ADAC, 162 CMS, 220 Eclipse), for multiple treatment sites (prostate, pelvis, head and neck, spine, rectum, anus, lung, brain), at the normalization point for 3% percentage difference (%Diff) and 3‐mm distance to agreement (DTA) criteria. We investigated the treatment‐site dependency of PPP and PDE. The results show that, at 3% and 3‐mm criteria, a 95% PPP and 3% PDE can be achieved for prostate treatments and a 90% PPP and 5% PDE are attainable for any treatment site.PACS Numbers: 87.53Dq, 87.53Tf, 87.53Xd, 87.56Fc

Section: Introductionmentioning

confidence: 99%

A study to establish reasonable action limits for patient‐specific quality assurance in intensity‐modulated radiation therapy

Both

Alecu

Stan³

et al. 2007

“…The SNC user's manual lists several uncertainties approximately quantified and included in the Measurement Uncertainty function. These include an array calibration correction (approximated from a study dealing with the original MapCHECK device), (21) a correction for assumed accelerator output and room temperature differences between the time of array calibration and actual measurement, and a correction for an assumed error in setup source‐to‐surface distance (SSD). The user should decide whether or not these enumerated uncertainties (and their approximate values used to supplement the %Diff criteria) are applicable to one's own measurement conditions.…”

Section: Resultsmentioning

confidence: 99%

“…Planar diode arrays are a standard tool for myriad external beam quality assurance tests, most popularly for patient‐specific dosimetric verification of intensity‐modulated radiation therapy fields, 1 , 2 for both static 3 , 4 and rotational 5 , 6 delivery techniques. One of the diode arrays most commonly used for planar dose measurement is the MapCHECK 7 , 8 device (and its upgrade, the MapCHECK 2) 9 , 10 , 11 by Sun Nuclear Corporation of Melbourne, FL, accompanied by its analytical software component (i.e., “MapCHECK” up to version 5.2; “SNC Patient” thereafter).…”

Section: Introductionmentioning

confidence: 99%

The MapCHECK Measurement Uncertainty function and its effect on planar dose pass rates

Bailey

Spaans

Kumaraswamy

et al. 2016

Our study aimed to quantify the effect of the Measurement Uncertainty function on planar dosimetry pass rates, as measured and analyzed with the Sun Nuclear Corporation MapCHECK 2 array and its associated software. This optional function is toggled in the program preferences of the software (though turned on by default upon installation), and automatically increases the dose difference tolerance defined by the user for each planar dose comparison. Dose planes from 109 static‐gantry IMRT fields and 40 VMAT arcs, of varying modulation complexity, were measured at 5 cm water‐equivalent depth in the MapCHECK 2 diode array, and respective calculated dose planes were exported from a commercial treatment planning system. Planar dose comparison pass rates were calculated within the Sun Nuclear Corporation analytic software using a number of calculation parameters, including Measurement Uncertainty on and off. By varying the percent difference (%Diff) criterion for similar analyses performed with Measurement Uncertainty turned off, an effective %Diff criterion was defined for each field/arc corresponding to the pass rate achieved with Measurement Uncertainty turned on. On average, the Measurement Uncertainty function increases the user‐defined %Diff criterion by 0.8%‐1.1% for 3%/3 mm analysis, depending on plan type and calculation technique (corresponding to an average change in pass rate of 1.0%‐3.5%, and a maximum change of 8.7%). At the 2%/2 mm level, the Measurement Uncertainty function increases the user‐defined %Diff criterion by 0.7%‐1.2% on average, again depending on plan type and calculation technique (corresponding to an average change in pass rate of 3.5%‐8.1%, and a maximum change of 14.2%). The largest increases in pass rate due to the Measurement Uncertainty function are generally seen with poorly matched planar dose comparisons, while the function has a notably smaller effect as pass rates approach 100%. The Measurement Uncertainty function, then, may substantially increase the pass rates for planar dose comparisons. Meanwhile, the types of uncertainties incorporated into the function (and their associated quantitative estimates, as described in the software user's manual) may not be an accurate estimation of actual measurement uncertainty, depending on the user's measurement conditions. Pass rates listed in published reports, comparisons between institutions or simply separate workstations, or comparisons with the calculation methods of other vendors, should clearly indicate whether or not the Measurement Uncertainty function is used, since it has the potential to substantially inflate pass rates for typical IMRT and VMAT dose planes.PACS number(s): 87.55.Qr, 87.56.Fc

“…The complexity of the systems involved requires new and appropriate methods and potentially new tools in order to do this. Several devices dedicated to daily QA have been developed that can be used for IMRT and VMAT verification 6 , 7 , 8 , 9 , 10 , 11 , 12 …”

Section: Introductionmentioning

confidence: 99%

“…2D semiconductor based on diodes approaches, such as MapCHECK (Sun Nuclear Corp., Melbourne, FL) 5 , 11 , 19 , 20 , 21 and the quality control (QA) device, (22) have also been used for dose verification. Electronic portal imaging devices (EPIDs) have also been tested for in vivo dosimetry purposes (12) .…”

Section: Introductionmentioning

confidence: 99%

Beam perturbation characteristics of a 2D transmission silicon diode array, Magic Plate

Alrowaili

Lerch

Petasecca

et al. 2016

The main objective of this study is to demonstrate the performance characteristics of the Magic Plate (MP) system when operated upstream of the patient in transmission mode (MPTM). The MPTM is an essential component of a real‐time QA system designed for operation during radiotherapy treatment. Of particular interest is a quantitative study into the influence of the MP on the radiation beam quality at several field sizes and linear accelerator potential differences. The impact is measured through beam perturbation effects such as changes in the skin dose and/or percentage depth dose (PDD) (both in and out of field). The MP was placed in the block tray of a Varian linac head operated at 6, 10 and 18 MV beam energy. To optimize the MPTM operational setup, two conditions were investigated and each setup was compared to the case where no MP is positioned in place (i.e., open field): (i) MPTM alone and (ii) MPTM with a thin passive contamination electron filter. The in‐field and out‐of‐field surface doses of a solid water phantom were investigated for both setups using a Markus plane parallel (Model N23343) and Attix parallel‐plate, MRI model 449 ionization chambers. In addition, the effect on the 2D dose distribution measured by the Delta4 QA system was also investigated. The transmission factor for both of these MPTM setups in the central axis was also investigated using a Farmer ionization chamber (Model 2571A) and an Attix ionization chamber. Measurements were performed for different irradiation field sizes of 5×5 cm2 and 10×10 cm2. The change in the surface dose relative to dmax was measured to be less than 0.5% for the 6 MV, 10 MV, and 18 MV energy beams. Transmission factors measured for both set ups (i & ii above) with 6 MV, 10 MV, and 18 MV at a depth of dmax and a depth of 10 cm were all within 1.6% of open field. The impact of both the bare MPTM and the MPTM with 1 mm buildup on 3D dose distribution in comparison to the open field investigated using the Delta4 system and both the MPTM versions passed standard clinical gamma analysis criteria. Two MPTM operational setups were studied and presented in this article. The results indicate that both versions may be suitable for the new real‐time megavoltage photon treatment delivery QA system under development. However, the bare MPTM appears to be slightly better suited of the two MP versions, as it minimally perturbs the radiation field and does not lead to any significant increase in skin dose to the patient.PACS number(s): 87.50.up, 87.53.Bn, 87.55.N, 87.55.Qr, 87.56.Fc.