Dosimetric Quality Assurance for Intensity–Modulated Radiotherapy

Wiezorek, Tilo; Banz, Nico; Schwedas, Michael; Scheithauer, Marcel; Salz, Henning; Georg, Dietmar; Wendt, Thomas

doi:10.1007/s00066-005-1381-z

Cited by 70 publications

(73 citation statements)

References 15 publications

(16 reference statements)

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“…Several authors have studied the sensitivity and reproducibility parameters of this array and the results obtained are comparable with similar, commonly used detectors. ( 7 , 9 ) The VeriSoft software (PTW‐Freiburg, Germany) was used to record radiation dose readings. The array was optically aligned with the MLC so that each leaf corresponded to one row of detectors.…”

Section: Methodsmentioning

confidence: 99%

“…2D arrays of detectors could be considered a solution for replacing radiographic films; ( 7 ) however, their low spatial resolution limits their applicability in resolving position errors in the order of few millimeters. The following work shows that this limitation can be solved by taking into account the fact that partial coverage of a volumetric detector by a radiation beam gives a response proportional to the irradiated volume, as described by Yang et al ( 8 ) Spezi et al ( 9 ) studied the response of a 2D ion chamber array when radiation fields gradually increase the coverage of the detector area, and found a close correspondence between detector coverage and its response.…”

Section: Introductionmentioning

confidence: 99%

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A method to enhance spatial resolution of a 2D ion chamber array for quality control of MLC

Moreno

Venencia

Garrigo

et al. 2011

J Applied Clin Med Phys

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This work introduces a new method for verifying MLC leaf positions with enough spatial resolution to replace film‐based methods in performing QA tests. It is implemented on a 2D ion chamber array, and it is based on the principle of varying signal response of a volumetric detector to partial irradiation. A PTW 2D‐ARRAY seven29 (PTW‐729 2D) array was used to assess a Siemens OPTIFOCUS MLC. Partial volume response curves for chambers in the array were obtained by irradiating them with the leaves of the MLC, progressively covering varying portions of the chambers correlated with the leaf positions. The readings from the array's chambers are processed with an in‐house program; it generates a reference response that translates readings into leaf positions. This principle allows discriminating errors in pairs of opposing leaves that could combine to cancel their detection with other tools.Patterns of leaf positions, similar to the Bayouth test but with different, purposefully introduced errors, were generated and used to test the effectiveness of the method. The same patterns were exposed on radiographic film and analyzed with the RIT software for validation. For four test patterns with a total of 100 errors of ±1 mm, ±2 mm and ±3 mm, all were correctly determined with the proposed method. The analysis of the same pattern with film using the Bayouth routine in the RIT software resulted in either somewhat low true positives combined with a large fraction of false positives, or a low true positive rate with a low false positive ratio, the results being significantly affected by the threshold selected for the analysis.This method provides an effective, easy to use tool for quantitative MLC QA assessment, with excellent spatial resolution. It can be easily applied to other 2D arrays, as long as they exhibit a partial volume detector response.PACS number: 87.55.Qr

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A method to enhance spatial resolution of a 2D ion chamber array for quality control of MLC

Moreno

Venencia

Garrigo

et al. 2011

J Applied Clin Med Phys

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“…The MatriXX array has a linear response with dose and it is independent of energy [12]. Additionally, the system provides results comparable with those of the film and various point dose detectors [15,16]. However, it has the major limitation of angular dependence; specifically, a 7%-11% dose discrepancy was reported by Wolfsberger et al for beam incidence in the perpendicular and oblique directions [11].…”

Section: Introductionmentioning

confidence: 92%

Study of impacts of different evaluation criteria on gamma pass rates in VMAT QA using MatriXX and EPID

Noufal

Abdullah

Puzhakkal

et al. 2017

Polish Journal of Medical Physics and Engineering

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Aim: This study evaluates the impacts of using different evaluation criteria on gamma pass rates in two commercially available QA methods employed for the verification of VMAT plans using different hypothetical planning target volumes (PTVs) and anatomical regions. Introduction: Volumetric modulated arc therapy (VMAT) is a widely accepted technique to deliver highly conformal treatment in a very efficient manner. As their level of complexity is high in comparison to intensity-modulated radiotherapy (IMRT), the implementation of stringent quality assurance (QA) before treatment delivery is of paramount importance. Material and Methods: Two sets of VMAT plans were generated using Eclipse planning systems, one with five different complex hypothetical three-dimensional PTVs and one including three anatomical regions. The verification of these plans was performed using a MatriXX ionization chamber array embedded inside a MultiCube phantom and a Varian EPID dosimetric system attached to a Clinac iX. The plans were evaluated based on the 3%/3 mm, 2%/2 mm, and 1%/1 mm global gamma criteria and with three low-dose threshold values (0%, 10%, and 20%). Results: The gamma pass rates were above 95% in all VMAT plans, when the 3%/3mm gamma criterion was used and no threshold was applied. In both systems, the pass rates decreased as the criteria become stricter. Higher pass rates were observed when no threshold was applied and they tended to decrease for 10% and 20% thresholds. Conclusion: The results confirm the suitability of the equipments used and the validity of the plans. The study also confirmed that the threshold settings greatly affect the gamma pass rates, especially for lower gamma criteria.

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“…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

J Applied Clin Med Phys

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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.

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Dosimetric Quality Assurance for Intensity–Modulated Radiotherapy

Abstract: Commercial 2-D detectors have the potential to replace films as an "area detector" for field-related verification of IMRT. The on-line information provided by the respective systems can even improve the efficiency of the QA procedures.

Cited by 70 publications

References 15 publications

A method to enhance spatial resolution of a 2D ion chamber array for quality control of MLC

A method to enhance spatial resolution of a 2D ion chamber array for quality control of MLC

Study of impacts of different evaluation criteria on gamma pass rates in VMAT QA using MatriXX and EPID

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

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