Influence of the Integral Quality Monitor transmission detector on high energy photon beams: A multi-centre study

Casar, Božidar; Pasler, Marlies; Wegener, Sonja; Hoffman, David C.; Talamonti, Cinzia; Qian, Jing; Méndez, Ignasi; Brojan, Denis; Perrin, B.; Kusters, Martijn; Canters, R.; Pallotta, S.; Peterlin, Primož

doi:10.1016/j.zemedi.2016.10.001

Cited by 20 publications

(35 citation statements)

References 23 publications

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“…The system's robustness, its stability in performance, basic error detection capabilities with regards to systematic errors in the form of a different number of MUs, wrong gantry angle or beam energy, as well as its high sensitivity for the detection of systematic errors in the leaf positions have been demonstrated . Furthermore, dosimetric changes in the delivered beam introduced by the system were subject of a previous study …”

Section: Introductionmentioning

confidence: 99%

Sensitivity of the IQM transmission detector to errors of VMAT plans

et al. 2018

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Purpose The integral quality monitor (IQM) transmission detector is a wedge‐shaped large area ionization chamber that reports a position‐weighted dose area product for each control point of an IMRT or VMAT plan. In this study, the accuracy of the signal prediction is verified for the Synergy Agility MLC. Tolerance criteria for VMAT plan verification with the IQM were obtained from the observed sensitivity for the detection of incorrectly delivered plans. Methods The predicted IQM signal was compared to the measured signal recorded for a set of 30 VMAT plans for each beam quality of 6 and 10 MV. The system's capability to detect incorrectly delivered plans was tested by measuring altered plans containing small, random deviations. In addition, the observed deviations were related to measurements performed with a second QA phantom. Results The cumulative IQM signal per arc deviated from the respective calculation on average by −0.48% (6 MV) and +0.21% (10 MV) with a standard deviation of 1.08% in both cases, suggesting a 2% warning and 3% action threshold as plan acceptance criteria. This choice was confirmed by the optimum threshold of 2.5% obtained via receiver operating characteristic (ROC) analysis. Reproducibility of individual control points in multiply measured plans was low (on average 7% for 1SD) and thus, segment‐by‐segment comparison was impractical. A suitable criterion to resolve the angular distribution of the plan was identified by binning three to five control points as a running average. While the correlation between IQM signal deviations and gamma passing rates obtained with the ArcCHECK phantom was low for clinical plans, it was apparent for erroneous plans. Binning led to even higher sensitivity to errors. Conclusions The IQM was able to detect induced errors at least as reliable as the standard phantom and showed the potential to be used in pretreatment plan verification to ensure the correct plan transfer and delivery. However, there is no direct correlation between the IQM signal deviation and DVH metrics, so the IQM should be primarily used to screen for errors. Finer diagnostics should then be carried out using a different phantom.

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Section: Introductionmentioning

confidence: 99%

Sensitivity of the IQM transmission detector to errors of VMAT plans

et al. 2018

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“…The integral quality monitor (IQM, i‐RT Systems GmbH, Koblenz, Germany) comprises one single ionization chamber with two non‐parallel electrode plates. A good description of the design is given by Casar et al The measure is an integral of the fluence consisting of one single AIMS signal and can be monitored in real‐time during the treatment.…”

Section: Methodsmentioning

confidence: 99%

“…All material inserted in the beam between beam source and the patient can alter beam characteristics, thus also transmission detectors. The influence of the IQM transmission detector on beam hardening, surface dose and transmission factor has already been investigated in a multicenter study . Some transmission detector effects that can influence patient dose delivery can be compensated for during the planning process, for example, by including them in the beam model.…”

Section: Introductionmentioning

confidence: 99%

“…Because of the disadvantages of objects inserted in the beam, our institution does not intend using the IQM detector for every treatment, but instead less frequently, for example, weekly. The transmission factor of the IQM detector has been determined at between 0.94 and 0.96 for single open fields, which is too low to be neglected even for a single fraction. Therefore a procedure is desired which takes the IQM transmission detector into account merely as a transmission factor for a limited number of treatments.…”

Section: Introductionmentioning

confidence: 99%

“…This will result in a slightly modified RT plan (RT mod ). For the IQM detector, it has been shown that there is only a small dependency of the TF with field sizes using regular static shapes . However, in VMAT treatment planning, the field sizes and shapes change continuously, with the field shapes being far removed from regular shapes.…”

Section: Introductionmentioning

confidence: 99%

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Technical Note: Alternating clinical usage of the integral quality monitor transmission detector

Kohler

Hanauer

2019

Medical Physics

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Purpose The purpose of the study was the implementation of a method to use the integral quality monitor (IQM) transmission detector for occasional, alternating usage during patient treatment with intensity modulated radiotherapy. Due to attenuation, the transmission detector must be taken into account during the planning process. The proposed workflow is based on determining a dynamic transmission factor (dTF) required to scale the total number of MU of the original radiotherapy (RT) plan. Thus a very similar radiation therapy plan is obtained that can be used with the IQM detector. Methods Ten clinically applied volumetric modulated arc therapy plans were delivered at two beam qualities. A dTF is calculated from each RT plan for which a collapsed RT plan was created for verification using a two‐dimensional array with and without the IQM detector. The total number of MU of the original RT plan was scaled by the inverse of the dTF to obtain the modified RT plan for clinical use with the IQM detector. Validation was performed with an electronic three‐dimensional phantom and via gamma analysis using strict criteria of 1%/1 mm. Results Except for one outlier, the gamma pass rate between the original RT plan without IQM and the modified RT plan with IQM was always above 99.5%. The variations of the dTF were smaller than 1% for all tested RT plans. Conclusions The results show that the proposed workflow can be used clinically. Thus the IQM transmission detector can also be used occasionally for online verification of RT plans.

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Two‐dimensional solid‐state array detectors: A technique for in vivo dose verification in a variable effective area

Utitsarn

Biasi

Stansook

et al. 2019

J Applied Clin Med Phys

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Purpose:We introduce a technique that employs a 2D detector in transmission mode (TM) to verify dose maps at a depth of d max in Solid Water. TM measurements, when taken at a different surface-to-detector distance (SDD), allow for the area at d max (in which the dose map is calculated) to be adjusted. Methods:We considered the detector prototype "MP512" (an array of 512 diodesensitive volumes, 2 mm spatial resolution). Measurements in transmission mode were taken at SDDs in the range from 0.3 to 24 cm. Dose mode (DM) measurements were made at d max in Solid Water. We considered radiation fields in the range from 2 × 2 cm 2 to 10 × 10 cm 2 , produced by 6 MV flattened photon beams;we derived a relationship between DM and TM measurements as a function of SDD and field size. The relationship was used to calculate, from TM measurements at 4 and 24 cm SDD, dose maps at d max in fields of 1 × 1 cm 2 and 4 × 4 cm 2 , and in IMRT fields. Calculations were cross-checked (gamma analysis) with the treatment planning system and with measurements (MP512, films, ionization chamber).Results: In the square fields, calculations agreed with measurements to within ±2.36%. In the IMRT fields, using acceptance criteria of 3%/3 mm, 2%/2 mm, 1%/ 1 mm, calculations had respective gamma passing rates greater than 96.89%, 90.50%, 62.20% (for a 4 cm SSD); and greater than 97.22%, 93.80%, 59.00% (for a 24 cm SSD). Lower rates (1%/1 mm criterion) can be explained by submillimeter misalignments, dose averaging in calculations, noise artifacts in film dosimetry.Conclusions: It is possible to perform TM measurements at the SSD which produces the best fit between the area at d max in which the dose map is calculated and the size of the monitored target. K E Y W O R D S2D solid-state array detector, MP512, transmission detector, in vivo QA

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Influence of the Integral Quality Monitor transmission detector on high energy photon beams: A multi-centre study

Cited by 20 publications

References 23 publications

Sensitivity of the IQM transmission detector to errors of VMAT plans

Sensitivity of the IQM transmission detector to errors of VMAT plans

Technical Note: Alternating clinical usage of the integral quality monitor transmission detector

Two‐dimensional solid‐state array detectors: A technique for in vivo dose verification in a variable effective area

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