Quality assurance of volumetric modulated arc therapy: Evaluation and comparison of different dosimetric systems

Masi, Laura; Casamassima, F.; Doro, R.; Francescon, P.

doi:10.1118/1.3533900

Cited by 72 publications

(58 citation statements)

References 41 publications

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“…In either case, it is important to know how sensitive a particular dosimetric technique, paired to a particular linac, is to MLC leaf position errors as well as other rotational or translational errors that could compromise quality. Masi et al 52 reported recently that DELTA4 and MAPCHECK dosimetric systems for VMAT QA varied in sensitivity for some plans, where a 3…”

Section: Discussionmentioning

confidence: 99%

Is RapidArc more susceptible to delivery uncertainties than dynamic IMRT?

Betzel

Niu

et al. 2012

Medical Physics

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Purpose: Rotational IMRT has been adopted by many clinics for its promise to deliver treatments in a shorter amount of time than other conventional IMRT techniques. In this paper, the authors investigate whether RapidArc is more susceptible to delivery uncertainties than dynamic IMRT using fixed fields. Methods: Dosimetric effects of delivery uncertainties in dose rate, gantry angle, and MLC leaf positions were evaluated by incorporating these uncertainties into RapidArc and sliding window IMRT (SW IMRT) treatment plans for five head-and-neck and five prostate cases. Dose distributions and dose-volume histograms of original and modified plans were recalculated and compared using Gamma analysis and dose indices of planned treatment volumes (PTV) and organs at risk (OAR). Results of Gamma analyses using passing criteria ranging from 1%-1 mm up to 5%-3 mm were reported. Results: Systematic shifts in MLC leaf bank positions of SW-IMRT cases resulted in 2-4 times higher average percent differences than RapidArc cases. Uniformly distributed random variations of 2 mm for active MLC leaves had a negligible effect on all dose distributions. Sliding window cases were much more sensitive to systematic shifts in gantry angle. Dose rate variations during RapidArc must be much larger than typical machine tolerances to affect dose distributions significantly; dynamic IMRT is inherently not susceptible to such variations. Conclusions: RapidArc deliveries were found to be more tolerant to variations in gantry position and MLC leaf position than SW IMRT. This may be attributed to the fact that the average segmental field size or MLC leaf opening is much larger for RapidArc. Clinically acceptable treatments may be delivered successfully using RapidArc despite large fluctuations in dose rate and gantry position.

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Section: Discussionmentioning

confidence: 99%

Is RapidArc more susceptible to delivery uncertainties than dynamic IMRT?

Betzel

Niu

et al. 2012

Medical Physics

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“…Other assemblies furnish dosimetric data corresponding to the gantry position using phantoms characterized by opportune geometries or rotation capability, as SunNuclear ArcCHECK ® , Scandidos Delta4 ® phantom, the IBA Compass, and PTW Octavius ® ‐4D. Many studies report a comparison of these devices, assessing their different responses as well as their ability in detecting intentional errors,4, 5, 6 or they were used in the validation process of novel QA strategies 7, 8. The present study is focused on PTW Octavius ® ‐4D.…”

Section: Introductionmentioning

confidence: 99%

Practical application of Octavius^®‐4D: Characteristics and criticalities for IMRT and VMAT verification

Urso

Lorusso

Marzoli

et al. 2018

J Applied Clin Med Phys

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Octavius®‐4D is a very effective device in radiotherapy treatment quality assurance (QA), due to its simple set‐up and analysis package. However, even if it is widely used, its main characteristics and criticalities were only partially investigated. Taking start from its commissioning, the aim of this work was to study the main dependencies of the device response. The outcome dependence was studied comparing results by different delivery techniques [Intensity Modulated Radiation Therapy, IMRT (n = 29) and RapidArc, RA (n = 15)], anatomical regions [15 head/neck, 19 pelvis and 10 pancreas] and linear accelerators [DHX (n = 14) and Trilogy (n = 30)]. Moreover, the agreement dependency on the section of the phantom was assessed. Plan evaluations obtained by 2D, 3D, and volumetric γ‐index (both local and global) were also compared. Generally, high dose gradient resulted critically managed by the assembly, with a smoother effect in RA technique. Worse agreements emerged in the 2D γ‐index vs those of 3D and volumetric (P < 0.001), that were instead statistically comparable in global metric (P > 0.300). Volumetric plan evaluation was coherent with the average of passing rates on the 3 phantom axes (r ≥ 0.9), but transversal section provided best agreements vs sagittal and coronal ones (P < 0.050). The three studied districts furnished comparable results (P > 0.050) while the two LINACs provided different agreements (P < 0.005). The study pointed out that the phantom transversal section better fits the planned dose distribution, so this should be accounted when a two‐dimensional evaluation is needed. Moreover, the major reliability of the 3D metric with respect to the 2D one, as it better agrees with the dosimetric evaluation on the whole volume, suggests that it should be preferred in a two‐dimensional evaluation. Better agreements, obtained with RA vs IMRT technique, confirm that Octavius®‐4D is specifically conceived for rotational delivery. Lastly, the assembly resulted sensitive to different technology.

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“…Korreman et al (10) demonstrated the delivered dose distribution measured with a diode array to be in agreement with the TPS for over 96% of points in the gamma maps calculated at 3% and 3 mm. Masi et al (11) developed a protocol for dosimetric verification of VMAT, which compares TPS dose distributions to the one measured with film (radiographic and GAFCHROMIC), a diode or an ionization chamber array. Although the authors provided extensive analysis using gamma maps and investigated delivery faults, including linear shift of the leafs and the gantry offset, they did not address the concept of the DLG, which is a part of QA of VMAT.…”

Section: Introductionmentioning

confidence: 99%

On using the dosimetric leaf gap to model the rounded leaf ends in VMAT/RapidArc plans

Szpala

Cao

Kohli

2014

J Applied Clin Med Phys

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Partial transmission through rounded leaf ends of Varian multileaf collimators (MLC) is accounted for with a parameter called the dosimetric leaf gap (DLG). Verification of the value of the DLG is needed when the dose delivery is accompanied by gantry rotation in VMAT plans. We compared the doses measured with GAFCHROMIC film and an ionization chamber to treatment planning system (TPS) calculations to identify the optimum values of the DLG in clinical plans of the whole brain with metastases transferred to a phantom. We noticed the absence of a single value of the DLG that properly models all VMAT plans in our cohort (the optimum DLG varied between 0.93±0.15 mm and 2.2±0.2 mm). The former value is considerably different from the optimum DLG in sliding window plans (about 2.0 mm) that approximate IMRT plans. We further found that a single‐value DLG model cannot accurately reproduce the measured dose profile even of a uniform static slit at a fixed gantry, which is the simplest MLC‐delimited field. The calculation overestimates the measurement in the proximal penumbra, while it underestimates in the distal penumbra. This prompted us to expand the DLG parameter from a plan‐specific number to a mathematical concept of the DLG being a function of the distance in the beam's eye view (BEV) between the dose point and the leaf ends. Such function compensates for the difference between the penumbras in a beam delimited with a rounded leaf MLC and delimited with solid jaws. Utilization of this concept allowed us generating a pair of step‐and‐shoot MLC plans for which we could qualitatively predict the value of the DLG providing best match to ionization chamber measurements. The plan for which the leafs stayed predominantly at positions requiring low values of the DLG (as seen in the profiles of 1D slits) yielded the combined DLG of 1.1±0.2 mm, while the plan with leafs staying at positions requiring larger values of the DLG yielded the DLG 2.4±0.2 mm. Considering the DLG to be a function of the distance (in BEV) between the dose point and the leaf ends allowed us to provide an explanation as to why conventional single‐number DLG is plan‐specific in VMAT plans.PACS numbers: 87.56.jf, 87.56.nk

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Quality assurance of volumetric modulated arc therapy: Evaluation and comparison of different dosimetric systems

Cited by 72 publications

References 41 publications

Is RapidArc more susceptible to delivery uncertainties than dynamic IMRT?

Is RapidArc more susceptible to delivery uncertainties than dynamic IMRT?

Practical application of Octavius^®‐4D: Characteristics and criticalities for IMRT and VMAT verification

On using the dosimetric leaf gap to model the rounded leaf ends in VMAT/RapidArc plans

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Quality assurance of volumetric modulated arc therapy: Evaluation and comparison of different dosimetric systems

Cited by 72 publications

References 41 publications

Is RapidArc more susceptible to delivery uncertainties than dynamic IMRT?

Is RapidArc more susceptible to delivery uncertainties than dynamic IMRT?

Practical application of Octavius®‐4D: Characteristics and criticalities for IMRT and VMAT verification

On using the dosimetric leaf gap to model the rounded leaf ends in VMAT/RapidArc plans

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Practical application of Octavius^®‐4D: Characteristics and criticalities for IMRT and VMAT verification