Direct impact analysis of multi-leaf collimator leaf position errors on dose distributions in volumetric modulated arc therapy: a pass rate calculation between measured planar doses with and without the position errors

Tatsumi, Daisaku; Hosono, Masamichi; Nakada, Ryosei; Ishii, Kentaro; Tsutsumi, S.; Inoue, Makoto; Ichida, Takao; Miki, Yukio

doi:10.1088/0031-9155/56/20/n03

Cited by 39 publications

(36 citation statements)

References 13 publications

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“…35,36,42 Previous studies have reported on several types of MLC errors to observe their impact on patient dose distributions. In this study, a systematic shift in one leaf bank was sufficient to make a clear comparison between the two techniques, 39 but is not the most significant type of MLC error as shown in previous studies, e.g., both leaf banks open. 37,38,42 Large variability in sensitivity to MLC errors (D mean ) between cases was not seen as compared to a previous study.…”

Section: Discussionmentioning

confidence: 49%

“…They suggest that to create plans that are robust against MLC errors, the total MU should be minimized and MLC gaps should be as large as possible without sacrificing plan quality. Tatsumi et al 39 used three different treatment planning systems to create VMAT plans for five prostate cases and tested pass rates when systematic MLC leaf positions errors were introduced directly into the linac controller. They found that the impact of leaf position errors on dose distributions depended upon the final optimization result from each planning system due to a correlation between dose error and average leaf gap width.…”

Section: Introductionmentioning

confidence: 99%

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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: 49%

Section: Introductionmentioning

confidence: 99%

Is RapidArc more susceptible to delivery uncertainties than dynamic IMRT?

Betzel

Niu

et al. 2012

Medical Physics

View full text Add to dashboard Cite

show abstract

“…The detection sensitivity of MLC leaf positioning shifts has been studied with different devices 18, 19, 20, 21, 22. Yan et al 18.…”

Section: Discussionmentioning

confidence: 99%

“…conducted a sensitivity study with both ionization chamber and diode 2D array devices for prostate and head and neck VMAT delivery, and suggested Gamma index of 2%/2 mm with passing rate greater than 90% was necessary to detect leaf positioning shifts of 1 mm on both MLC banks. Unlike other studies mentioned above, which were based on planar doses comparison between measurement and calculation, Tatsumi et al 22. proposed a direct method for evaluating the impact of the leaf positioning shifts on dose distribution for prostate VMAT delivery by comparing the measured planar doses with and without shifts.…”

Section: Discussionmentioning

confidence: 99%

Sensitivity of array detector measurements in determining shifts of MLC leaf positions

Shang

Godley

Huang

et al. 2017

J Applied Clin Med Phys

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Using a MatriXX 2D ionization chamber array, we evaluated the detection sensitivity of systematically introduced MLC leaf positioning shifts to test whether the conventional IMRT QA method can be used for quality assurance of an MLC tracking algorithm. Because of finite special resolution, we first tested whether the detection sensitivity was dependent of the locations of leaf shifts and positions of ionization chambers. We then introduced the same systematic leaf shifts in two clinical intensity modulated radiotherapy plans (prostate and head and neck cancer). Our results reported differences between the measured planar doses with and without MLC shifts (errors). Independent of the locations of the leaf position shifts and positions of the detectors, for the simple rectangular fields, the MatriXX was able to detect ±2 mm MLC leaf positioning shifts with Gamma index of 3%/3 mm and ±1 mm MLC leaf position shifts with Gamma index of 2%/2 mm. For the clinical plans, measuring the fields individually, leaf positioning shifts of ±2 mm were detected using Gamma index of 3%/3 mm and a passing rate of 95%. When the fields were measured compositely, the Gamma index exhibited less sensitivity for the detection of leaf positioning shifts than when the fields were measured individually. In conclusion, if more than 2 mm MLC leaf shifts were required, the commercial detector array (MatriXX) is able to detect such MLC positioning shifts, otherwise a more sensitive quality assurance method should be used.

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“…The real-time correlation between these parameters is inevitable during VMAT delivery because any variation generates a potential error [4]. The MLC plays a vital role in VMAT delivery and, thus, any error in the MLC position creates an over-or under-dose during treatment [5]. Considerable differences also exist between the optimization processes of VMAT and IMRT, which complicates VMAT plans.…”

Section: Introductionmentioning

confidence: 99%

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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Direct impact analysis of multi-leaf collimator leaf position errors on dose distributions in volumetric modulated arc therapy: a pass rate calculation between measured planar doses with and without the position errors

Cited by 39 publications

References 13 publications

Is RapidArc more susceptible to delivery uncertainties than dynamic IMRT?

Is RapidArc more susceptible to delivery uncertainties than dynamic IMRT?

Sensitivity of array detector measurements in determining shifts of MLC leaf positions

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

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