Monitor unit settings for intensity modulated beams delivered using a step‐and‐shoot approach

Sharpe, Michael B.; Miller, Brett; Yan, Di; Wong, John W.

doi:10.1118/1.1328383

Cited by 69 publications

(53 citation statements)

References 23 publications

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“…The gamma passing rates were greater than 99% for all of the gating windows and energies using 1 mm and 2% criteria. These findings were comparable to those obtained using a step‐and‐shoot delivery technique 13. However, with stricter agreement criteria of 1%/1mm, the gamma score decreased slightly to 97.66% (Table 2) for 6 MV and ~92% for 10 MV and 18 MV.…”

Section: Resultssupporting

confidence: 82%

See 1 more Smart Citation

Does gated beam delivery impact delivery accuracy on an Elekta linac?

Jermoumi¹,

Xie²,

Cao³

et al. 2017

J Applied Clin Med Phys

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In this study, we evaluated the performance of an Elekta linac in the delivery of gated radiotherapy. Delivery accuracy was examined with an emphasis on the impact of using short gating windows (low monitor unit beam‐on segments) or long beam hold times. The performance was assessed using a 20cm by 20cm open field with the radiation delivered using a range of beam‐on and beam‐off time periods. Gated delivery measurements were also performed for two SBRT plans delivered using volumetric modulated arc therapy (VMAT). Tests included both free‐breathing based gating (covering a variety of gating windows) and simulated breath‐hold based gating. An IBA MatriXX 2D ion chamber array was used for data collection, and the gating accuracy at low MU was evaluated using gamma passing rates. For the 20 cm by 20 cm open field, the measurements generally showed close agreement between the gated and non‐gated beam deliveries. Discrepancies, however, began to appear with a 5‐to‐1 ratio of the beam‐off to beam‐on times. The discrepancies observed for these tight gating windows can be attributed to the small number of monitor units delivered during each beam‐on segment. Dose distribution analysis from the delivery of the two SBRT plans showed gamma passing rates (± 1%, 2%/1 mm) in the range of 95% to 100% for gating windows of 25%, 38%, 50%, 63%, 75%, and 83%. Using a simulated sinusoidal breathing signal with a 4 second period, the gamma passing rate of free‐breathing gating and breath‐hold gating deliveries were measured in the range of 95.7% to 100%. In conclusion, the results demonstrate that Elekta linacs can accurately deliver respiratory gated treatments for both free‐breathing and breath‐hold patients. Some caution should be exercised with the use of very tight gating windows.

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Section: Resultssupporting

confidence: 82%

“…When commissioning a system for gated radiotherapy, it is important to characterize the startup characteristics of the accelerator 13. This is true because gated radiotherapy introduces delivery situations not typically encountered in external beam radiotherapy.…”

Section: Introductionmentioning

confidence: 99%

Does gated beam delivery impact delivery accuracy on an Elekta linac?

Jermoumi¹,

Xie²,

Cao³

et al. 2017

J Applied Clin Med Phys

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show abstract

“…Our results lie within the recommended levels. Several authors have reported the dosimetric characteristics of linear accelerator therapy systems at low MU settings [9]- [14]. Das et al reported dose errors higher than 20% for the first few MUs, which stabilize within 5% at MUs exceeding 10 [10].…”

Section: Discussionmentioning

confidence: 99%

“…As DMLC and VMAT are unavailable in the current commercial version of Vero4DRT, the system should be operated in the step-and-shoot IMRT mode. In previous reports, when step-and-shoot IMRT was implemented with several low monitor units (MUs) per segment at high dose rates, the dosimetric errors were large [9]- [14]. Among researchers who investigated the beam characteristics at low MU settings, Das et al reported a dosimetric error exceeding 20% [10], and Ravikumar et al measured the deviation in dose delivery as 20% -25% (using 6 and 18 MV photon beams at low MU setting) [11].…”

Section: Introductionmentioning

confidence: 99%

Beam Characteristics at Low Dose Monitor Unit Settings for Vero4DRT

Miura¹,

Ozawa²,

Tsuda³

et al. 2015

IJMPCERO

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The stability of delivery of low monitor unit (MU) setting is important especially for step-andshoot intensity-modulated radiotherapy (IMRT), because the nature of the technique is inherent to repeat beam on/off according to the number of the segments. This study evaluates the dose linearity and profile flatness/symmetry under low MU settings for Vero4DRT, a new linear-accelerator based irradiation system that currently implements step-and-shoot IMRT. To evaluate the dose linearity and flatness/symmetry, the point doses and beam profiles were measured as functions of MU and dose rates. The accuracy of dose delivery depended on the dose rate. Under all dose rates, the dose was linear within 1% above 5 MU and within 2% above 3 MU. The beam symmetry was degraded in-line compared with crossline, although both profiles were symmetric within 2% at all dose settings. The profile flatness was also within 2% above 5 MU at any dose rate and showed no significant variation among the low MU settings. To ensure stable beam delivery without increasing the treatment time of Vero4DRT, we recommend a delivery of 5 MU per segment at a dose rate of 500 MU/min.

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“…( 14 – 16 ) This is because the step‐and‐shoot technique sometimes uses so many small sized segments with associated monitor units (MUs). ( 17 , 18 ) Moreover, the delivered dose accuracy can be affected by the accuracy of the leaf positioning, (19) the overshoot effect, (20) and dose nonlinearity for small MU delivery (21) . With more and more external treatment‐planning systems and LINAC support of IMRT delivery using the sliding window technique, more studies regarding the dosimetry and mechanical modulation such as the leaf speed are needed.…”

Section: Introductionmentioning

confidence: 99%

SWIMRT: A graphical user interface using the sliding window algorithm to construct a fluence map machine file

Chow

Григоров

Yazdani

2006

J Applied Clin Med Phys

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A custom‐made computer program, SWIMRT, to construct “multileaf collimator (MLC) machine” file for intensity‐modulated radiotherapy (IMRT) fluence maps was developed using MATLAB® and the sliding window algorithm. The user can either import a fluence map with a graphical file format created by an external treatment‐planning system such as Pinnacle3 or create his or her own fluence map using the matrix editor in the program. Through comprehensive calibrations of the dose and the dimension of the imported fluence field, the user can use associated image‐processing tools such as field resizing and edge trimming to modify the imported map. When the processed fluence map is suitable, a “MLC machine” file is generated for our Varian 21 EX linear accelerator with a 120‐leaf Millennium MLC. This machine file is transferred to the MLC console of the LINAC to control the continuous motions of the leaves during beam irradiation. An IMRT field is then irradiated with the 2D intensity profiles, and the irradiated profiles are compared to the imported or modified fluence map. This program was verified and tested using film dosimetry to address the following uncertainties: (1) the mechanical limitation due to the leaf width and maximum traveling speed, and (2) the dosimetric limitation due to the leaf leakage/transmission and penumbra effect. Because the fluence map can be edited, resized, and processed according to the requirement of a study, SWIMRT is essential in studying and investigating the IMRT technique using the sliding window algorithm. Using this program, future work on the algorithm may include redistributing the time space between segmental fields to enhance the fluence resolution, and readjusting the timing of each leaf during delivery to avoid small fields. Possible clinical utilities and examples for SWIMRT are given in this paper.PACS numbers: 87.53.Kn, 87.53.St, 87.53.Uv

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Monitor unit settings for intensity modulated beams delivered using a step‐and‐shoot approach

Cited by 69 publications

References 23 publications

Does gated beam delivery impact delivery accuracy on an Elekta linac?

Does gated beam delivery impact delivery accuracy on an Elekta linac?

Beam Characteristics at Low Dose Monitor Unit Settings for Vero4DRT

SWIMRT: A graphical user interface using the sliding window algorithm to construct a fluence map machine file

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