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

Szpala, Stanislaw; Cao, Fred; Kohli, Kirpal

doi:10.1120/jacmp.v15i2.4484

Cited by 37 publications

(64 citation statements)

References 26 publications

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“…The difference between the measured and optimized DLG values is caused by different contributions to the dose from the beam penumbra, which is a consequence of different patterns of leaf movement. Szpala et al (44) found out that the DLG values are a function of the distance (in the BEV) between the dose point and the leaf ending, and the width of the MLC slit. Therefore, calculation using a single DLG value may overestimate the measurement in the proximal penumbra, while it may underestimate the dose in the distal penumbra for RapidArc delivery (44) .…”

Section: Discussionmentioning

confidence: 99%

“…Szpala et al (44) found out that the DLG values are a function of the distance (in the BEV) between the dose point and the leaf ending, and the width of the MLC slit. Therefore, calculation using a single DLG value may overestimate the measurement in the proximal penumbra, while it may underestimate the dose in the distal penumbra for RapidArc delivery (44) . For IMRT delivery, the DLG values for smaller and larger regions average out and a single value can serve as the optimal value for different widths of the MLC slits (44) .…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, calculation using a single DLG value may overestimate the measurement in the proximal penumbra, while it may underestimate the dose in the distal penumbra for RapidArc delivery (44) . For IMRT delivery, the DLG values for smaller and larger regions average out and a single value can serve as the optimal value for different widths of the MLC slits (44) . Therefore, the DLG values were optimized for RapidArc delivery by evaluating the measured and calculated dose for selected spine radiosurgery cases due to the requirement of an extremely steep dose gradient.…”

Section: Discussionmentioning

confidence: 99%

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Characteristics of a novel treatment system for linear accelerator–based stereotactic radiosurgery

Song

Chin-Snyder

et al. 2015

J Applied Clin Med Phys

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The purpose of this study is to characterize the dosimetric properties and accuracy of a novel treatment platform (Edge radiosurgery system) for localizing and treating patients with frameless, image‐guided stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). Initial measurements of various components of the system, such as a comprehensive assessment of the dosimetric properties of the flattening filter‐free (FFF) beams for both high definition (HD120) MLC and conical cone‐based treatment, positioning accuracy and beam attenuation of a six degree of freedom (6DoF) couch, treatment head leakage test, and integrated end‐to‐end accuracy tests, have been performed. The end‐to‐end test of the system was performed by CT imaging a phantom and registering hidden targets on the treatment couch to determine the localization accuracy of the optical surface monitoring system (OSMS), cone‐beam CT (CBCT), and MV imaging systems, as well as the radiation isocenter targeting accuracy. The deviations between the percent depth‐dose curves acquired on the new linac‐based system (Edge), and the previously published machine with FFF beams (TrueBeam) beyond Dmax were within 1.0% for both energies. The maximum deviation of output factors between the Edge and TrueBeam was 1.6%. The optimized dosimetric leaf gap values, which were fitted using Eclipse dose calculations and measurements based on representative spine radiosurgery plans, were 0.700 mm and 1.000 mm, respectively. For the conical cones, 6X FFF has sharper penumbra ranging from 1.2−1.8 mm (80%‐20%) and 1.9−3.8 mm (90%‐10%) relative to 10X FFF, which has 1.2−2.2 mm and 2.3−5.1 mm, respectively. The relative attenuation measurements of the couch for PA, PA (rails‐in), oblique, oblique (rails‐out), oblique (rails‐in) were: −2.0%, −2.5%, −15.6%, −2.5%, −5.0% for 6X FFF and −1.4%, −1.5%, −12.2%, −2.5%, −5.0% for 10X FFF, respectively, with a slight decrease in attenuation versus field size. The systematic deviation between the OSMS and CBCT was −0.4±0.2 mm, 0.1±0.3 mm, and 0.0±0.1 mm in the vertical, longitudinal, and lateral directions. The mean values and standard deviations of the average deviation and maximum deviation of the daily Winston‐Lutz tests over three months are 0.20±0.03 mm and 0.66±0.18 mm, respectively. Initial testing of this novel system demonstrates the technology to be highly accurate and suitable for frameless, linac‐based SRS and SBRT treatment.PACS number: 87.56.J‐

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Characteristics of a novel treatment system for linear accelerator–based stereotactic radiosurgery

Song

Chin-Snyder

et al. 2015

J Applied Clin Med Phys

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“…(4,12,24,27–38) Many of these publications are particularly applicable for use with Varian linear accelerators that use the Eclipse TPS. In this case, the dose contribution is adjusted by modifying the DLG that is adjusted during linac commissioning to account for differences in the radiation versus light projected field 33 , 36 . Others have developed methods for calibrating and commissioning the rounded leaf ends of the MLCs with the Pinnacle TPS for Elekta linacs with asymmetric jaws, 5 , 34 , 39 , 40 but they do not specifically address leaf gap doses that are not blocked by jaws as in the case for the Elekta beam modulator.…”

Section: Discussionmentioning

confidence: 99%

Rounded leaf end modeling in Pinnacle VMAT treatment planning for fixed jaw linacs

Young

Yang

Cao

et al. 2016

J Applied Clin Med Phys

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During volume‐modulated arc therapies (VMAT), dosimetric errors are introduced by multiple open dynamic leaf gaps that are present in fixed diaphragm linear accelerators. The purpose of this work was to develop a methodology for adjusting the rounded leaf end modeling parameters to improve out‐of‐field dose agreement in SmartArc VMAT treatment plans delivered by fixed jaw linacs where leaf gap dose is not negligible. Leaf gap doses were measured for an Elekta beam modulator linac with 0.4 cm micro‐multileaf collimators (MLC) using an A16 micro‐ionization chamber, a MatriXX ion chamber detector array, and Kodak EDR2 film dosimetry in a solid water phantom. The MLC offset and rounded end tip radius were adjusted in the Pinnacle treatment planning system (TPS) to iteratively arrive at the optimal configuration for 6 MV and 10 MV photon energies. Improvements in gamma index with a 3%/3 mm acceptance criteria and an inclusion threshold of 5% of maximum dose were measured, analyzed, and validated using an ArcCHECK diode detector array for field sizes ranging from 1.6 to 14 cm square field arcs and Task Group (TG) 119 VMAT test cases. The best results were achieved for a rounded leaf tip radius of 13 cm with a 0.1 cm MLC offset. With the optimized MLC model, measured gamma indices ranged between 99.9% and 91.7% for square field arcs with sizes between 3.6 cm and 1.6 cm, with a maximum improvement of 42.7% for the 1.6 cm square field size. Gamma indices improved up to 2.8% in TG‐119 VMAT treatment plans. Imaging and Radiation Oncology Core (IROC) credentialing of a VMAT plan with the head and neck phantom passed with a gamma index of 100%. Fine‐tune adjustments to MLC rounded leaf ends may improve patient‐specific QA pass rates and provide more accurate predictions of dose deposition to avoidance structures.PACS number(s): 87.55.D‐, 87.55.kd, 87.55.kh

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“…Rounded end MLCs suffer from bigger transmission penumbra and higher leaf-end radiation transmission. 9 For the current standard prescription dose to the target, 3DCRT plans usually meet the clinical standards. However, optimal jaw position can help reduce dose to OARs surrounding the target.…”

Section: Introductionmentioning

confidence: 99%

Impact of jaw position on sparing organs at risk in 3-dimensional conformal radiation therapy of pancreatic cancer

Paudel

Narayanasamy

Han

et al. 2016

Int J Cancer Ther Oncol

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Purpose: The objective of this work is to investigate the impact of collimator jaw position on dose to organs at risk (OARs) during a 3-dimensional conformal radiotherapy (3DCRT) of pancreatic cancer and postulate a method to minimize OAR dose by proper positioning of the jaws. Methods: Clinically delivered 3DCRT treatment plans for 10 patients optimized with multiple static beams using multileaf collimator (MLC) leaves conformed to a block margin around target, and collimator jaws aligned with outer extent of the block margin were selected. Subsequent plans were generated by displacing the collimator jaws outward in lateral, superior-inferior or both directions by 1 and 2 cm without altering the MLC position. Computed dose to OARs and target with unaltered dose normalization were compared against the corresponding dose obtained from the original plans. Results: Outward displacement of the collimator jaws by 1 cm in lateral and/or superior-inferior direction resulted in a significant increase in mean dose to the studied OARs. The increase was found to be proportional to the outward displacement of the jaws. The increase in maximum dose to spinal cord was significant in a few patients while it was insignificant for all other OARs. Conclusion: Collimator jaws aligned with outer extent of a block margin minimize dose to OARs. Any gap between the block margin and the collimator jaws can lead to an inadvertent delivery of higher dose to the OARs. Hence, the use of an optimal jaw position during treatment planning becomes important to all patient plans.

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

Cited by 37 publications

References 26 publications

Characteristics of a novel treatment system for linear accelerator–based stereotactic radiosurgery

Characteristics of a novel treatment system for linear accelerator–based stereotactic radiosurgery

Rounded leaf end modeling in Pinnacle VMAT treatment planning for fixed jaw linacs

Impact of jaw position on sparing organs at risk in 3-dimensional conformal radiation therapy of pancreatic cancer

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