Optimization of the rounded leaf offset table in modeling the multileaf collimator leaf edge in a commercial treatment planning system

Rice, John R.

doi:10.1120/jacmp.v15i6.4899

Cited by 3 publications

(3 citation statements)

References 9 publications

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“…Rice[ 4 ] used a similar method to optimize the rounded leaf offset table of the MLCi2 in the Philips Pinnacle 3 TPS. Rice's offset table is significantly different from the modified offset table developed in this work.…”

Section: R Esults and Discussionmentioning

confidence: 99%

“…The rounded leaf offset table was measured and modified based on the similar work by Rice. [ 4 ] The radiation field-edge position was measured using an IBA CC13 ionization chamber (IBA Dosimetry GmbH, Schwarzenbruck, Germany) to scan a profile across an 8 cm wide by 40 cm tall opening formed by the MLC banks. The backup jaws were moved to be 1 cm behind the leaf bank (when possible), so they would not impinge on the open field.…”

Section: Aterials and M Ethodsmentioning

confidence: 99%

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Impact of multileaf collimator configuration parameters on the dosimetric accuracy of 6-MV Intensity-Modulated radiation therapy treatment plans

Petersen¹,

Perrin²,

Newhauser³

et al. 2017

J Med Phys

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The purpose of this study was to evaluate the impact of selected configuration parameters that govern multileaf collimator (MLC) transmission and rounded leaf offset in a commercial treatment planning system (TPS) (Pinnacle3, Philips Medical Systems, Andover, MA, USA) on the accuracy of intensity-modulated radiation therapy (IMRT) dose calculation. The MLC leaf transmission factor was modified based on measurements made with ionization chambers. The table of parameters containing rounded-leaf-end offset values was modified by measuring the radiation field edge as a function of leaf bank position with an ionization chamber in a scanning water-tank dosimetry system and comparing the locations to those predicted by the TPS. The modified parameter values were validated by performing IMRT quality assurance (QA) measurements on 19 gantry-static IMRT plans. Planar dose measurements were performed with radiographic film and a diode array (MapCHECK2) and compared to TPS calculated dose distributions using default and modified configuration parameters. Based on measurements, the leaf transmission factor was changed from a default value of 0.001 to 0.005. Surprisingly, this modification resulted in a small but statistically significant worsening of IMRT QA gamma-index passing rate, which revealed that the overall dosimetric accuracy of the TPS depends on multiple configuration parameters in a manner that is coupled and not intuitive because of the commissioning protocol used in our clinic. The rounded leaf offset table had little room for improvement, with the average difference between the default and modified offset values being −0.2 ± 0.7 mm. While our results depend on the current clinical protocols, treatment unit and TPS used, the methodology used in this study is generally applicable. Different clinics could potentially obtain different results and improve their dosimetric accuracy using our approach.

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Section: R Esults and Discussionmentioning

confidence: 99%

Section: Aterials and M Ethodsmentioning

confidence: 99%

Impact of multileaf collimator configuration parameters on the dosimetric accuracy of 6-MV Intensity-Modulated radiation therapy treatment plans

Petersen¹,

Perrin²,

Newhauser³

et al. 2017

J Med Phys

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“…Once a reasonable initial model was created, the MLC X position offset was calibrated. Several methods have been proposed to determine optimal model parameters for the MLC position offset, including comparing films of abutting MLC-defined fields with calculations [15,16] or comparing profiles running parallel to the leaves for fields utilizing a wide range of MLC retracted and over-travel positions [14,17]. In this study, we chose to compare profiles acquired at a depth of 10 cm at 100 cm SSD to the calculations to optimize the MLC X position offset parameters.…”

Section: Mlc Leaf Offset Calibrationmentioning

confidence: 99%

Optimizing beam models for dosimetric accuracy over a wide range of treatments

et al. 2019

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This work presents a systematic approach for testing a dose calculation algorithm over a variety of conditions designed to span the possible range of clinical treatment plans. Using this method, a TrueBeam STx machine with high definition multi-leaf collimators (MLCs) was commissioned in the RayStation treatment planning system (TPS). The initial model parameters values were determined by comparing TPS calculations with standard measured depth dose and profile curves. The MLC leaf offset calibration was determined by comparing measured and calculated field edges utilizing a wide range of MLC retracted and over-travel positions. The radial fluence was adjusted using profiles through both the center and corners of the largest field size, and through measurements of small fields that were located at highly off-axis positions. The flattening filter source was adjusted to improve the TPS agreement for the output of MLC-defined fields with much larger jaw openings. The MLC leaf transmission and leaf end parameters were adjusted to optimize the TPS agreement for highly modulated intensity-modulated radiotherapy (IMRT) plans. The final model was validated for simple open fields, multiple field configurations, the TG 119 C-shape target test, and a battery of clinical IMRT and volumetric-modulated arc therapy (VMAT) plans. The commissioning process detected potential dosimetric errors of over 10% and resulted in a final model that provided in general 3% dosimetric accuracy. This study demonstrates the importance of using a variety of conditions to adjust a beam model and provides an effective framework for achieving high dosimetric accuracy.

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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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Optimization of the rounded leaf offset table in modeling the multileaf collimator leaf edge in a commercial treatment planning system

Cited by 3 publications

References 9 publications

Impact of multileaf collimator configuration parameters on the dosimetric accuracy of 6-MV Intensity-Modulated radiation therapy treatment plans

Impact of multileaf collimator configuration parameters on the dosimetric accuracy of 6-MV Intensity-Modulated radiation therapy treatment plans

Optimizing beam models for dosimetric accuracy over a wide range of treatments

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

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