Clinical dosimetry for implementation of a multileaf collimator

Boyer, Arthur L.; Ochran, Timothy G.; Nyerick, C. E.; Waldron, Timothy J.; Huntzinger, Calvin

doi:10.1118/1.596757

Cited by 120 publications

(78 citation statements)

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“…The y-jaws are strategically placed at the upper and lower borders of the field. Figure 3 et al 25 and Klein et al 26 found that the tertiary MLC design is best treated as a block. That is, the equivalent square of the collimator field size is used.…”

Section: A2a Determination Of Field Size For S Cmentioning

confidence: 99%

Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71

et al. 2014

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A protocol is presented for the calculation of monitor units (MU) for photon and electron beams, delivered with and without beam modifiers, for constant source-surface distance (SSD) and source-axis distance (SAD) setups. This protocol was written by Task Group 71 of the Therapy Physics Committee of the American Association of Physicists in Medicine (AAPM) and has been formally approved by the AAPM for clinical use. The protocol defines the nomenclature for the dosimetric quantities used in these calculations, along with instructions for their determination and measurement. Calculations are made using the dose per MU under normalization conditions, D 0 , that is determined for each user's photon and electron beams. For electron beams, the depth of normalization is taken to be the depth of maximum dose along the central axis for the same field incident on a water phantom at the same SSD, where D 0 = 1 cGy/MU. For photon beams, this task group recommends that a normalization depth of 10 cm be selected, where an energy-dependent D 0 ≤ 1 cGy/MU is required. This recommendation differs from the more common approach of a normalization depth of d m , with D 0 = 1 cGy/MU, although both systems are acceptable within the current protocol. For photon beams, the formalism includes the use of blocked fields, physical or dynamic wedges, and (static) multileaf collimation. No formalism is provided for intensity modulated radiation therapy calculations, although some general considerations and a review of current calculation techniques are included. For electron beams, the formalism provides for calculations at the standard and extended SSDs using either an effective SSD or an air-gap correction factor. Example tables and problems are included to illustrate the basic concepts within the presented formalism.

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Section: A2a Determination Of Field Size For S Cmentioning

confidence: 99%

Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71

et al. 2014

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“…Multileaf collimation (MLC) is standard in all modern linear accelerators used to treat patients 1 , 2 , 3 , 4 , 5 . The importance of rigorous quality assurance, especially with respect to the MLC and its impact on intensity‐modulated radiation therapy (IMRT) delivery, has been emphasized in the literature 6 , 7 , 8 .…”

Section: Introductionmentioning

confidence: 99%

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

Rice

2014

J Applied Clin Med Phys

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An editable rounded leaf offset (RLO) table is provided in the Pinnacle3 treatment planning software. Default tables are provided for major linear accelerator manufacturers, but it is not clear how the default table values should be adjusted by the user to optimize agreement between the calculated leaf tip value and the actual measured value. Since we wish for the calculated MLC‐defined field edge to closely match the actual delivered field edge, optimal RLO table values are crucial. This is especially true for IMRT fields containing a large number of segments, since any errors would add together. A method based on the calculated MLC‐defined field edge was developed for optimizing and modifying the default RLO table values. Modified RLO tables were developed and evaluated for both dosimetric and light field‐based MLC leaf calibrations. It was shown, using a Picket Fence type test, that the optimized RLO table better modeled the calculated leaf tip than the Pinnacle3 default table. This was demonstrated for both an Elekta Synergy 80‐leaf and a Varian 120‐leaf MLC.PACS numbers: 87.55.D‐, 87.55.de, 87.55.Qr

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“…Recently, integrated MLC systems with a 0.5 cm leaf width MLC have become commercially available. Some reports (1,2,3,4,5,6) have addressed the field edge penumbra obtained with 1.0 cm leaf width, compared to secondary collimation and alloy blocking. However the clinical field shaping advantages of the 0.5 cm leaf width over the larger leaf width have not been studied.…”

Section: Introductionmentioning

confidence: 99%

The effect of leaf width and sampling distance on the “stair-stepping” of field borders defined by multileaf collimators

Greer

Beckham

2003

Australas. Phys. Eng. Sci. Med.

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Standard multileaf collimators (MLCs) are now available with 1.0 and 0.5 cm leaf widths. The aim of this work is to compare the dose-undulation and effective penumbra of field edges formed by these MLC leaf widths and to determine how reducing the sampling distance (centre-to-centre distance between adjacent MLC leaves) for the 1.0 cm leaf width compares to the smaller leaf width. The undulation of the 50% isodose line and the 80-20% and 80-30% effective penumbra were compared for a field edge angled at 45q to the MLC leaf motion direction at 8 cm depth. The larger leaf width field was also segmented to form field edges with 0.5, 0.33 and 0.2 cm sampling distance. Random setup variation of 2 mm standard deviation was also incorporated. Dose undulation was 1.5 mm for the 0.5 cm MLC leaf width compared to 4.5 mm for the 1.0 cm width. The 80-20% effective penumbra was 2 mm less for the 0.5 cm leaf width and the 80-30% effective penumbra was ~3 mm less. When random setup variation was incorporated the 0.5 cm leaf width isodoses were straight compared with ~3 mm undulation for the larger MLC. Reducing the sampling distance for the 1.0 cm MLC leaf width to 0.33 cm resulted in penumbra only slightly greater than the 0.5 cm leaf width and removed the undulation. Effective penumbra and dose undulation are reduced for the 0.5 cm leaf width compared to a 1.0 cm leaf width. Reducing the sampling distance for the 1.0 cm MLC leaf can approximate the 0.5 cm leaf width, at the expense of longer treatment times, and increased quality assurance investment.

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Clinical dosimetry for implementation of a multileaf collimator

Cited by 120 publications

References 0 publications

Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71

Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71

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

The effect of leaf width and sampling distance on the “stair-stepping” of field borders defined by multileaf collimators

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