Calculation of absorbed dose distributions from dynamic wedges

Storchi, P.; Woudstra, Evert; Verlinde, P.; Johansson, Karl-Axel; Samuelsson, Anna

doi:10.1088/0031-9155/43/6/009

Cited by 17 publications

(9 citation statements)

References 6 publications

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“…The DW dose calculation (12) uses only open‐field data. Dose distribution is determined by superposition of asymmetric rectangular fields in the wedge direction.…”

Section: Methodsmentioning

confidence: 99%

Comparison between measured and calculated dynamic wedge dose distributions using the anisotropic analytic algorithm and pencil‐beam convolution

Caprile

Venencia

Besa

2007

J Applied Clin Med Phys

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We used the two available calculation algorithms of the Varian Eclipse 7.3 three‐dimensional (3D) treatment planning system (TPS), the anisotropic analytic algorithm (AAA) and pencil‐beam convolution (PBC), to compare measured and calculated two‐dimensional enhanced dynamic wedge (2D EDW) dose distributions, plus implementation of the dynamic wedge into the TPS. Measurements were carried out for a 6‐MV photon beam produced with a Clinac 2300C/D linear accelerator equipped with EDW, using ionization chambers for beam axis measurements and films for dose distributions. Using both algorithms, the calculations were performed by the TPS for symmetric square fields in a perpendicular configuration. Accuracy of the TPS was evaluated using a gamma index, allowing 3% dose variation and 3 mm distance to agreement (DTA) as the individual acceptance criteria. Beam axis wedge factors and percentage depth dose calculation were within 1% deviation between calculated and measured values. In the non‐wedged direction, profiles exhibit variations lower than 2% of dose or 2 mm DTA. In the wedge direction, both algorithms reproduced the measured profiles within the acceptance criteria up to 30 degrees EDW. With larger wedge angles, the difference increased to 3%. The gamma distribution showed that, for field sizes of 10×10 cm or larger, using an EDW of 45 or 60 degrees, the field corners and the high‐dose region of the distribution are not well modeled by PBC. For a 20×20 cm field, using a 60‐degree EDW and PBC for calculation, the percentage of pixels that do not reach the acceptance criteria is 28.5%; but, using the AAA for the same conditions, this percentage is only 0.48% of the total distribution. Therefore, PBC is not reliable for planning a treatment when using a 60‐degree EDW for large field sizes. In all the cases, AAA models wedged dose distributions more accurately than PBC did.PACS numbers: 87.53.Bn, 87.53.Dq, 87.53.Kn

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“…The DW dose calculation (12) uses only open‐field data. Dose distribution is determined by superposition of asymmetric rectangular fields in the wedge direction.…”

Section: Methodsmentioning

confidence: 99%

Comparison between measured and calculated dynamic wedge dose distributions using the anisotropic analytic algorithm and pencil‐beam convolution

Caprile

Venencia

Besa

2007

J Applied Clin Med Phys

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“…Most of the procedures for the implementation of dynamic wedges into a treatment planning system (TPS) presented in the literature are based either on exhaustive measurements (Leavitt et al 1997b) for the acquisition of the necessary dosimetric data, or in a sophisticated modelling of the EDW physics (Desobry et al 1998, Storchi et al 1998, Weber et al 1996.…”

Section: Introductionmentioning

confidence: 99%

The `equivalent wedge' implementation of the Varian Enhanced Dynamic Wedge (EDW) into a treatment planning system

1999

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The purpose of this work was to establish procedures for the implementation of the Varian Enhanced Dynamic Wedge into a treatment planning system (TPS), based as much as possible on simple theoretical considerations and already available data. A method is presented for the calculation (rather than measurement) of off-axis relative wedge transmission curves that are required by the TPS for relative dose calculations. We also present a method for absolute dose (monitor unit) calculations, based on the calculation of an effective wedge factor on the prescription point. A simple formula has been derived for the calculation of the effective wedge factor for the most general case, i.e. an arbitrary effective wedge angle, field size and prescription point. Relative dose calculations have been verified by measurements performed on a Varian Clinac 2300C/D linear accelerator, for 6 MV and 20 MV photon energies. Monitor unit calculations have also been verified experimentally for several cases such as symmetric and asymmetric fields with prescription on the collimator axis or on the geometrical centre of the asymmetric field. The presented technique provides results within 2% for both relative and absolute dose calculations for clinically relevant cases.

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“…Several different methods are available to incorporate the virtual wedge into treatment planning systems, and include commissioning a single, 60°wedge and using a universal wedge approach, commissioning only a limited set of wedge angles, and incorporating the dynamic delivery into the treatment planning system and directly calculating the dose distribution. 6,[19][20][21] Comparing the dynamic wedge implementation described in this report with these other implementations on other vendors' linacs highlights the similarities and differences. The choice to start with the diaphragms open may be viewed as an advantage as far as portal verification goes.…”

Section: Discussionmentioning

confidence: 99%

Dynamic and omni wedge implementation on an Elekta SL linac

2000

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The concommitant use of a multileaf collimator ͑MLC͒ and a wedge can result in conflicts in the optimal collimator angle if both MLC and wedge are fixed relative to one another. This is particularly true of linacs in which a single wedge orientation is provided. In this paper, a solution is provided that makes use of two orthogonal universal wedges ͑omni wedge͒. Although this technique can be applied regardless of the means by which the wedged fields are implemented, the measurements reported in this paper were performed using a fixed, internal mechanical wedge coupled with a dynamic wedge, formed by the motion of one of the backup jaws. An implementation of a dynamic wedge for the Elekta SL series of linear accelerators is presented. Results of measurements of the dosimetric characteristics of both the particular implementation of the dynamic wedge and of the omni field are presented. For the dynamic wedge, measurements were made of the wedge factor and dose profile as a function of field size and depth. In addition, the effects of variables, such as dynamic delivery technique and direction of diaphragm motion, on the dynamic wedge profiles were studied and discussed. For the omni wedge, measurements were made of the degree to which the mathematical formalism for describing an omni wedge matches the measured isodose distributions. Comparisons between mechanical wedge dose distributions and the omni wedge were also made.

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Calculation of absorbed dose distributions from dynamic wedges

Cited by 17 publications

References 6 publications

Comparison between measured and calculated dynamic wedge dose distributions using the anisotropic analytic algorithm and pencil‐beam convolution

Comparison between measured and calculated dynamic wedge dose distributions using the anisotropic analytic algorithm and pencil‐beam convolution

The `equivalent wedge' implementation of the Varian Enhanced Dynamic Wedge (EDW) into a treatment planning system

Dynamic and omni wedge implementation on an Elekta SL linac

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