Monte Carlo modeling of the ModuLeaf miniature MLC for small field dosimetry and quality assurance of the clinical treatment planning system

Crop, F.; Reynaert, N.; Pittomvils, G.; Paelinck, Leen; Gersem, Werner De; Wagter, Carlos De; Vakaet, Luc; Neve, Wilfried De; Thierens, Hubert

doi:10.1088/0031-9155/52/11/022

Cited by 27 publications

(20 citation statements)

References 54 publications

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“…This is likely due to the larger number of control points needed to specify sliding window plans, but also because the commercial optimization algorithms have tended to direct aperture optimization rather than the two-step fluence map and sequencing approach. Although sliding window delivery typically has smaller fields and can also take longer, due to the finite leaf speed, the problems that arise from this – more challenging dosimetry (Crop et al 2007, Calvo et al 2012) and larger delivery times with more control points – are surmountable, and in our opinion worth tackling due to the promise of superior dose distributions achieved by exact matching of optimal fluence maps (Calvo et al 2012)…”

Section: Discussionmentioning

confidence: 99%

Optimal partial-arcs in VMAT treatment planning

Wala¹,

Salari²,

Chen³

et al. 2012

Phys. Med. Biol.

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Purpose To improve the delivery efficiency of VMAT by extending the recently published VMAT treatment planning algorithm vmerge to automatically generate optimal partial-arc plans. Methods and materials A high-quality initial plan is created by solving a convex multicriteria optimization problem using 180 equi-spaced beams. This initial plan is used to form a set of dose constraints, and a set of partial-arc plans is created by searching the space of all possible partial-arc plans that satisfy these constraints. For each partial-arc, an iterative fluence map merging and sequencing algorithm (vmerge) is used to improve the delivery efficiency. Merging continues as long as the dose quality is maintained above a user-defined threshold. The final plan is selected as the partial-arc with the lowest treatment time. The complete algorithm is called pmerge. Results Partial-arc plans are created using pmerge for a lung, liver and prostate case, with final treatment times of 127, 245 and 147 seconds. Treatment times using full arcs with vmerge are 211, 357 and 178 seconds. The mean doses to the critical structures for the vmerge and pmerge plans are kept within 5% of those in the initial plan, and the target volume covered by the prescription isodose is maintained above 98% for the pmerge and vmerge plans. Additionally, we find that the angular distribution of fluence in the initial plans is predictive of the start and end angles of the optimal partial-arc. Conclusions The pmerge algorithm is an extension to vmerge that automatically finds the partial-arc plan that minimizes the treatment time. VMAT delivery efficiency can be improved by employing partial-arcs without compromising dose quality. Partial-arcs are most applicable to cases with non-centralized targets, where the time savings are greatest.

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Section: Discussionmentioning

confidence: 99%

Optimal partial-arcs in VMAT treatment planning

Wala¹,

Salari²,

Chen³

et al. 2012

Phys. Med. Biol.

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“…Generally, the MC‐based linac head is verified using PDDs and beam profiles for several rectangular fields formed by specifically shaped collimators or variable jaws 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 . On the other hand, the secondary collimator in the Vero4DRT is of a fixed type and the field is formed using the MLC only.…”

Section: Methodsmentioning

confidence: 99%

“…The results of EGSnrc/BEAMnrc simulations of several types of MLCs, such as ModuLeaf MLC, (21) BrainLAB microMLC, (30) Millennium 120, 17 , 18 and HD120MLC, (19) have been reported. BEAMnrc provides a series of component modules (CM) for modeling various types of MLC with ease.…”

Section: Methodsmentioning

confidence: 99%

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Development of a dose verification system for Vero4DRT using Monte Carlo method

Ishihara

Sawada

Nakamura

et al. 2014

J Applied Clin Med Phys

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Vero4DRT is an innovative image‐guided radiotherapy system employing a C‐band X‐ray head with gimbal mechanics. The purposes of this study were to propose specific MC models of the linac head and multileaf collimator (MLC) for the Vero4DRT and to verify their accuracy. For a 6 MV photon beam delivered by the Vero4DRT, a simulation code was implemented using EGSnrc. The linac head model and the MLC model were simulated based on its specification. Next, the percent depth dose (PDD) and beam profiles at depths of 15, 100, and 200 mm were simulated under source‐to‐surface distance of 900 and 1000 mm. Field size was set to 150×150.15emmm2 at a depth of 100 mm. Each of the simulated dosimetric metrics was then compared with the corresponding measurements by a 0.125 cc ionization chamber. After that, intra‐ and interleaf leakage, tongue‐and‐groove, and rounded‐leaf profiles were simulated for the static MLC model. Meanwhile, film measurements were performed using EDR2 films under similar conditions to simulation. The measurement for the rounded‐leaf profile was performed using the water phantom and the ionization chamber. The leaf physical density and abutting leaf gap were adjusted to obtain good agreement between the simulated intra‐ and interleaf leakage profiles and measurements. For the MLC model in step‐and‐shoot cases, a pyramid and a prostate IMRT field were simulated, while film measurements were performed using EDR2. For the linac head, exclusive of MLC, the difference in PDD was <1.0% after the buildup region. The simulated beam profiles agreed to within 1.3% at each depth. The MLC model has been shown to reproduce dose measurements within 2.5% for static tests. The MLC is made of tungsten alloy with a purity of 95%. The leaf gap of 0.015 cm and the MLC physical density of 18.0.15emnormalg/.15emcm3, which provided the best agreement between the simulated and measured leaf leakage, were assigned to our MC model. As a result, the simulated step‐and‐shoot IMRT dose distributions agreed with the film measurements to within 3.3%, with exception of the penumbra region. We have developed specific MC models of the linac head and the MLC in the Vero4DRT system. The results have demonstrated that our MC models have high accuracy.PACS numbers: 87.55.K‐, 87.56.nk, 87.56.bd

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“…• As the beam shape is made smaller, the total photon energy spectrum shifts to a spectrum determined by the thickness of the flattening filter (22,26) • The photon fluence will decrease with smaller fields due to the partial covering of the effective spot size (81) • The photon fluence will decrease with smaller fields due to the scattering in the flattening filter (81)…”

Section: General Remarksmentioning

confidence: 99%