The effects of beamlet size on IMRT optimization

Yi, B; Chen, Y.; Boyer, Arthur L.

doi:10.1007/978-3-642-59758-9_116

Cited by 3 publications

(1 citation statement)

References 2 publications

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“…Supporting this approach is a study demonstrating that the benefit of beamlets smaller than about 5 mmϫ 5 mm is modest. 11 The optimization algorithm is a gradient search algorithm provided by the MatLab optimization toolbox. It is a subspace trust region method based on an interior-reflective Newton method.…”

Section: A Optimization Techniquementioning

confidence: 99%

Simultaneous optimization of sequential IMRT plans

et al. 2005

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Radiotherapy often comprises two phases, in which irradiation of a volume at risk for microscopic disease is followed by a sequential dose escalation to a smaller volume either at a higher risk for microscopic disease or containing only gross disease. This technique is difficult to implement with intensity modulated radiotherapy, as the tolerance doses of critical structures must be respected over the sum of the two plans. Techniques that include an integrated boost have been proposed to address this problem. However, clinical experience with such techniques is limited, and many clinicians are uncomfortable prescribing nonconventional fractionation schemes. To solve this problem, we developed an optimization technique that simultaneously generates sequential initial and boost IMRT plans. We have developed an optimization tool that uses a commercial treatment planning system (TPS) and a high level programming language for technical computing. The tool uses the TPS to calculate the dose deposition coefficients (DDCs) for optimization. The DDCs were imported into external software and the treatment ports duplicated to create the boost plan. The initial, boost, and tolerance doses were specified and used to construct cost functions. The initial and boost plans were optimized simultaneously using a gradient search technique. Following optimization, the fluence maps were exported to the TPS for dose calculation. Seven patients treated using sequential techniques were selected from our clinical database. The initial and boost plans used to treat these patients were developed independently of each other by dividing the tolerance doses proportionally between the initial and boost plans and then iteratively optimizing the plans until a summation that met the treatment goals was obtained. We used the simultaneous optimization technique to generate plans that met the original planning goals. The coverage of the initial and boost target volumes in the simultaneously optimized plans was equivalent to the independently optimized plans actually used for treatment. Tolerance doses of the critical structures were respected for the plan sum; however, the dose to critical structures for the individual initial and boost plans was different between the simultaneously optimized and the independently optimized plans. In conclusion, we have demonstrated a method for optimization of initial and boost plans that treat volume reductions using the same dose per fraction. The method is efficient, as it avoids the iterative approach necessitated by currently available TPSs, and is generalizable to more than two treatment phases. Comparison with clinical plans developed independently suggests that current manual techniques for planning sequential treatments may be suboptimal.

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Section: A Optimization Techniquementioning

confidence: 99%

Simultaneous optimization of sequential IMRT plans

et al. 2005

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Virtual micro‐intensity modulated radiation therapy

Siochi¹

2000

Medical Physics

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Virtual micro‐intensity modulated radiation therapy (VMIMRT) combines a 10×5 mm2 intensity map with a 5×10 mm2 intensity map, delivered at orthogonal collimator settings. The superposition of these component maps (CM) yields a 5×5 mm2 virtual micro‐intensity map (VMIM) that can be delivered with a 1 cm leaf width MLC. A pair of CMs with optimal delivery efficiency and quality must be chosen, since a given VMIM can be delivered using several different pairs. This is possible since, for each group of four VMIM cells that can be covered by an MLC leaf in either collimator orientation, the minimum intensity can be delivered from either collimator setting. By varying the proportions of the minimum values that go into each CM, one can simultaneously minimize the number of potential junction effects and the number of segments required to deliver the VMIM. The minimization is achieved by reducing high leaf direction gradients in the CMs. Several pseudo‐clinical and random VMIMs were studied to determine the applicability of this new technique. A nine level boost map was also studied to investigate dosimetric and spatial resolution issues. Finally, clinical issues for this technique are discussed.

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Delivery of intensity‐modulated radiation therapy with a conventional multileaf collimator: Comparison of dynamic and segmental methods

et al. 2001

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Intensity-modulated radiation therapy (IMRT) can be delivered with a conventional multileaf collimator (MLC), either in dynamic mode (DMLC) or in segmental mode (SMLC, also known as "step-and-shoot"). The advantage of DMLC is its ability to deliver the desired intensity profile produced by inverse planning with a high degree of fidelity. The SMLC method, on the other hand, resembles treatment with multiple static fields, and can be more easily verified. However, the use of SMLC requires that the desired profile be approximated by discrete levels of intensity, which may lead to degradation in the delivered dose distribution. Clearly, the results of SMLC delivery depend on the number of levels and the spatial resolution of the intensity distribution. In this work, we compare the DMLC method and the SMLC method employing different numbers of levels and different spatial resolutions. Three disease sites were studied: prostate, nasopharynx, and breast, with three cases for each. In general, a 5- to 10-level SMLC plan produced results comparable to that from a DMLC plan. The target coverage is improved by increasing the number of levels while critical organs are better protected with finer spatial resolutions. The beam-on-time (MUs) requirement for SMLC was approximately 20% less than DMLC, but the delivery time (in minutes) was about twice as long. Thus, the choice depends on many factors including machine capability, quality assurance, target coverage, critical organ protection, beam-on-time, delivery time, and other clinical considerations.

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The effects of beamlet size on IMRT optimization

Cited by 3 publications

References 2 publications

Simultaneous optimization of sequential IMRT plans

Simultaneous optimization of sequential IMRT plans

Virtual micro‐intensity modulated radiation therapy

Delivery of intensity‐modulated radiation therapy with a conventional multileaf collimator: Comparison of dynamic and segmental methods

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