Dose domain regularization of MLC leaf patterns for highly complex IMRT plans

Nguyen, Dan; O’Connor, Daniel; Yu, Victoria; Ruan, Dan; Cao, Minsong; Low, Daniel A.; Sheng, Ke

doi:10.1118/1.4915286

Cited by 26 publications

(40 citation statements)

References 58 publications

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“…This degree of convergence has been shown to produce plans that are dosimetrically equivalent to other plans that have tighter convergences. 22 A convergence plot for the GBM case is shown in Fig. 1, showing the convergence relative to the optimal value taken at the 10 000th iteration.…”

Section: Resultsmentioning

confidence: 99%

“…When solved using an algorithm based on a proximal-class primal-dual algorithm, the Chambolle-Pock algorithm, 24 we found a new methods, based on L2-norm fidelity terms and L1-norm regularization terms, 22,30 to incorporate fluence maps simplification into the dose domain optimization. In this study, we further developed the methods to solve the VMAT problem, which previously only had greedy heuristic solutions.…”

Section: Discussionmentioning

confidence: 99%

“…Term set 1 is the anisotropic total variation (TV) regularization, which has been shown to successfully encourage piecewise continuity on the fluence maps. 21,22 The TV regularization term considers the entire fluence map of the beam, so the term ultimately controls the segment size and shape, abating irregularities and holes in the aperture shape. Soft regulation of the minimal leaf gap and the max leaf interdigitation can be accomplished by independently adjusting the weightings λ 1 and λ 2 , respectively.…”

Section: A Optimization Formulationmentioning

confidence: 99%

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A comprehensive formulation for volumetric modulated arc therapy planning

et al. 2016

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Purpose: Volumetric modulated arc therapy (VMAT) is a widely employed radiation therapy technique, showing comparable dosimetry to static beam intensity modulated radiation therapy (IMRT) with reduced monitor units and treatment time. However, the current VMAT optimization has various greedy heuristics employed for an empirical solution, which jeopardizes plan consistency and quality. The authors introduce a novel direct aperture optimization method for VMAT to overcome these limitations. Methods: The comprehensive VMAT (comVMAT) planning was formulated as an optimization problem with an L2-norm fidelity term to penalize the difference between the optimized dose and the prescribed dose, as well as an anisotropic total variation term to promote piecewise continuity in the fluence maps, preparing it for direct aperture optimization. A level set function was used to describe the aperture shapes and the difference between aperture shapes at adjacent angles was penalized to control MLC motion range. A proximal-class optimization solver was adopted to solve the large scale optimization problem, and an alternating optimization strategy was implemented to solve the fluence intensity and aperture shapes simultaneously. Single arc comVMAT plans, utilizing 180 beams with 2• angular resolution, were generated for a glioblastoma multiforme case, a lung (LNG) case, and two head and neck cases-one with three PTVs (H&N 3PTV ) and one with foue PTVs (H&N 4PTV )-to test the efficacy. The plans were optimized using an alternating optimization strategy. The plans were compared against the clinical VMAT (clnVMAT) plans utilizing two overlapping coplanar arcs for treatment.Results: The optimization of the comVMAT plans had converged within 600 iterations of the block minimization algorithm. comVMAT plans were able to consistently reduce the dose to all organs-at-risk (OARs) as compared to the clnVMAT plans. On average, comVMAT plans reduced the max and mean OAR dose by 6.59% and 7.45%, respectively, of the prescription dose. Reductions in max dose and mean dose were as high as 14.5 Gy in the LNG case and 15.3 Gy in the H&N 3PTV case. PTV coverages measured by D95, D98, and D99 were within 0.25% of the prescription dose. By comprehensively optimizing all beams, the comVMAT optimizer gained the freedom to allow some selected beams to deliver higher intensities, yielding a dose distribution that resembles a static beam IMRT plan with beam orientation optimization. Conclusions: The novel nongreedy VMAT approach simultaneously optimizes all beams in an arc and then directly generates deliverable apertures. The single arc VMAT approach thus fully utilizes the digital Linac's capability in dose rate and gantry rotation speed modulation. In practice, the new single VMAT algorithm generates plans superior to existing VMAT algorithms utilizing two arcs. C 2016 American Association of Physicists in Medicine. [http://dx

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: A Optimization Formulationmentioning

confidence: 99%

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A comprehensive formulation for volumetric modulated arc therapy planning

et al. 2016

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“…The structures of interest are weighted by the diagonal matrix, W . Term set 2 is the anisotropic total variation regularization on the fluence maps to promote piecewise continuous fluence maps . The matrices, D ∥ and D ⊥ , take derivatives parallel and orthogonal to the MLC leaf direction.…”

Section: Methodsmentioning

confidence: 99%

“…In this study, we aim to overcome the limitations in existing fluence map and direct aperture optimization methods . Instead of incorporating the TV regularization that encourages piecewise smoothness, we incorporate a new regularizer where the fluence map stratification problem is formulated as a piecewise constant segmentation problem.…”

Section: Introductionmentioning

confidence: 99%

Deterministic direct aperture optimization using multiphase piecewise constant segmentation

et al. 2017

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Purpose Direct Aperture Optimization (DAO) attempts to incorporate machine constraints in the inverse optimization to eliminate the post-processing steps in fluence map optimization (FMO) that degrade plan quality. Current commercial DAO methods utilize a stochastic or greedy approach to search a small aperture solution space. In this study, we propose a novel deterministic direct aperture optimization that integrates the segmentation of fluence map in the optimization problem using the multiphase piecewise constant Mumford-Shah formulation. Methods The Mumford-Shah based direct aperture optimization problem was formulated to include an L2-norm dose fidelity term to penalize differences between the projected dose and the prescribed dose, an anisotropic total variation term to promote piecewise continuity in the fluence maps, and the multiphase piecewise constant Mumford-Shah function to partition the fluence into pairwise discrete segments. A proximal-class, first-order primal-dual solver was implemented to solve the large scale optimization problem, and an alternating module strategy was implemented to update fluence and delivery segments. Three patients of varying complexity—one glioblastoma multiforme (GBM) patient, one lung (LNG) patient, and one bilateral head and neck (H&N) patient with 3 PTVs—were selected to test the new DAO method. For each patient, 20 non-coplanar beams were first selected using column generation, followed by the Mumford-Shah based DAO (DAOMS). For comparison, a popular and successful approach to DAO known as simulated annealing—a stochastic approach—was replicated. The simulated annealing DAO (DAOSA) plans were then created using the same beam angles and maximum number of segments per beam. PTV coverage, PTV homogeneity true(D95D5true), and OAR sparing were assessed for each plan. In addition, high dose spillage, defined as the 50% isodose volume divided by the tumor volume, as well as conformity, defined as the van’t Riet conformation number, were evaluated. Results DAOMS achieved essentially the same OAR doses compared with the DAOSA plans for the GBM case. The average difference of OAR Dmax and Dmean between the two plans were within 0.05% of the plan prescription dose. The lung case showed slightly improved critical structure sparing using the DAOMS approach, where the average OAR Dmax and Dmean were reduced by 3.67% and 1.08%, respectively, of the prescription dose. The DAOMS plan substantially improved OAR dose sparing for the H&N patient, where the average OAR Dmax and Dmean were reduced by over 10% of the prescription dose. The DAOMS and DAOSA plans were comparable for the GBM and LNG PTV coverage, while the DAOMS plan substantially improved the H&N PTV coverage, increasing D99 by 6.98% of the prescription dose. For the GBM and LNG patients, the DAOMS and DAOSA plans had comparable high dose spillage but slightly worse conformity with the DAOMS approach. For the H&N plan, DAOMS was considerably superior in high dose spillage and conformity to the DAOSA. The deterministic...

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Fluence smoothing evaluation for whole‐breast automatically generated treatment plans

Zaratim,

Oliveira e Silva,

dos Reis

et al. 2024

J Applied Clin Med Phys

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PurposeThis study aimed to identify the fluence smoothing threshold that preserves the dosimetric quality of planning for breast cancer intensity‐modulated radiation therapy (IMRT).Material and methodsWe conducted automated treatment planning for 60 breast cancer patients using the Eclipse Scripting Application Programming Interface. The plans included four‐field IMRT, emphasizing smoothing weight combinations while maintaining a 4:3 aspect ratio between the X and Y directions. Four weight sets (40 × 30, 100 × 75, 150 × 115.2, and 200 × 150) were tested, resulting in four plans per patient. A total dose of 40.05 Gy over 15 fractions was prescribed. Optimization weigths were dynamically adjusted based on dosimetric evaluations, with the maximum coverage priority set at 200. Statistical analyses were used to assess the dosimetric data.ResultsThe median planning target volume (PTV) coverage varied across smoothing levels, with default smoothing (40 × 30) providing superior median PTV coverage. Lung constraints showed significant differences mainly at higher smoothing levels. Heart constraints exhibited less variation between smoothing levels, with significant differences primarily in the maximum and mean doses for right‐sided patients and between default and higher smoothing levels for left‐sided patients. No significant differences were observed in contralateral breast constraints among all smoothing levels, except at the maximum level for right‐sided patients. Monitor units decreased with increasing smoothing weight, showing significant differences between default and other settings. For right‐sided patients, the median number of monitor units varied from 1346 (40 × 30) to 754 (200 × 150), and for left‐sided patients, from 1333 (40 × 30) to 804 (200 × 150). Chi‐square tests revealed differences in dose constraint adherence between default and maximum smoothing levels, particularly in target coverage.ConclusionOur findings suggest that using a ratio of smoothing weights to target priorities between 1:1.5 and 1:1.6 leads to a favorable balance between complexity and dosimetric plan quality, with no significant impacts on dose constraint adherence.

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Dose domain regularization of MLC leaf patterns for highly complex IMRT plans

Cited by 26 publications

References 58 publications

A comprehensive formulation for volumetric modulated arc therapy planning

A comprehensive formulation for volumetric modulated arc therapy planning

Deterministic direct aperture optimization using multiphase piecewise constant segmentation

Fluence smoothing evaluation for whole‐breast automatically generated treatment plans

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