Search for IMRT inverse plans with piecewise constant fluence maps using compressed sensing techniques

Zhu, Lei; Li, Xing

doi:10.1118/1.3110163

Cited by 42 publications

(49 citation statements)

References 40 publications

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“…The continuously growing popularity of the use of direct aperture optimization 37 and most recent compressed sensingbased optimization 38,39 suggests that the marker blockage problem will be greatly diminished. Those optimizations lead to a plan with a significant reduction in the number of segments ͑typically around five͒ while maintaining the dosimetric benefits of IMRT.…”

Section: Discussionmentioning

confidence: 99%

Clinical development of a failure detection‐based online repositioning strategy for prostate IMRT—Experiments, simulation, and dosimetry study

et al. 2010

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Purpose: To implement and evaluate clinic-ready adaptive imaging protocols for online patient repositioning ͑motion tracking͒ during prostate IMRT using treatment beam imaging supplemented by minimal, as-needed use of on-board kV. Methods: The authors examine the two-step decision-making strategy: ͑1͒ Use cine-MV imaging and online-updated characterization of prostate motion to detect target motion that is potentially beyond a predefined threshold and ͑2͒ use paired MV-kV 3D localization to determine overthreshold displacement and, if needed, reposition the patient. Two levels of clinical implementation were evaluated: ͑1͒ Field-by-field based motion correction for present-day linacs and ͑2͒ instantaneous repositioning for new-generation linacs with capabilities of simultaneous MV-kV imaging and remote automatic couch control during treatment delivery. Experiments were performed on a Varian Trilogy linac in clinical mode using a 4D motion phantom programed with prostate motion trajectories taken from patient data. Dosimetric impact was examined using a 2D ion chamber array. Simulations were done for 536 trajectories from 17 patients. Results: Despite the loss of marker detection efficiency caused by the MLC leaves sometimes obscuring the field at the marker's projected position on the MV imager, the field-by-field correction halved ͑from 23% to 10%͒ the mean percentage of time that target displacement exceeded a 3 mm threshold, as compared to no intervention. This was achieved at minimal cost in additional imaging ͑average of one MV-kV pair per two to three treatment fractions͒ and with a very small number of repositionings ͑once every four to five fractions͒. Also with low kV usage ͑ϳ2 / fraction͒, the instantaneous repositioning approach reduced overthreshold time by more than 75% ͑23% to 5%͒ even with severe MLC blockage as often encountered in current IMRT and could reduce the overthreshold time tenfold ͑to Ͻ2%͒ if the MLC blockage problem were relieved. The information acquired for repositioning using combined MV-kV images was found to have submillimeter accuracy. Conclusions: This work demonstrated with a current clinical setup that substantial reduction of adverse targeting effects of intrafraction prostate motion can be realized. The proposed adaptive imaging strategy incurs minimal imaging dose to the patient as compared to other stereoscopic imaging techniques.

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Section: Discussionmentioning

confidence: 99%

Clinical development of a failure detection‐based online repositioning strategy for prostate IMRT—Experiments, simulation, and dosimetry study

et al. 2010

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“…On the planning side, IMRT inverse planning with total-variation regularization has been proposed, 22,23 which is capable of dispensing unnecessary segments in intensity modulated beams to produce easily deliverable piece-wise constant fluence maps. The approach is also applicable to treatment with flattening filter free beams.…”

Section: Discussionmentioning

confidence: 99%

“…For each patient, we planned the treatment using Pinnacle TM system (Philips Radiation Oncology Systems, Milpitas, CA), with different numbers of beams (5,7,11,15,23,31,61, and 90 in this study), uniformly distributed in the range of 0 to 360…”

Section: Iia Treatment Planningmentioning

confidence: 99%

Bridging the gap between IMRT and VMAT: Dense angularly sampled and sparse intensity modulated radiation therapy

2011

Medical Physics

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Purpose: To propose an alternative radiation therapy (RT) planning and delivery scheme with optimal angular beam sampling and intrabeam modulation for improved dose distribution while maintaining high delivery efficiency. Methods: In the proposed approach, coined as dense angularly sampled and sparse intensity modulated RT (DASSIM-RT), a large number of beam angles are used to increase the angular sampling, leading to potentially more conformal dose distributions as compared to conventional IMRT. At the same time, intensity modulation of the incident beams is simplified to eliminate the dispensable segments, compensating the increase in delivery time caused by the increased number of beams and facilitating the plan delivery. In a sense, the proposed approach shifts and transforms, in an optimal fashion, some of the beam segments in conventional IMRT to the added beams. For newly available digital accelerators, the DASSIM-RT delivery can be made very efficient by concatenating the beams so that they can be delivered sequentially without operator's intervention. Different from VMAT, the level of intensity modulation in DASSIS-RT is field specific and optimized to meet the need of each beam direction. Three clinical cases (a head and neck (HN) case, a pancreas case, and a lung case) are used to evaluate the proposed RT scheme. DASSIM-RT, VMAT, and conventional IMRT plans are compared quantitatively in terms of the conformality index (CI) and delivery efficiency. Results: Plan quality improves generally with the number and intensity modulation of the incident beams. For a fixed number of beams or fixed level of intensity modulation, the improvement saturates after the intensity modulation or number of beams reaches to a certain level. An interplay between the two variables is observed and the saturation point depends on the values of both variables. For all the cases studied here, the CI of DASSIM-RT with 15 beams and 5 intensity levels (0.90, 0.79, and 0.84 for the HN, pancreas, and lung cases, respectively) is similar with that of conventional IMRT with seven beams and ten intensity levels (0.88, 0.79, and 0.83) and is higher than that of single-arc VMAT (0.75, 0.75, and 0.82). It is also found that the DASSIM-RT plans generally have better sparing of organs-at-risk than IMRT plans. It is estimated that the dose delivery time of DASSIM-RT with 15 beams and 5 intensity levels is about 4.5, 4.4, and 4.2 min for the HN, pancreas, and lung case, respectively, similar to that of IMRT plans with 7 beams and 10 intensity levels. Conclusion: DASSIS-RT bridges the gap between IMRT and VMAT and allows optimal sampling of angular space and intrabeam modulation, thus it provides improved conformity in dose distributions while maintaining high delivery efficiency.

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“…Although the total-variation regularization with quadratic programming (QP) (Ref. 25) was successfully applied to optimize the fluence map in conventional IMRT, [22][23][24] direct application of the method to deal with the DASSIM-RT inverse planning is rather challenging because of the dramatically increased scale of problem. The use of a second-order Newton step in QP for large matrix sizes may significantly lower the convergence speed and, more computationally problematic, requires prohibitively large memory space for the optimization.…”

Section: Introductionmentioning

confidence: 99%

“…Two recent advancements in RT support the applications of DASSIM-RT in clinical practice. On the planning side, IMRT inverse planning with total-variation (TV) regularization [22][23][24] has been proposed, which is capable of dispensing unnecessary segments in intensity modulated beams to produce easily deliverable piecewise constant fluence maps. On the delivery side, DASSIM-RT is made efficient by the high dose-rate beams and by autofield sequencing available on TrueBeam TM , which eliminates the unnecessary operator control of gantry rotation during dose delivery.…”

Section: Introductionmentioning

confidence: 99%

Dose optimization with first‐order total‐variation minimization for dense angularly sampled and sparse intensity modulated radiation therapy (DASSIM‐RT)

Kim

Lee³

et al. 2012

Med. Phys.

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Purpose:A new treatment scheme coined as dense angularly sampled and sparse intensity modulated radiation therapy (DASSIM-RT) has recently been proposed to bridge the gap between IMRT and VMAT. By increasing the angular sampling of radiation beams while eliminating dispensable segments of the incident fields, DASSIM-RT is capable of providing improved conformity in dose distributions while maintaining high delivery efficiency. The fact that DASSIM-RT utilizes a large number of incident beams represents a major computational challenge for the clinical applications of this powerful treatment scheme. The purpose of this work is to provide a practical solution to the DASSIM-RT inverse planning problem. Methods: The inverse planning problem is formulated as a fluence-map optimization problem with total-variation (TV) minimization. A newly released L1-solver, template for first-order conic solver (TFOCS), was adopted in this work. TFOCS achieves faster convergence with less memory usage as compared with conventional quadratic programming (QP) for the TV form through the effective use of conic forms, dual-variable updates, and optimal first-order approaches. As such, it is tailored to specifically address the computational challenges of large-scale optimization in DASSIM-RT inverse planning. Two clinical cases (a prostate and a head and neck case) are used to evaluate the effectiveness and efficiency of the proposed planning technique. DASSIM-RT plans with 15 and 30 beams are compared with conventional IMRT plans with 7 beams in terms of plan quality and delivery efficiency, which are quantified by conformation number (CN), the total number of segments and modulation index, respectively. For optimization efficiency, the QP-based approach was compared with the proposed algorithm for the DASSIM-RT plans with 15 beams for both cases. Results: Plan quality improves with an increasing number of incident beams, while the total number of segments is maintained to be about the same in both cases. For the prostate patient, the conformation number to the target was 0.7509, 0.7565, and 0.7611 with 80 segments for IMRT with 7 beams, and DASSIM-RT with 15 and 30 beams, respectively. For the head and neck (HN) patient with a complicated target shape, conformation numbers of the three treatment plans were 0.7554, 0.7758, and 0.7819 with 75 segments for all beam configurations. With respect to the dose sparing to the critical structures, the organs such as the femoral heads in the prostate case and the brainstem and spinal cord in the HN case were better protected with DASSIM-RT. For both cases, the delivery efficiency has been greatly improved as the beam angular sampling increases with the similar or better conformal dose distribution. Compared with conventional quadratic programming approaches, firstorder TFOCS-based optimization achieves far faster convergence and smaller memory requirements in DASSIM-RT. Conclusions:The new optimization algorithm TFOCS provides a practical and timely solution to the DASSIM-RT or other inverse pla...

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Search for IMRT inverse plans with piecewise constant fluence maps using compressed sensing techniques

Cited by 42 publications

References 40 publications

Clinical development of a failure detection‐based online repositioning strategy for prostate IMRT—Experiments, simulation, and dosimetry study

Clinical development of a failure detection‐based online repositioning strategy for prostate IMRT—Experiments, simulation, and dosimetry study

Bridging the gap between IMRT and VMAT: Dense angularly sampled and sparse intensity modulated radiation therapy

Dose optimization with first‐order total‐variation minimization for dense angularly sampled and sparse intensity modulated radiation therapy (DASSIM‐RT)

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