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

Li, Ruijiang; Li, Xing

doi:10.1118/1.3618736

Cited by 31 publications

(43 citation statements)

References 38 publications

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“…However, the CI from our study was greatly improved, and the mean doses to OAR were lower. In general, highly conformal and homogeneous dose distributions are achievable with VMAT due to its high angular sampling rate of radiation beams [13]. The variation of parameters depends on different weightings and priorities used during planning.…”

Section: Discussionmentioning

confidence: 99%

Volumetric modulated arc therapy planning method for supine craniospinal irradiation

Chen¹,

Chen²,

Atwood³

et al. 2012

J Radiat Oncol

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Background The purpose of this study is to propose a volumetric modulated arc therapy (VMAT) treatment planning technique for supine craniospinal irradiation (CSI) in order to improve dose conformity and homogeneity, as well as the reliability of the matching of abutting fields. Methods and materials CT datasets of a 9-year-old child and a 24-year-old adult treated with supine CSI were identified. The planning target volume (PTV) was contoured to include the whole contents of the brain and spinal canal with a uniform margin of 5 mm. RapidArc plans were generated with two partial arcs covering the brain and the superior portion of the spinal cord and a single partial arc covering the remaining inferior portion of the spinal cord. Conformity and heterogeneity indexes (CI and HI) and organs at risk (OAR) dose-volume histograms were evaluated. The effect of treatment inaccuracy was simulated with intentional patient shifts of ±3 mm. Results The CI for the pediatric and adult cases was 1.0 and 0.99, respectively, and the HI for the two cases was 12.7 and 11.8 %, respectively. The mean dose to the PTV was 102.5 and 102.1 %, respectively, while the mean doses to the OARs were all low. The simulated ±3-mm shift in patient position generated an error of less than ±10 % of the calculated dose in the spinal cord. Conclusions VMAT CSI was able to achieve highly conformal and homogeneous dose distributions, with minor doses to the surrounding normal tissues. Setup errors of ±3 mm were shown to have little effect on the intended dose distribution.

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Section: Discussionmentioning

confidence: 99%

Volumetric modulated arc therapy planning method for supine craniospinal irradiation

Chen¹,

Chen²,

Atwood³

et al. 2012

J Radiat Oncol

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“…On the contrary, current VMAT (with 1-3 arcs) may under-or overmodulate in some or all directions. The concept of dense angularly sampled and sparse intensity modulated radiation therapy (DISSAM-RT), which can be achieved by increasing the angular beam sampling while eliminating dispensable segments of the incident fields, 2 has been introduced to optimally explore a large area of uncharted territory in terms of the number of beams (including noncoplanar and/or nonisocentric beams) and beam modulation. Furthermore, in a recent Point and Counterpoint discussion, 3 we have pointed out that the most general implementation of DASSIM-RT can be described as station parameter optimized radiation therapy (SPORT) in the new age of digital RT.…”

Section: Introductionmentioning

confidence: 99%

An adaptive planning strategy for station parameter optimized radiation therapy (SPORT): Segmentally boosted VMAT

2013

Medical Physics

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Purpose: Conventional volumetric modulated arc therapy (VMAT) discretizes the angular space into equally spaced control points during planning and then optimizes the apertures and weights of the control points. The aperture at an angle in between two control points is obtained through interpolation. This approach tacitly ignores the differential need for intensity modulation of different angles. As such, multiple arcs are often required, which may oversample some angle(s) and undersample others. The purpose of this work is to develop a segmentally boosted VMAT scheme to eliminate the need for multiple arcs in VMAT treatment with improved dose distribution and/or delivery efficiency. Methods: The essence of the new treatment scheme is how to identify the need of individual angles for intensity modulation and to provide the necessary beam intensity modulation for those beam angles that need it. We introduce a "demand metric" at each control point to decide which station or control points need intensity modulation. To boost the modulation at selected stations, additional segments are added in the vicinity of the selected stations. The added segments are then optimized together with the original set of station or control points as a whole. The authors apply the segmentally boosted planning technique to four previously treated clinical cases: two head and neck (HN) cases, one prostate case, and one liver case. The proposed planning technique is compared with conventional one-arc and two-arc VMAT. Results: The proposed segmentally boosted VMAT technique achieves better critical structure sparing than one-arc VMAT with similar or better target coverage in all four clinical cases. The segmentally boosted VMAT also outperforms two-arc VMAT for the two complicated HN cases, yet with ∼30% reduction in the machine monitor units (MUs) relative to two-arc VMAT, which leads to less leakage/scatter dose to the patient and can potentially translate into faster dose delivery. For the less challenging prostate and liver cases, similar critical structure sparing as the two-arc VMAT plans was obtained using the segmentally boosted VMAT. The benefit for the two simpler cases is the reduction of MUs and improvement of treatment delivery efficiency. Conclusions: Segmentally boosted VMAT achieves better dose conformality and/or reduced MUs through effective consideration of the need of individual beam angles for intensity modulation. Elimination of the need for multiple arcs in rotational arc therapy while improving the dose distribution should lead to improved workflow and treatment efficacy, thus may have significant implication to radiation oncology practice.

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“…In many clinical cases, single-arc VMAT may unduly compromise the quality of the dose distribution. 20,21 The use of multiple arcs could be a possible solution to the problem, but it fails to address the need for intensity modulation of each individual beam and may defeat the purpose of fast delivery. VMAT involves gantry rotation during dose delivery and thus requires additional attention in QA.…”

Section: Introductionmentioning

confidence: 99%

“…20 It is achieved by increasing the angular sampling of radiation beams while eliminating dispensable segments of the incident fields. DASSIM-RT combines the desirable features of both VMAT (by increasing the angular sampling) and conventional IMRT (by allowing multiple field specific segments).…”

Section: Introductionmentioning

confidence: 99%

“…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. 20 DASSIM-RT improves conformity in dose distributions while maintaining high delivery efficiency. Hybrids of rotational arc and fixed-gantry dose deliveries and/or treatment with mixed beam energies for different directions are readily achievable with DASSIM-RT.…”

Section: Introductionmentioning

confidence: 99%

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

Cited by 31 publications

References 38 publications

Volumetric modulated arc therapy planning method for supine craniospinal irradiation

Volumetric modulated arc therapy planning method for supine craniospinal irradiation

An adaptive planning strategy for station parameter optimized radiation therapy (SPORT): Segmentally boosted VMAT

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

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