Dose-based optimisation for multi-leaf collimator tracking during radiation therapy

Mejnertsen, L.; Hewson, Emily; Nguyen, Doan Trang; Booth, Jeremy; Keall, P.

doi:10.1088/1361-6560/abe836

Cited by 5 publications

(7 citation statements)

References 39 publications

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“…While monitoring the geometric error in real‐time provides some measure of the accuracy of the treatment delivery, it is not directly correlated with the dosimetric error. Real‐time motion‐induced dose error monitoring 25 and its adaptation 48 , 49 will be beneficial to eliminate any significant dose error arising due to intrafraction tumor movements.…”

Section: Discussionmentioning

confidence: 99%

The dosimetric error due to uncorrected tumor rotation during real‐time adaptive prostate stereotactic body radiation therapy

et al. 2022

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Background During prostate stereotactic body radiation therapy (SBRT), prostate tumor translational motion may deteriorate the planned dose distribution. Most of the major advances in motion management to date have focused on correcting this one aspect of the tumor motion, translation. However, large prostate rotation up to 30° has been measured. As the technological innovation evolves toward delivering increasingly precise radiotherapy, it is important to quantify the clinical benefit of translational and rotational motion correction over translational motion correction alone. Purpose The purpose of this work was to quantify the dosimetric impact of intrafractional dynamic rotation of the prostate measured with a six degrees‐of‐freedom tumor motion monitoring technology. Methods The delivered dose was reconstructed including (a) translational and rotational motion and (b) only translational motion of the tumor for 32 prostate cancer patients recruited on a 5‐fraction prostate SBRT clinical trial. Patients on the trial received 7.25 Gy in a treatment fraction. A 5 mm clinical target volume (CTV) to planning target volume (PTV) margin was applied in all directions except the posterior direction where a 3 mm expansion was used. Prostate intrafractional translational motion was managed using a gating strategy, and any translation above the gating threshold was corrected by applying an equivalent couch shift. The residual translational motion is denoted as Tres$T_{res}$. Prostate intrafractional rotational motion Runcorr$R_{uncorr}$ was recorded but not corrected. The dose differences from the planned dose due to Tres$T_{res}$ + Runcorr$R_{uncorr}$, ΔD(Tres$T_{res}$ + Runcorr$R_{uncorr}$) and due to Tres$T_{res}$ alone, ΔD(Tres$T_{res}$), were then determined for CTV D98, PTV D95, bladder V6Gy, and rectum V6Gy. The residual dose error due to uncorrected rotation, Runcorr$R_{uncorr}$ was then quantified: normalΔDResidual$\Delta D_{Residual}$ = ΔD(Tres$T_{res}$ + Runcorr$R_{uncorr}$) ‐ ΔD(Tres${T}_{\textit{res}}$). Results Fractional data analysis shows that the dose differences from the plan (both ΔD(Tres$T_{res}$ + Runcorr$R_{uncorr}$) and ΔD(Tres$T_{res}$)) for CTV D98 was less than 5% in all treatment fractions. ΔD(Tres$T_{res}$ + Runcorr$R_{uncorr}$) was larger than 5% in one fraction for PTV D95, in one fraction for bladder V6Gy, and in five fractions for rectum V6Gy. Uncorrected rotation, Runcorr$R_{uncorr}$ induced residual dose error, normalΔDResidual$\Delta D_{Residual}$, resulted in less dose to CTV and PTV in 43% and 59% treatment fractions, respectively, and more dose to bladder and rectum in 51% and 53% treatment fractions, respectively. The cumulative dose over five fractions, ∑D(Tres$T_{res}$ + Runcorr$R_{uncorr}$) and ∑D(Tres$T_{res}$), was always within 5% of the planned dose for all four structures for every patient. Conclusions The dosimetric impact of tumor rotation on a large prostate cancer patient cohort was quantified in this study. These results suggest that the standard 3–5 mm CTV‐PT...

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Section: Discussionmentioning

confidence: 99%

The dosimetric error due to uncorrected tumor rotation during real‐time adaptive prostate stereotactic body radiation therapy

et al. 2022

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“…We plan for 36. 25 Gy prescribed dose to the PTV (prostate), 34 Gy upper dose constraints in the OARs (bladder and rectum), and 40.5 Gy upper dose constraint in the PTV. Additionally, we introduce shells around the PTV at 3 and 9 mm distance to control dose in normal tissue.…”

Section: Methodsmentioning

confidence: 99%

“…[22][23][24] Similarly, Mejnertsen et al show dose optimization with a simplified dose calculation algorithm for VMAT treatment. 25 However, the particular properties of robotic SBRT including the large number of beam angles make adaptation of these methods challenging. Additionally to the larger number of delivered beams, dose delivery in robotic SBRT is more heterogeneous over time.…”

Section: Introductionmentioning

confidence: 99%

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Towards fast adaptive replanning by constrained reoptimization for intra‐fractional non‐periodic motion during robotic SBRT

Gerlach

Hofmann²,

Fürweger³

et al. 2023

Medical Physics

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Background Periodic and slow target motion is tracked by synchronous motion of the treatment beams in robotic stereotactic body radiation therapy (SBRT). However, spontaneous, non‐periodic displacement or drift of the target may completely change the treatment geometry. Simple motion compensation is not sufficient to guarantee the best possible treatment, since relative motion between the target and organs at risk (OARs) can cause substantial deviations of dose in the OARs. This is especially evident when considering the temporally heterogeneous dose delivery by many focused beams which is typical for robotic SBRT. Instead, a reoptimization of the remaining treatment plan after a large target motion during the treatment could potentially reduce the actually delivered dose to OARs and improve target coverage. This reoptimization task, however, is challenging due to time constraints and limited human supervision. Purpose To study the detrimental effect of spontaneous target motion relative to surrounding OARs on the delivered dose distribution and to analyze how intra‐fractional constrained replanning could improve motion compensated robotic SBRT of the prostate. Methods We solve the inverse planning problem by optimizing a linear program. When considering intra‐fractional target motion resulting in a change of geometry, we adapt the linear program to account for the changed dose coefficients and delivered dose. We reduce the problem size by only reweighting beams from the reference treatment plan without motion. For evaluation we simulate target motion and compare our approach for intra‐fractional replanning to the conventional compensation by synchronous beam motion. Results are generated retrospectively on data of 50 patients. Results Our results show that reoptimization can on average retain or improve coverage in case of target motion compared to the reference plan without motion. Compared to the conventional compensation, coverage is improved from 87.83 % to 94.81 % for large target motion. Our approach for reoptimization ensures fixed upper constraints on the dose even after motion, enabling safer intra‐fraction adaption, compared to conventional motion compensation where overdosage in OARs can lead to 21.79 % higher maximum dose than planned. With an average reoptimization time of 6 s for 200 reoptimized beams our approach shows promising performance for intra‐fractional application. Conclusions We show that intra‐fractional constrained reoptimization for adaption to target motion can improve coverage compared to the conventional approach of beam translation while ensuring that upper dose constraints on VOIs are not violated.

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“…To address the limitations of the previous MLC tracking algorithm, a novel MLC tracking method that optimises the adapted leaf positions to the 3D dose in real-time was developed by Mejnertsen et al (2021). This dose-optimised MLC tracking method incorporates a real-time 3D dose accumulation method to calculate the MLC leaf positions that correct for motion, as well as the dosimetric errors that occur throughout a treatment.…”

Section: Introductionmentioning

confidence: 99%

Optimising multi-target multileaf collimator tracking using real-time dose for locally advanced prostate cancer patients

Hewson¹,

Nguyen²,

Le³

et al. 2022

Phys. Med. Biol.

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Objective: The accuracy of radiotherapy for patients with locally advanced cancer is compromised by independent motion of multiple targets. To date MLC tracking approaches have used 2D geometric optimisation, where the MLC aperture shape is simply translated to correspond to the target’s motion, which results in sub-optimal delivered dose. To address this limitation, a dose-optimised multi-target MLC tracking method was developed and evaluated through simulated locally advanced prostate cancer treatments. Approach: A dose-optimised multi-target tracking algorithm that adapts the MLC aperture to minimise 3D dosimetric error was developed for moving prostate and static lymph node targets. A fast dose calculation algorithm accumulated the planned dose to the prostate and lymph node volumes during treatment in real time, and the MLC apertures were recalculated to minimise the difference between the delivered and planned dose with the included motion. Dose-optimised tracking was evaluated by simulating five locally advanced prostate plans and three prostate motion traces with a relative interfraction displacement. The same simulations were performed using geometric-optimised tracking and no tracking. The dose-optimised, geometric-optimised, and no-tracking results were compared with the planned doses using a 2%/2mm γ criterion. Main Results: The mean dosimetric error was lowest for dose-optimised MLC tracking, with γ-failure rates of 12%±8.5% for the prostate and 2.2%±3.2% for the nodes. The γ-failure rates for geometric-optimised MLC tracking were 23%±12% for the prostate and 3.6%±2.5% for the nodes. When no tracking was used, the γ-failure rates were 37%±28% for the prostate and 24%±3.2% for the nodes. Significance: This study developed a dose-optimised multi-target MLC tracking method that minimises the difference between the planned and delivered doses in the presence of intrafraction motion. When applied to locally advanced prostate cancer, dose-optimised tracking showed smaller errors than geometric-optimised tracking and no tracking for both the prostate and nodes.

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Dose-based optimisation for multi-leaf collimator tracking during radiation therapy

Cited by 5 publications

References 39 publications

The dosimetric error due to uncorrected tumor rotation during real‐time adaptive prostate stereotactic body radiation therapy

The dosimetric error due to uncorrected tumor rotation during real‐time adaptive prostate stereotactic body radiation therapy

Towards fast adaptive replanning by constrained reoptimization for intra‐fractional non‐periodic motion during robotic SBRT

Optimising multi-target multileaf collimator tracking using real-time dose for locally advanced prostate cancer patients

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