Commissioning measurements on an Elekta Unity MR-Linac

Powers, Marcus; Baines, John; Crane, Robert K.; Fisher, Chantelle; Gibson, S. M.; Marsh, Linda; Oar, Bronwyn; Shoobridge, Ariadne; Simpson‐Page, Emily; Walt, Marchant Van der; Vine, Glenn de

doi:10.1007/s13246-022-01113-7

Cited by 17 publications

(33 citation statements)

References 39 publications

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“…Powers et al . reported that the radiation isocenter was measured using a combination of multiple phantoms and analysis software [ 7 ]. All the results were within 0.5 mm.…”

Section: Resultsmentioning

confidence: 99%

“…and Powers et al . reported TPR 20,10 values of 0.704 and 0.703, respectively [ 6 , 7 ]. The k q factor from IAEA technical reports series 398 was 0.989.…”

Section: Resultsmentioning

confidence: 99%

“…and Powers et al. , respectively [ 6 , 7 ]. In previous works, the calibration was performed at a gantry angle of 90° instead of 0°.…”

Section: Discussionmentioning

confidence: 99%

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Elekta Unity MR-linac commissioning: mechanical and dosimetry tests

Tsuneda

Abe

Fujita

et al. 2022

Journal of Radiation Research

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We report the commissioning results of Elekta Unity for the dosimetric performance and mechanical quality assurance (QA), and propose additional commissioning procedures. Mechanical tests included multi-leaf collimator (MLC) positional accuracy, radiation isocenter diameter at the center and off-center position, and coincidence between the magnetic resonance (MR) image center and radiation isocenter. Comparisons between the measurements and calculations of the simple irradiated field, intensity modulated radiation therapy (IMRT) commissioning, MLC output factor ratio, validation of independent dose calculation software and end-to-end testing were performed to evaluate dosimetric performance. The average values of the MLC positional accuracy for film- and imaging device-based analysis were −0.1 and 0.3 mm, respectively. The measured radiation isocenter size was 0.41 mm, and the off-center results were within 1 mm. The coincidence was −0.21, −1.19 and 0.49 mm along the x-, y- and z-axes, respectively. The calculated percent depth doses (PDD) and profiles agreed with the measurements. The results of independent dose calculation were within the action level recommended by American Associations of Physicist in Medicine. The gamma passing rate (GPR) for IMRT commissioning was 98.6 ± 0.9%, and end-to-end testing of adapted plans showed agreement within 2% between the measurement and calculation. We reported the results of mechanical and dosimetric performances of Elekta Unity, and proposed novel commissioning procedures. Our results should provide knowledge to the physics community for enhancing the QA programs.

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“…Powers et al . reported that the radiation isocenter was measured using a combination of multiple phantoms and analysis software [ 7 ]. All the results were within 0.5 mm.…”

Section: Resultsmentioning

confidence: 99%

“…and Powers et al . reported TPR 20,10 values of 0.704 and 0.703, respectively [ 6 , 7 ]. The k q factor from IAEA technical reports series 398 was 0.989.…”

Section: Resultsmentioning

confidence: 99%

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Elekta Unity MR-linac commissioning: mechanical and dosimetry tests

Tsuneda

Abe

Fujita

et al. 2022

Journal of Radiation Research

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“…It is advised to consult the vendor recommendations on calibration set up. The Unity has been reported to be calibrated under isocentric conditions to deliver: 1 cGy/MU at 10 cm depth and SSD = 133.5 cm [ 59 ] 69.6 cGy per 100 MU, which was the percentage depth dose at 10 cm and resulted in a calibration equivalent to 1 cGy/MU at at the beam quality of the measured system [ 60 ] 1 cGy/MU at 5 cm depth and SSD = 138.5 cm [ 61 ] …”

Section: Reference Dosimetrymentioning

confidence: 99%

“…It should also be noted that beam calibration for Unity systems was previously performed at a gantry angle of 90° or 270° in order to minimise the effect of varying cryostat liquid helium fill levels on attenuation at gantry 0° [, , 59 – 61 ]. When measuring beam output through the side of a water tank, the equivalent thickness of the water tank must be accounted for.…”

Section: Reference Dosimetrymentioning

confidence: 99%

ACPSEM position paper: dosimetry for magnetic resonance imaging linear accelerators

et al. 2023

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Consistency and clear guidelines on dosimetry are essential for accurate and precise dosimetry, to ensure the best patient outcomes and to allow direct dose comparison across different centres. Magnetic Resonance Imaging Linac (MRI-linac) systems have recently been introduced to Australasian clinics. This report provides recommendations on reference dosimetry measurements for MRI-linacs on behalf of the Australiasian College of Physical Scientists and Engineers in Medicine (ACPSEM) MRI-linac working group. There are two configurations considered for MRI-linacs, perpendicular and parallel, referring to the relative direction of the magnetic field and radiation beam, with different impacts on dose deposition in a medium. These recommendations focus on ion chambers which are most commonly used in the clinic for reference dosimetry. Water phantoms must be MR safe or conditional and practical limitations on phantom set-up must be considered. Solid phantoms are not advised for reference dosimetry. For reference dosimetry, IAEA TRS-398 recommendations cannot be followed completely due to physical differences between conventional linac and MRI-linac systems. Manufacturers’ advice on reference conditions should be followed. Beam quality specification of TPR20,10 is recommended. The configuration of the central axis of the ion chamber relative to the magnetic field and radiation beam impacts the chamber response and must be considered carefully. Recommended corrections to delivered dose are $${k}_{{Q}_{msr}{Q}_{0}}^{{f}_{msr}{f}_{ref}}$$ k Q msr Q 0 f msr f ref , a correction for beam quality and $${k}_{\overrightarrow{B},{Q}_{msr}}^{{f}_{msr}}$$ k B → , Q msr f msr , for the impact of the magnetic field on dosimeter response in the magnetic field. Literature based values for $${k}_{\overrightarrow{B},{Q}_{msr}}^{{f}_{msr}}$$ k B → , Q msr f msr are given. It is important to note that this is a developing field and these recommendations should be used together with a review of current literature.

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Is it necessary to perform measurement‐based patient‐specific quality assurance for online adaptive radiotherapy with Elekta Unity MR‐Linac?

Xu,

Xia,

Ren

et al. 2023

J Applied Clin Med Phys

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This study aimed to investigate the necessity of measurement‐based patient‐specific quality assurance (PSQA) for online adaptive radiotherapy by analyzing measurement‐based PSQA results and calculation‐based 3D independent dose verification results with Elekta Unity MR‐Linac.There are two workflows for Elekta Unity enabled in the treatment planning system: adapt to position (ATP) and adapt to shape (ATS). ATP plans are those which have relatively slighter shifts from reference plans by adjusting beam shapes or weights, whereas ATS plans are the new plans optimized from the beginning with probable re‐contouring targets and organs‐at‐risk. PSQA gamma passing rates were measured using an MR‐compatible ArcCHECK diode array for 78 reference plans and corresponding 208 adaptive plans (129 ATP plans and 79 ATS plans) of Elekta Unity. Subsequently, the relationships between ATP, or ATS plans and reference plans were evaluated separately. The Pearson's r correlation coefficients between ATP or ATS adaptive plans and corresponding reference plans were also characterized using regression analysis. Moreover, the Bland–Altman plot method was used to describe the agreement of PSQA results between ATP or ATS adaptive plans and reference plans. Additionally, Monte Carlo‐based independent dose verification software ArcherQA was used to perform secondary dose check for adaptive plans.For ArcCHECK measurements, the average gamma passing rates (ArcCHECK vs. TPS) of PSQA (3%/2 mm criterion) were 99.51% ± 0.88% and 99.43% ± 0.54% for ATP and ATS plans, respectively, which were higher than the corresponding reference plans 99.34% ± 1.04% (p < 0.05) and 99.20% ± 0.71% (p < 0.05), respectively. The Pearson's r correlation coefficients were 0.720 between ATP and reference plans and 0.300 between ATS and reference plans with ArcCHECK, respectively. Furthermore, >95% of data points of differences between both ATP and ATS plans and reference plans were within ±2σ (standard deviation) of the mean difference between adaptive and reference plans with ArcCHECK measurements. With ArcherQA calculation, the average gamma passing rates (ArcherQA vs. TPS) were 98.23% ± 1.64% and 98.15% ± 1.07% for ATP and ATS adaptive plans, separately.It might be unnecessary to perform measurement‐based PSQA for both ATP and ATS adaptive plans for Unity if the gamma passing rates of both measurements of corresponding reference plans and independent dose verification of adaptive plans have high gamma passing rates. Periodic machine QA and verification of adaptive plans were recommended to ensure treatment safety.

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Commissioning measurements on an Elekta Unity MR-Linac

Cited by 17 publications

References 39 publications

Elekta Unity MR-linac commissioning: mechanical and dosimetry tests

Elekta Unity MR-linac commissioning: mechanical and dosimetry tests

ACPSEM position paper: dosimetry for magnetic resonance imaging linear accelerators

Is it necessary to perform measurement‐based patient‐specific quality assurance for online adaptive radiotherapy with Elekta Unity MR‐Linac?

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