Commissioning of a micro multi-leaf collimator and planning system for stereotactic radiosurgery

Micro‐multileaf collimator systems coupled to linear accelerators for radioneurosurgery treatments require a rigorous dosimetric characterization in order to be used in 3D conformal and intensity modulated stereotactic radiosurgery and radiotherapy applications. This characterization involves high precision measurements of leaf transmission, leakage and beam penumbra through the collimation system and requires the use of detectors with high spatial resolution, high sensitivity and practically no energy dependence. In this work the use of GafChromic EBT radiochromic film to measure the basic dosimetric properties of the m3‐mMLC (BrainLAB, Germany) micro‐multileaf collimator system integrated to a 6 MV linear accelerator, is reported. Results show that average values of transmission and leakage radiation are 0.93±0.05% and 1.08±0.08%, respectively. The 80–20% beam penumbra were found to be 2.26±0.11 mm along the leaf side (perpendicular to leaf motion) and 2.31±0.11 mm along the leaf end (parallel to leaf motion) using square field sizes ranging from 9.1 to 1.8 cm. These measurements are in agreement with values reported in the literature for the same type of mMLC using different radiation detectors.PACS number: 87.56.N‐

“…Along the leaf end these values were 2.22 and 2.41 mm for the

9.1 \times 9.1

and

8.0 \times 8.0 {cm}^{2}

Section: Discussioncontrasting

confidence: 72%

Section: Introductionmentioning

confidence: 99%

Radiation transmission, leakage and beam penumbra measurements of a micro‐multileaf collimator using GafChromic EBT film

García‐Garduño

Celis

Lárraga‐Gutiérrez

et al. 2008

“…1 should be equal to arctan (5/100), or 2.9°. This contradicts the 1.8° value presented by Belec et al ( 21 ) but compares favorably to approximately 3° quoted by Cosgrove et al ( 1 ) …”

Section: Methodscontrasting

confidence: 91%

“…1). Cosgrove et al ( 1 ) explained how the leaves are focused towards the target; the central ray is parallel to the vertical edge with the leaf at isocenter, and to the slanted edges when the leaf is extended to

- 5 cm

or retracted to

+ 5 cm

. For the edges to line up with the central ray under these conditions, the slant angle Θ in Fig.…”

Section: Methodsmentioning

confidence: 99%

“…It has many attractive features such as a high definition micro‐MLC (mMLC), ( 1 ) robotic table with six degrees of freedom, ( 2 ) and a robust combination of a flat‐panel X‐ray stereoscopic imaging system and an infrared tracking system for patient positioning. ( 3 ) Several researches have reported overall submillimeter targeting accuracy of the Novalis delivery process in phantoms.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Validation of Pinnacle treatment planning system for use with Novalis delivery unit

Faygelman

Hunt

Walker

et al. 2010

For an institution that already owns the licenses, it is economically advantageous and technically feasible to use Pinnacle TPS (Philips Radiation Oncology Systems, Fitchburg, WI) with the BrainLab Novalis delivery system (BrainLAB A.G., Heimstetten, Germany). This takes advantage of the improved accuracy of the convolution algorithm in the presence of heterogeneities compared with the pencil beam calculation, which is particularly significant for lung SBRT treatments. The reference patient positioning DRRs still have to be generated by the BrainLab software from the CT images and isocenter coordinates transferred from Pinnacle. We validated this process with the end‐to‐end hidden target test, which showed an isocenter positioning error within one standard deviation from the previously established mean value. The Novalis treatment table attenuation is substantial (up to 6.2% for a beam directed straight up and up to 8.4% for oblique incidence) and has to be accounted for in calculations. A simple single‐contour treatment table model was developed, resulting in mean differences between the measured and calculated attenuation factors of 0.0%–0.2%, depending on the field size. The maximum difference for a single incidence angle is 1.1%. The BrainLab micro‐MLC (mMLC) leaf tip, although not geometrically round, can be represented in Pinnacle by an arch with satisfactory dosimetric accuracy. Subsequently, step‐and‐shoot (direct machine parameter optimization) IMRT dosimetric agreement is excellent. VMAT (called “SmartArc” in Pinnacle) treatments with constant gantry speed and dose rate are feasible without any modifications to the accelerator. Due to the 3 mm‐wide mMLC leaves, the use of a 2 mm calculation grid is recommended. When dual arcs are used for the more complex cases, the overall dosimetric agreement for the SmartArc plans compares favorably with the previously reported results for other implementations of VMAT: γ(3%,3mm) for absolute dose obtained with the biplanar diode array passing rates above 97% with the mean of 98.6%. However, a larger than expected dose error with the single‐arc plans, confined predominantly to the isocenter region, requires further investigationPACS numbers: 87.55Qr, 87.56Nk

Validation of MLC‐based linac radiosurgery for trigeminal neuralgia

Stevens

Lobb

Yenice

2018

This study details a validation process for linear accelerator‐based treatment of trigeminal neuralgia using HD‐MLC field collimation. Nine trigeminal neuralgia treatment plans utilizing HD‐MLC were selected for absolute dose measurement at isocenter using a commercial scintillating detector in an anthropomorphic phantom. Four plans were chosen for film dosimetry measurements in each of the three principal planes to assess spatial dose distribution agreement with the treatment planning system. Additionally, trajectory log analysis for each treatment field in the nine cases was performed to assess mechanical positioning accuracy of the MLC system during delivery. Scintillator and film measurements both revealed mean dose agreement at isocenter of better than 3% while FWHM of the 2D dose distribution in each plane showed agreement between plan and measurement within 0.2 mm. Analysis of log files revealed a maximum MLC leaf positioning error of 0.04 mm across 178 treatment fields. In conjunction with a quality‐controlled treatment delivery methodology, an appropriately commissioned treatment planning system can be used for accurate and clinically appropriate design of trigeminal neuralgia treatment plans utilizing HD‐MLC.