Impact of Multi-leaf Collimator Parameters on Head and Neck Plan Quality and Delivery: A Comparison between Halcyon™ and Truebeam® Treatment Delivery Systems

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Abstract

Purpose

A new dual-layer multi-leaf collimator (MLC) system with several improved characteristics was introduced with the Varian Halcyon™ treatment platform. This study evaluated this new MLC’s impact on head and neck plan quality and delivery efficiency.

Methods

Nine patients were retrospectively studied with Institutional Review Board (IRB) approval. To compare plan quality between the Halcyon dual-layer MLC and Truebeam® MLC, all patients were replanned with the same prescription and target coverage following the institutional clinical protocol for both platforms and using both intensity modulated radiation therapy (IMRT) or volumetrically modulated arc therapy (VMAT) techniques. Organs-at-risk (OAR) dose-volume histogram (DVH) statistics were compared along with total plan monitor units (MU). To evaluate delivery efficiency, actual beam-on time for five patients’ plans were recorded and compared. To evaluate the impact of MLC performance parameters on plan quality, virtual MLC models were generated by matching Truebeam MLC’s parameters to those of the Halcyon dual-layer MLC both individually and combined. OAR doses were then compared between these virtual MLCs, the Truebeam MLC, and the actual Halcyon MLC.

Results

Overall the Halcyon dual-layer MLC provided similar plan quality compared to Truebeam MLC for VMAT plans, and improved sparing for majority of the OARs when using IMRT. Paired comparison showed median dose differences in mean doses to the parotids, cochlea, esophagus, and larynx ranged from -0.83 Gy to 0.37 Gy for VMAT, and from -4.79 Gy to -0.04 Gy for IMRT, with negative values indicating improved performance by Halcyon. Despite a slight increase in plan MU, the Halcyon reduced the total beam-on time by 42.8 ± 8.5%. Virtual MLC simulations demonstrated that matching MLC transmission accounted for nearly half of the total dose difference between Halcyon and Truebeam IMRT plans.

Conclusion

When compared to the Truebeam, the Halcyon’s dual-layer MLC achieved similar plan quality using VMAT, and improved OAR sparing using IMRT, while providing nearly twice as fast treatment delivery. Reduction in MLC transmission is the dominating factor contributing to dosimetric differences in OAR sparing.

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Impact of collimator leaf width and treatment technique on stereotactic radiosurgery and radiotherapy plans for intra- and extracranial lesions

Q. Wu, Zhiheng Wang, John Kirkpatrick … (2009)

Background This study evaluated the dosimetric impact of various treatment techniques as well as collimator leaf width (2.5 vs 5 mm) for three groups of tumors – spine tumors, brain tumors abutting the brainstem, and liver tumors. These lesions often present challenges in maximizing dose to target volumes without exceeding critical organ tolerance. Specifically, this study evaluated the dosimetric benefits of various techniques and collimator leaf sizes as a function of lesion size and shape. Methods Fifteen cases (5 for each site) were studied retrospectively. All lesions either abutted or were an integral part of critical structures (brainstem, liver or spinal cord). For brain and liver lesions, treatment plans using a 3D-conformal static technique (3D), dynamic conformal arcs (DARC) or intensity modulation (IMRT) were designed with a conventional linear accelerator with standard 5 mm leaf width multi-leaf collimator, and a linear accelerator dedicated for radiosurgery and hypofractionated therapy with a 2.5 mm leaf width collimator. For the concave spine lesions, intensity modulation was required to provide adequate conformality; hence, only IMRT plans were evaluated using either the standard or small leaf-width collimators. A total of 70 treatment plans were generated and each plan was individually optimized according to the technique employed. The Generalized Estimating Equation (GEE) was used to separate the impact of treatment technique from the MLC system on plan outcome, and t-tests were performed to evaluate statistical differences in target coverage and organ sparing between plans. Results The lesions ranged in size from 2.6 to 12.5 cc, 17.5 to 153 cc, and 20.9 to 87.7 cc for the brain, liver, and spine groups, respectively. As a group, brain lesions were smaller than spine and liver lesions. While brain and liver lesions were primarily ellipsoidal, spine lesions were more complex in shape, as they were all concave. Therefore, the brain and the liver groups were compared for volume effect, and the liver and spine groups were compared for shape. For the brain and liver groups, both the radiosurgery MLC and the IMRT technique contributed to the dose sparing of organs-at-risk(OARs), as dose in the high-dose regions of these OARs was reduced up to 15%, compared to the non-IMRT techniques employing a 5 mm leaf-width collimator. Also, the dose reduction contributed by the fine leaf-width MLC decreased, as dose savings at all levels diminished from 4 – 11% for the brain group to 1 – 5% for the liver group, as the target structures decreased in volume. The fine leaf-width collimator significantly improved spinal cord sparing, with dose reductions of 14 – 19% in high to middle dose regions, compared to the 5 mm leaf width collimator. Conclusion The fine leaf-width MLC in combination with the IMRT technique can yield dosimetric benefits in radiosurgery and hypofractionated radiotherapy. Treatment of small lesions in cases involving complex target/OAR geometry will especially benefit from use of a fine leaf-width MLC and the use of IMRT.

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Effect of multileaf collimator leaf width on physical dose distributions in the treatment of CNS and head and neck neoplasms with intensity modulated radiation therapy.

H Murshed, Qun J Duan, M A Hyatt … (2002)

The purpose of this work is to examine physical radiation dose differences between two multileaf collimator (MLC) leaf widths (5 and 10 mm) in the treatment of CNS and head and neck neoplasms with intensity modulated radiation therapy (IMRT). Three clinical patients with CNS tumors were planned with two different MLC leaf sizes, 5 and 10 mm, representing Varian-120 and Varian-80 Millennium multileaf collimators, respectively. Two sets of IMRT treatment plans were developed. The goal of the first set was radiation dose conformality in three dimensions. The goal for the second set was organ avoidance of a nearby critical structure while maintaining adequate coverage of the target volume. Treatment planning utilized the CadPlan/Helios system (Varian Medical Systems, Milpitas CA) for dynamic MLC treatment delivery. All beam parameters and optimization (cost function) parameters were identical for the 5 and 10 mm plans. For all cases the number of beams, gantry positions, and table positions were taken from clinically treated three-dimensional conformal radiotherapy plans. Conformality was measured by the ratio of the planning isodose volume to the target volume. Organ avoidance was measured by the volume of the critical structure receiving greater than 90% of the prescription dose (V(90)). For three patients with squamous cell carcinoma of the head and neck (T2-T4 N0-N2c M0) 5 and 10 mm leaf widths were compared for parotid preservation utilizing nine coplanar equally spaced beams delivering a simultaneous integrated boost. Because modest differences in physical dose to the parotid were detected, a NTCP model based upon the clinical parameters of Eisbruch et al. was then used for comparisons. The conformality improved in all three CNS cases for the 5 mm plans compared to the 10 mm plans. For the organ avoidance plans, V(90) also improved in two of the three cases when the 5 mm leaf width was utilized for IMRT treatment delivery. In the third case, both the 5 and 10 mm plans were able to spare the critical structure with none of the structure receiving more than 90% of the prescription dose, but in the moderate dose range, less dose was delivered to the critical structure with the 5 mm plan. For the head and neck cases both the 5 and 10 x 2.5 mm beamlets dMLC sliding window techniques spared the contralateral parotid gland while maintaining target volume coverage. The mean parotid dose was modestly lower with the smaller beamlet size (21.04 Gy v 22.36 Gy). The resulting average NTCP values were 13.72% for 10 mm dMLC and 8.24% for 5 mm dMLC. In conclusion, five mm leaf width results in an improvement in physical dose distribution over 10 mm leaf width that may be clinically relevant in some cases. These differences may be most pronounced for single fraction radiosurgery or in cases where the tolerance of the sensitive organ is less than or close to the target volume prescription.

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Intensity modulated radiation therapy with multileaf collimators of different leaf widths: a comparison of achievable dose distributions.

Uwe Oelfke, Simeon Nill, Marc Münter … (2005)

A planning study to analyze the impact of different leaf widths on the achievable dose distributions with intensity modulated radiation therapy (IMRT). Five patients (3 intra- and 2 extra-cranial) with projected planning target volume (PTV) sizes smaller than 10 cm by 10 cm were re-planned with four different multileaf collimators (MLC). Two internal collimators with an isocentric leaf width of 4 and 10 mm and two add-on collimators with an isocentric leaf width of 2.75 and were evaluated. The inverse treatment planning system KonRad (Siemens Medical Solutions) was used to create IMRT 'step & shoot' plans. For each patient the same arrangement of beams and the same parameters for the optimization were used for all MLCs. The beamlet size for all treatment plans was chosen to coincide with the leaf width of the respective MLC. To evaluate the treatment plans 3D dose distributions and dose volume histograms were analyzed. As indicators for the quality of the PTV dose distribution the minimum dose, maximum dose and the standard deviation were used. For the organs at risk (OAR) the equivalent uniform dose (EUD) was calculated. To measure the dose coverage of the PTV the volume (V(90)) that received doses higher than 90% of the prescribed dose was calculated where for the conformity the dose conformity index given by Baltas et al. was determined. The MLC with the smallest leaf width yields the best mean value of all five patients for the PTV coverage and for the conformity. For the MLCs with the same leaf width, the add-on MLC leads to superior treatment plans than the internal MLC. This is due to the sharper penumbra of the add-on MLC. The number of IMRT field segments to deliver increased by approximately a factor of two if 2. MLC leafs are used instead of the standard 10 mm leafs. In case of the para-spinal patients the EUD value for the spinal cord is only reduced slightly by using MLCs with leaf widths smaller than 5 mm. For the intra-cranial the EUD value for some organs improved with reduced leaf widths while for some organs the 10 mm MLC leafs give comparable values. As expected the MLC with the smallest leaf width always yields the best PTV coverage. Reducing the leaf width from 4 to 2.75 mm results in a slight enhancement of the PTV coverage. With the selected organ parameters no significant improvement for most OAR was found. The disadvantage of the reduction of the leaf width is the increasing number of segments due to the more complex fluence patterns and therefore an increased delivery time.

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Author and article information

Journal

Journal ID (nlm-ta): Cureus

Journal ID (iso-abbrev): Cureus

Journal ID (issn): 2168-8184

Title: Cureus

Publisher: Cureus (Palo Alto (CA) )

ISSN (Electronic): 2168-8184

Publication date (Electronic, pub): 28 November 2018

Publication date (Electronic, collection): November 2018

Volume: 10

Issue: 11

Electronic Location Identifier: e3648

Affiliations

[1 ] Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, USA

Author notes

Taoran Li taoran.li@ 123456uphs.upenn.edu

Article

DOI: 10.7759/cureus.3648

PMC ID: 6351111

PubMed ID: 30723647

SO-VID: d3bb2855-eba4-4424-8287-264e39848ad0

License:

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

History

Date received : 13 November 2018

Date accepted : 27 November 2018

Funding

Research was partially supported by Varian Medical Systems.

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Impact of Multi-leaf Collimator Parameters on Head and Neck Plan Quality and Delivery: A Comparison between Halcyon™ and Truebeam® Treatment Delivery Systems

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Impact of collimator leaf width and treatment technique on stereotactic radiosurgery and radiotherapy plans for intra- and extracranial lesions

Effect of multileaf collimator leaf width on physical dose distributions in the treatment of CNS and head and neck neoplasms with intensity modulated radiation therapy.

Intensity modulated radiation therapy with multileaf collimators of different leaf widths: a comparison of achievable dose distributions.

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