Impact of the high-definition multileaf collimator on linear accelerator-based intracranial stereotactic radiosurgery

Abstract

Objectives: The impact of two multileaf collimator (MLC) systems for linear accelerator-based intracranial stereotactic radiosurgery (SRS) was assessed. Methods: 68 lesions formed the basis of this study. 2.5 mm leaf width plans served as reference. Comparative plans, with identical planning parameters, were based on a 5 mm leaf width MLC system. Two collimation strategies, with collimation fixed at 0 u or 90 u and optimised per arc or beam, were also assessed. Dose computation was based on the pencil beam algorithm with allowance for tissue heterogeneity. Plan normalisation was such that 100% of the prescription dose covered 95% of the planning target volume. Plan evaluation was based on target coverage and normal tissue avoidance criteria. Results: The median conformity index difference between the MLC systems ranged between 0.8% and 14.2%; the 2.5 mm MLC exhibited better dose conformation. The median reduction of normal tissue exposed to >100%, >50% and >25% of the prescription dose ranged from 13.4% to 29.7%, favouring the 2.5 mm MLC system. Dose fall-off was steeper for the 2.5 mm MLC system with an overall median absolute difference ranging from 0.4 to 1.2 mm. The use of collimation optimisation resulted in a decrease in differences between the MLC systems. The results demonstrated the dosimetric merit of the 2.5 mm leaf width MLC system over the 5 mm leaf width system, albeit small, for the investigated range of intracranial SRS targets. Conclusion:The clinical significance of these results warrants further investigation to determine whether the observed dosimetric advantages translate into outcome improvements.

Dosimetric comparison of 2.5 mm vs. 3.0 mm leaf width micro-multileaf collimator-based treatment systems for intracranial stereotactic radiosurgery using dynamic conformal arcs: implications for treatment planning

“…4 In December of 2009, the Novalis Tx system (BrainLAB, Varian, Palo Alto, CA, USA), a recently available dedicated platform for image-guided SRS and conventional radiotherapy, was installed in place of the m3 system. [5][6][7][8][9][10][11] This system is equipped with an integrated high-defi nition (HD) mMLC (HD120). [6][7][8][9][10] The m3 mMLC systems, also integrated in the Novalis predecessor system, have a 3 mm leaf width for the central 4.2 cm of the beam, whereas the HD120 mMLC has a 2.5 mm leaf width for the central 8 cm.…”

“…[5][6][7][8][9][10][11] This system is equipped with an integrated high-defi nition (HD) mMLC (HD120). [6][7][8][9][10] The m3 mMLC systems, also integrated in the Novalis predecessor system, have a 3 mm leaf width for the central 4.2 cm of the beam, whereas the HD120 mMLC has a 2.5 mm leaf width for the central 8 cm. 4,5 There is only a 0.5 mm difference in leaf width between the m3 and the HD120.…”

“…1,[8][9][10][12][13][14][15][16][17] The dosimetric advantage for the HD120 mMLC relative to the standard 5 mm leaf width MLC has been reported in terms of dose conformity and normal tissue sparing. [8][9][10] As for the different "micro-"MLCs, Kubo et al compared the threedimensional conformal plans between the 1.7 mm and 3.0 mm leaf width mMLCs, including six brain metastases. 12 They showed only marginal improvement in the 1.7 mm mMLC plans when compared to those from the 3.0 mm mMLC.…”

Dosimetric impact of multileaf collimator leaf width according to sophisticated grade of technique in the IMRT and VMAT planning for pituitary adenoma lesion

“…Generally, IMRT has been considered to be more precise than 3DCRT and DCAT, and the downsizing effect of MLC leaf width is more prominent in 3D-CRT or DCAT than in IMRT [3–6]. Therefore, the sophisticated planning technique may substitute a portion of the downsizing effect of MLC leaf width.…”

Critical neurological structure sparing radiosurgery of vestibular schwannoma: Dosimetric comparison of different techniques and dose prescription methods

“…[17][18][19][20] The recently introduced high definition multi-leaf collimator (HDMLC) in Novalis Tx have demonstrated dosimetric advantage over other MLC in the radiosurgery planning of intracranial tumours. [21] HDMLC together with the capability of modern treatment planning system (TPS) offer various options to choose for. Therefore an appropriate radiation planning and delivery technique should be designed, tested and adopted to reduce the dose to these CNSs while maintaining adequate target coverage.…”