Multi‐level multi‐leaf collimators: Optimization of layer thicknesses and a feasibility study

Abstract

The function of multi-leaf collimators (MLC) is to modulate and shape the intensity of a radiotherapy beam by either blocking or unblocking beamlets. A variation on this functionality is tested in this work wherein the MLC is split into layers, with each layer attenuating the beam by a different amount. In this design, full blocking of a beamlet occurs only if all layers are blocked. This work suggests that such a device, a multi-layer MLC (MLMLC), can deliver dose distributions like a single layer MLC can deliver while requiring less time and monitor units (MU) Methods: Optimal fluences were made for prostate plans using the Eclipse v13.6. An algorithm was developed to create step-and-shoot MLMLC patterns to match these optimal fluences when using up to six layers of MLC. Twelve MLMLC plans were made in total. These patterns were imported back into Eclipse as equivalent tungsten compensators and doses were calculated.Dosevolume histogram (DVH) values,total monitor units (MU),and total time to deliver were compared between arc-style MLMLC plans and nine-field step and shoot IMRT plans created completely in Eclipse using a single layer MLC. Results: When using three or more layers, specified DVH values between the two sets agreed to within 5% while requiring roughly half as much time to deliver and about 20% fewer MU. Conclusions: Demonstrated that having multi-layer MLC can deliver dose distributions like a single layer MLC with less time and monitor units.

Characterization of a novel VenusX orthogonal dual‐layer multileaf collimator

“…34 Multilayer MLCs feature lower dose leakage than single-layer MLCs. 19 The perpendicular placement of the upper and lower MLC layers can reduce intraand interleaf transmissions. According to AAPM TG-50, the average leaf transmission should be <2%, 35 and the average single-layer leaf transmission of the αMLC determined in the present study meets this requirement.…”

“…Current MLCs typically feature a single layer 19 ; however, multilayer MLCs have been gradually introduced to clinical settings 25,27 . Multilayer MLCs offer several important advantages, such as reducing normal organ dose outside the target volume, and requiring less time and fewer monitor units 10,19,28–30 .…”

“…Current MLCs typically feature a single layer 19 ; however, multilayer MLCs have been gradually introduced to clinical settings 25,27 . Multilayer MLCs offer several important advantages, such as reducing normal organ dose outside the target volume, and requiring less time and fewer monitor units 10,19,28–30 . Although dual‐layer micro‐MLC (DmMLC) uses an orthogonal dual‐layer design, there are two main differences between the DmMLC and αMLC.…”

“…Consequently, the stepped boundary of the irradiation field makes it challenging to achieve a smooth target boundary. 18,19 Generally, a good MLC should possess high leaf positioning accuracy, low leaf transmission, small penumbra, and the ability to accurately create various clinically required complex fields. 6,10,17,20 VenusX is a medical linear accelerator (linac) developed by LinaTech (LinaTech LLC, Sunnyvale, CA), a medical company.…”

“…Additionally, the projection width of the traditional single‐layer MLC on the isocenter plane typically ranges from 0.25 to 1.0 cm. Consequently, the stepped boundary of the irradiation field makes it challenging to achieve a smooth target boundary 18,19 . Generally, a good MLC should possess high leaf positioning accuracy, low leaf transmission, small penumbra, and the ability to accurately create various clinically required complex fields 6,10,17,20 …”