Dosimetric characteristics of dual‐layer multileaf collimation for small‐field and intensity‐modulated radiation therapy applications

Abstract

The purpose of the present work was to measure the performance characteristics in the penumbra region and on the leaf‐end of an innovative dual‐layer micro multileaf collimator (DmMLC). The DmMLC consists of two orthogonal (upper and lower) layers of leaves; a standard MLC consists of one layer. The DmMLC provides unique performance characteristics in smoothing dose undulation, reducing leaf‐end transmission, and reducing MLC field dependence of the leaf stepping angle. Two standard MLCs (80‐leaf and 120‐leaf versions: Varian Medical Systems, Palo Alto, CA), a DmMLC (AccuKnife: Initia Medical Technology, Canton, MA), and a Cerrobend (Cerro Metal Products, Bellefonte, PA) block were used in performance studies involving a triangular field, a cross leaf‐end field, and a circular field. Measurements were made with 6‐MV X‐rays and extended dose range film at a depth of 5 cm in Solid Water (Gammex rmi, Middleton, WI) at a source–axis distance of 100 cm. The field penumbra width measured between the 20% and 80% isodose lines through the MLC‐80, MLC‐120, DmMLC, and Cerrobend block were 9.0, 5.0, 3.0, and 2.0 mm respectively. The dose undulation amplitude of the 50% isodose line was measured as 5.5, 2.0, and 0.5 mm for the MLC‐80, MLC‐120, and DmMLC respectively. The planar dose difference between the MLC‐80, MLC‐120, and DmMLC against Cerrobend block was measured as ranging at ±52.5normal%,±35.0normal%, and ±20.0normal% respectively. The leaf‐end transmission was measured at 22.4% in maximum and 15.4% in average when closing a single layer of the DmMLC, and at 2.4% in maximum and 2.1% in average when closing both layers. The MLC dependence of the leaf stepping angle with the DmMLC ranged from 45 degrees to 90 degrees. The standard MLC leaf stepping angle ranged from 0 degrees to 90 degrees. In conclusion, the dose undulation, leaf‐end transmission, and MLC field dependence of the leaf stepping angle with the DmMLC were remarkably reduced as compared with those of the standard MLCs. And as compared with Cerrobend block, the DmMLC provided very comparable performance in field‐edge smoothing and in the shaping of complex fields.PACS numbers: 87.56.Jk, 87.56.Nk, 87.56.Nj, 87.57.Nt

Delivery of four‐dimensional radiotherapy with TrackBeam for moving target using a dual‐layer MLC: dynamic phantoms study

“…Each leaf of the DmMLC was controlled by a separate motor traveling at maximum speed of 20 mm/sec. The orthogonal layers of the DmMLC reduce MLC field dependence of the leaf stepping angle and provide fast beam response (24) , (25) . Both factors are important in MLC‐based beam tracking.…”

“…In this study, an MLC‐based beam tracking system, TrackBeam (Initia Ltd, Israel) has been assembled and evaluated in our clinic. TrackBeam utilizes a dual‐layer micro MLC (DmMLC) in combination with an online megavoltage (MV) portal imaging device (PID) and a gold fiducial marker implanted inside the tumor (24) , (25) . The MV PID determines the target position in real time by processing the fiducial marker projection (FMP).…”

“…The dual‐layer MLC, offering orthogonal upper and lower banks of leaves, was used to reposition the beam aperture in two dimensions simultaneously. As a result, the dual‐layer MLC provided less angular dependence compared with a standard single‐layer MLC (24) , (25) . An integrated image processing tool (IPT) with an embedded adaptive functionality compensated for the latency of the dynamic beam isocenter and fiducial marker projection.…”

Physical and dosimetric characteristic of high‐definition multileaf collimator (HDMLC) for SRS and IMRT

“…Micro‐MLC (mMLC) having a thinner projected leaf width of about 0.3 cm was introduced either as an add‐on accessory to the existing linac or in‐built in a dedicated linac for application in SRS. ( 6 – 9 ) However, a mMLC suffers from a maximum limited field size of about . A new high‐definition multileaf collimator (HDMLC) having thinner leaf width and yet providing relatively large field size was recently introduced to perform high‐precision radiosurgery and IMRT.…”

An experimental comparison of conventional two-bank and novel four-bank dynamic MLC tracking

“…The AccuLeaf micro multileaf-collimator (mMLC) developed by Azimuth Therapy Ltd features these extra banks, and is used here for the first time to compare conventional MLC tracking of conformal treatment apertures with two MLC banks with MLC tracking with four MLC banks. It has been demonstrated that the four-bank AccuLeaf mMLC offers increased conformality and reduced penumbra for aperture formation (Liu et al 2008), and also that it can confer advantage when sequencing 2D intensity-modulated beams for stepand-shoot intensity-modulated radiotherapy (Webb 2012), but the performance of the AccuLeaf mMLC for dynamic MLC tracking has not previously been investigated.…”