Design and characterization of a dynamic multileaf collimator

Abstract

The characteristics of a prototype computer-assisted dynamic multileaf collimator (DMLC), specifically designed for small-field conformal radiotherapy, were evaluated at the Istituto Nazionale Tumori of Milan. The collimating device consists of two opposing banks of 16 pairs of 8 cm thick, 3.6 mm wide tungsten leaves and allows shaping of a radiation field up to a size of 10 x 10 cm2 at the isocentre. The screening thickness of each leaf is 6.25 mm at the accelerator gantry isocentre. The leaves have a trapezoidal cross section and move along an arched path, thus providing a 'double focused' collimation system. The DMLC was installed on the head of a Varian Clinac 2100C linear accelerator. Mechanical and dosimetric evaluations were performed to test the stability of the mechanical isocentre and to determine leaf leakage, penumbra width, accuracy of leaf positions and uniformity of leaf speed. Displacement of the mechanical isocentre was less than 1 mm at all gantry angles. Standard radiographic films exposed to 6 MV x-ray radiation were used for dosimetric evaluations. Leakage between leaves was less than 2.5%, and leakage through abutted leaves was less than 5.5%. The penumbra width between 20% and 80% isodose at different positions of leaf banks was 2.7 mm in the direction of the leaf motion and 3.1 mm along the side of the leaf with a standard deviation of 0.2 mm in both directions. Accuracy in the positioning of the leaf was 0.3 mm, whereas the maximum repositioning error was less than 0.2 mm. Finally, during movement of the leaves at the maximum speed of 0.5 mm s(-1), the standard deviation of the leaf positioning error was 0.2 mm, proving an accurate uniformity of leaf speed.

Lung tumor tracking in fluoroscopic video based on optical flow

“…5, [10][11][12][13][14][15][16][17][18][19][20][21][22] Another research effort has been made to shape the radiation beam to synchronously follow the tumor motion using a dynamic multileaf collimator ͑DMLC͒. 12,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Implementation of this method also requires accurate realtime localization of the tumor position during the treatment. Kubo and Hill 13 proposed a method to estimate the tumor position through monitoring an external surface marker.…”

Treatment planning considerations of reshapeable automatic intensity modulator for intensity modulated radiation therapy

“…There are two major groups of commonly used IMRT delivery techniques: collimator-based techniques and physical modulators made of attenuation material. Collimator-based techniques include tomotherapy, 1,2 dynamic multi-leaf collimator ͑DMLC͒, [3][4][5] segmental multi-leaf collimator ͑SMLC͒ 6,7 and intensity modulated arc therapy ͑IMAT͒. 8,9 As compared to multi-leaf collimator-based IMRT techniques, the physical modulators have the major advantage of temporally invariant intensity map delivery, which make it more flexible with monitor unit rate, simpler resolution of interrupted treatment and ease of use with respiratory gating.…”

Commissioning of a double‐focused micro multileaf collimator (μMLC)

“…The leaves have a constant width of 4.7 mm (projected to the isocenter), resulting in a maximum field size of . A study of a prototype of the particular MLC investigated in this paper has been previously published by Loi et al (8) The prototype consisted of only 16 leaf pairs with a constant width of 3.6 mm, making it different from the μMLC used for this study (24 leaf pairs; leaf width varies with distance to center). The leaves move along a curved track so, as the leaves move in and out of the field, the leaf ends are parallel to the beam divergence.…”