Characterization of the Halcyon^TM multileaf collimator system

Abstract

Purpose To characterize the stacked and staggered dual‐layer multileaf collimator (MLC) on the HalcyonTM system. Methods The novel MLC assembly was reviewed and compared to the widely used MillenniumTM 120‐leaf MLC system. We investigated the MLC positioning stability over 70 days using Machine Performance Check (MPC) data. We evaluated the leaf transmission, penumbra, leaf end effect, and leaf edge effect. Leaf transmission through distal, proximal, and both MLC layers was measured with a Farmer chamber, by comparing an open and a closed field. Leaf penumbra was measured using film for three different MLC‐defined field sizes. The leaf end effect was measured with sweeping gap fields of varying gap sizes defined by the distal MLC. The leaf edge effect was evaluated using the Electronic Portal Imaging Device (EPID) for the different banks, gantry positions, and collimator angles. Point dose measurements for 10 test plans were compared to dose predictions of two dose calculation model versions. Results From MPC data, the largest measured MLC positioning accuracy deviation was within 0.1 mm. The proximal MLC exhibited greater deviations compared to the distal MLC. The distal‐and‐proximal‐combination had reduced inter‐leaf and intra‐leaf transmission compared to delivery with distal‐only. The measured leaf transmission was 0.41% for distal‐only, 0.40% for proximal‐only, and negligible for distal‐and‐proximal‐combination. The leaf end penumbra was wider compared to the leaf edge penumbra. The leaf end effect was measured to be −0.2 mm. The leaf edge effect showed minimal bank, gantry position, and collimator angle dependence. However, a systematic deviation between measurements and treatment planning system handling of the leaf edge effect was observed. The discrepancy between the measured and predicted dose in the 10 test plans improved with the latest version of the dose calculation algorithm. Conclusion The characteristics of the stacked and staggered dual‐layer MLC on the HalcyonTM system were presented.

Experience in commissioning the halcyon linac

“…While we did not determine whether this difference was statistically significant or due to the absence of tongue-and-groove from the pre-clinical system, transmission measurements on the clinical Halcyon 1.1 system were within the range specified by Lim et al in their publication describing the characterization of the Halcyon MLC system. 20 Other features of the Halcyon can also be expected to change over time. One key example is the availability of kilo-voltage imaging.…”

Technical Note: Dosimetric characterization of the dynamic beam flattening MLC sequence on a ring shaped, Jawless Linear Accelerator with double stacked MLC

“…The Halcyon linear accelerator is capable of delivering a single 6MV flattening filter free (FFF) beam and utilizes a double stack multi‐leaf collimator (DS‐MLC) system . In prior studies, Lim et al have characterized various aspects of the multi‐leaf collimators on the Halcyon . While the use of the unflattened beam does not pose an obstacle to the delivery of a wide variety of intensity modulated radiotherapy or volumetric modulated arc radiotherapy treatments, it is challenging to create clinically acceptable traditional 3D treatments such as AP/PA spine and 4‐field box without a flat beam without introducing more advanced and lengthy techniques such as field‐in‐field based planning.…”

“…1 In prior studies, Lim et al have characterized various aspects of the multi-leaf collimators on the Halcyon. 2,3 While the use of the unflattened beam does not pose an obstacle to the delivery of a wide variety of intensity modulated radiotherapy or volumetric modulated arc radiotherapy treatments, it is challenging to create clinically acceptable traditional 3D treatments such as AP/PA spine and 4-field box without a flat beam without introducing more advanced and lengthy techniques such as field-in-field based planning. To overcome this problem, a beam flattening sequence was designed for a 6XFFF field which utilized a fixed-MLC sequence to sweep the field and was made available on the Halcyon 2.0.…”

Clinical safety assessment of the Halcyon system

“…There are a number of publications that either evaluate the operation of the Halcyon or provide recommendations on its clinical use . A recent publication provided a risk assessment of Halcyon acceptance testing and commissioning processes using the TG‐100 methodology .…”

“…There are a number of publications that either evaluate the operation of the Halcyon or provide recommendations on its clinical use. [1][2][3][4][5][6][7][8][9][10][11] A recent publication provided a risk assessment of Halcyon acceptance testing and commissioning processes using the TG-100 methodology. 12 In that work, 142 failure modes were identified with the top risk priority number (RPN) values ranging from 85.5 to 95.0 for the acceptance testing and commissioning, respectively.…”