MLC tracking for Elekta VMAT: a modelling study

Abstract

A model has been developed to simulate volumetric modulated arc therapy (VMAT) delivery for Elekta control systems. The model was experimentally validated for static-tumour VMAT delivery and has been applied to the investigation of motion compensation with dynamic multileaf collimator (dMLC) delivery tracking for a series of VMAT lung treatment plans at various control point spacings for five patients. The relative increase in treatment time with dMLC tracking was calculated for four 1D rigid-body motion trajectories, and the effect of the control point spacing, the MLC leaf speed and an increased number of dose levels on the dMLC tracking delivery time evaluated. It has been observed that a faster leaf speed is advantageous for motion trajectories with shorter time periods and larger amplitudes. The accuracy of dMLC tracking was found to increase with a decreased control point spacing and is dependent on the amplitude and time period of the motion trajectory of the target. dMLC tracking is shown to be a promising emerging technology which can confer advantage over breath-hold motion-compensation techniques which more drastically reduce the efficiency of VMAT and are more invasive for the patient.

Effects of collimator angle, couch angle, and starting phase on motion‐tracking dynamic conformal arc therapy (4D DCAT)

“…The tracking algorithm was based on the algorithm developed by Sawant et al for motion compensation30 and studies on modifications of beam parameters to generate a linac deliverable plan 31, 33, 34, 35. All machine parameters such as MLC leaf speed, gantry speed, and gantry acceleration were within limits (Table 1) after MLC leaf modification.…”

“…However, in actual delivery, there is a finite time before dose rate reaches the planned value 31, 32, 35. By acquiring delivery parameters (e.g., MLC leaf position errors) of 4D DCAT plans, we could evaluate the discrepancy between plans generated by simulation algorithm and the actual delivered ones.…”

“…Several studies implemented motion tracking with dynamic MLC treatment delivery for either Varian or Elekta linac and reported improved target dose coverage without significantly increasing the total treatment time 30, 31, 32, 33, 34, 35. Sawant et al developed lung tumor motion compensation method where target motion that is decomposed to the beam's eye view (BEV) is dependent on collimator, gantry, and couch angles 30.…”

“…Therefore, optimization of collimator and couch trajectories may reduce the possibility of having plans running at the mechanical limits of the linac, which can improve the treatment efficiency and robustness 36, 37. In most published studies on VMAT plans with motion tracking, collimator, and couch angles for plans were set at 90° and 0°, respectively, which has been shown to be favorable for MLC tracking because the MLC leaf motion direction is parallel to target motion in superior‐inferior (SI) direction 30, 32, 34, 35. However, for (3D) motion tracking, this collimator angle may not be the optimal solution for motion tracking.…”

Planning 4D intensity-modulated arc therapy for tumor tracking with a multileaf collimator

“…Recently, the feasibility of tumor tracking in IMAT delivery is also gaining interest. Davies et al have demonstrated the accuracy and efficiency of tumor tracking in IMAT delivery using a commercial MLC (Davies et al 2011, Davies et al 2013). Considering tracking latency, the effectiveness of MLC tracking for IMAT was also experimentally validated (Bedford et al 2015).…”