MotionSim™ Target Motion, Gating & Imaging QA

©JRT Associates 2011

• Assess the interplay effects in MLC based IMRT QA
• Determine the effects of intra-fractional target motion on dose distribution
• Commission and test gating systems
• Commission 4D CT imaging systems
• Qualitative comparison of gated versus non-gated delivery
• Optimization of duty cycles to minimize delivery variations
• Precise reproduction of patient specific and BEV specific 4D-CT respiratory traces
• Integration with all gating surrogate methodologies (markers, pressure belts, etc.)
• Remotely position MapCHECK during the measurement process to increase detector density when desired
• Remotely position MapCHECK for MapCHECK’s precision MLC QA procedure

MotionSim XY/4D works with the MapCHECK / MapCHECK 2 as the only treatment simulator that can reproduce actual target motion (projected to BEV motion for each beam) obtained from a 4D CT (or other methods). The MotionSim XY/4D table incorporates patient 4D-CT tumor trajectories allowing the prescription dose to be delivered to the “in motion” MapCHECK array.

MotionSim XY/4D Workflow


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Use Case 1 Commission a gating system A non-gated delivery is delivered to an in-motion MapCHECK which is driven by a pre-selected motion kernel. A duty cycle is then defined for the gated beam and the same dose is delivered to the in-motion MapCHECK. The nongated delivery should yield a blurry motion with a poor comparison to the TPS, whereas the gated results should be significantly more desirable if the system is functioning correctly.

Use Case 2 Dose QA for moving targets (with gating) Prescription dose to the target (PTV) can be compromised due to the effect of internal target motion. The PTV travels along a motion path which defines the internal target volume (ITV.) MotionSim XY/4D simulates the ITV, so that true dose to the PTV can be assessed. PTV dose may appear to pass with stationary QA, however adding MotionSim XY/4D provides true ITV motion, and the confidence to be sure.

Use Case 3 Access interplay effects in MLC-based IMRT Determining the “interplay effect” in MLC-based IMRT is significant for a given patient plan and target motion. Not taking the interplay effect into consideration during treatment can lead to significant non-uniform fracton-to-fraction dose delivery to the target, further putting the integrity of delivery at risk. The MotionSim XY/4D can be used to assess the interplay effect by comparing gated and non-gated fraction-to-fraction results against the TPS to determine delivery variances.