Electromagnetic-Guided Dynamic Multileaf Collimator Tracking Enables Motion Management for Intensity-Modulated Arc Therapy

Abstract

Purpose-Intensity modulated arc therapy (IMAT) is attractive due to high dose conformality and efficient delivery. However, managing intrafraction motion is challenging for IMAT. The purpose of this research was to develop and investigate electromagnetic-guided DMLC tracking as an enabling technology to treat moving targets during IMAT.Materials/Methods-A real-time 3D DMLC-based target tracking system was developed and integrated with a linac. The DMLC tracking software inputs a real-time electromagnetically measured target position and the IMAT plan and dynamically creates new leaf positions directed at the moving target. Low and high modulation IMAT plans were created for lung and prostate cancer cases. The IMAT plans were delivered to a 3-axis motion platform programmed with measured patient motion. Dosimetric measurements were acquired by placing an ion chamber array on the moving platform. Measurements were acquired with tracking, without tracking (current clinical practice), and with the phantom in a static position (reference). Analysis of dose distribution differences from the static reference used a γ-test.Results-On average, 1.6% of dose points for the lung plans and 1.2% of points for the prostate plans failed the 3mm/3% γ-test with tracking; without tracking 34% and 14% (respectively) of points failed the γ-test. The delivery time was the same with and without tracking. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Conflict of interest statement:This work was supported by Calypso Medical, the US National Institutes of Health and Varian Medical Systems. This support is acknowledged in the manuscript. There are also co-authors from both Calypso and Varian that have contributed scientifically to this manuscript. NIH Public Access Author ManuscriptInt J Radiat Oncol Biol Phys. Author manuscript; available in PMC 2012 January 1. Conclusions-For the first time electromagnetic-guided DMLC target tracking with IMAT has been investigated. Dose distributions to moving targets with DMLC tracking were significantly superior to those without tracking. There was no loss of treatment efficiency with DMLC tracking.

The impact of leaf width and plan complexity on DMLC tracking of prostate intensity modulated arc therapy

“…This study investigated two of the approaches for improved DMLC tracking accuracy suggested by Keall et al 15 and Poulsen et al:…”

“…4 The traces represented characteristic types of prostate motion: continuous drift, high frequency excursions, persistent excursion, and transient excursion. The traces are the same as in Keall et al 15 The traces started at isocenter. A dosimetric phantom was mounted on the motion platform (Delta4 with Hexamotion, Scandidos, Uppsala, Sweden).…”

“…[2][3][4][5][6][7] Dynamic multileaf collimator (DMLC) tracking is a method to compensate for intrafraction target motion by real-time adaption of the MLC aperture to the targets movement. [8][9][10][11][12][13][14][15][16][17] Other methods of motion compensation, not covered in this study, include beam gating, moving the source, and couch tracking. The accuracy of DMLC tracking depends on the alignment between the leaves and the target motion, with motion perpendicular to the leaf travel being more challenging.…”

The first patient treatment of electromagnetic-guided real time adaptive radiotherapy using MLC tracking for lung SABR

“…The PTV structure was then overlaid to confirm tumour coverage based on beacon localisation. The patient was treated with Calypso-guided MLC tracking [23]. We utilise the kernel density estimation prediction algorithm [24] to account for the system's 220 ms latency [13].…”

First Clinical Implementation of Electromagnetic Transponder-Guided MLC Tracking

“…The investigation of the integration of electromagnetic transponder-guided MLC tracking on a Varian MLC has spanned several domains including geometric accuracy, 7 dosimetric fidelity, 8 quality assurance, 9 compatibility with volumetric modulated arc therapy (VMAT) (Ref. 10) and the ability to correct for in-plane rotation. 11 Note that the current study only corrects for real-time tumor translation and not real-time rotation.…”