DMLC Motion Tracking Of Moving Targets For Intensity Modulated Arc Therapy Treatment

Main Category: Radiology / Nuclear Medicine
Also Included In: Cancer / Oncology
Article Date: 22 Sep 2008 - 4:00 PDT

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Intensity modulated arc therapy offers great advantages by delivering a fast and highly conformal treatment. However, moving targets represent a major challenge. By monitoring a moving target it is possible to make the beam follow the motion, shaped by a Dynamic MLC (DMLC). The aim of this study was to evaluate the dose delivered to moving targets using the RapidArcTM (Varian Medical Systems, Inc.) technology with and without a DMLC tracking algorithm.

A Varian Clinac iX was equipped with a preclinical RapidArcTMand a 3D DMLC tracking application. A motion platform was placed on the couch, with the detectors on top: a PTW seven29 and a Scandidos Delta4. One lung plan and one prostate plan were delivered. Motion was monitored using a Real-time Position Management (RPM) system. Reference measurements were performed for both plans with both detectors at state (0) "static, no tracking". Comparing measurements were made at state (1) "motion, no tracking" and state (2) "motion, tracking".

Gamma analysis showed a significant improvement for measurements of a moving target with tracking compared to a moving target without tracking compared to the static target measurements: Lung plan; from 87% to 97% pass. Prostate plan; from 81% to 88% pass. Sub-beam information gave a much reduced pattern of periodically spatial deviating dose points for state (2) than for state (1). Iso-dose curve comparisons showed a slightly better agreement between state (0) and state (2) than between state (0) and state (1).

DMLC tracking together with RapidArcTMare a feasible combination, capable of improving the dose distribution delivered to a moving target. It is important to minimise noise influencing the tracking, to gain the full benefit from the application.

Zimmerman Jens et al. Department of Radiation Oncology, Linköping, Sweden

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