IMRT

Dealing with intrafraction motion?

l Verification images or snapshot verification during treatment Int. J. Radiation Oncology Biol. Phys., Vol. 70, No. 2, pp. 609–618, 2008 Copyright ! 2008 Elsevier Inc. Printed in the USA. All rights reserved 0360-3016/08/$–see front matter

doi:10.1016/j.ijrobp.2007.08.066

PHYSICS CONTRIBUTION

TIME DEPENDENCE OF INTRAFRACTION PATIENT MOTION ASSESSED BY REPEAT STEREOSCOPIC IMAGING

M ISCHA S. H OOGEMAN ., P H .D., J OOST J. N UYTTENS , M.D., P H .D., P ETER C. L EVENDAG , M.D., P H .D., AND B EN J. M. H EIJMEN , P H .D.

Department of Radiation Oncology, Erasmus MC - Daniel den Hoed Cancer Center, Rotterdam, The Netherlands

Purpose: To quantify intrafraction patient motion and its time dependence in immobilized intracranial and extra- cranial patients. The data can be used to optimize the intrafraction imaging frequency and consequent patient setup correction with an image guidance and tracking system, and to establish the required safety margins in the absence of such a system. Method andMaterials: The intrafractionmotion of 32 intracranial patients, immobilizedwith a thermoplasticmask, and 11 supine- and 14 prone-treated extracranial spine patients, immobilizedwith a vacuumbag, were analyzed. The motionwas recorded by anX-ray, stereoscopic, image-guidance system. For each group, we calculated separately the systematic (overall mean and SD) and the random displacement as a function of elapsed intrafraction time. Results: The SD of the systematic intrafraction displacements increased linearly over time for all three patient groups. For intracranial-, supine-, and prone-treated patients, the SD increased to 0.8, 1.2, and 2.2 mm, respec- tively, in a period of 15 min. The random displacements for the prone-treated patients were significantly higher than for the other groups, namely 1.6 mm (1 SD), probably caused by respiratory motion. Conclusions: Despite the applied immobilization devices, patients drift away from their initial position during a treatment fraction. These drifts are in general small if compared with conventional treatment margins, but will significantly contribute to the margin for high-precision radiation treatments with treatment times of 15 min or longer. ! 2008 Elsevier Inc. Reduction in time = reduction in motion

Image-guided radiotherapy, Intrafraction motion, Margins, Patient setup, Robotic radiosurgery.

Int. J. Radiation Oncology Biol. Phys. 2008;70(2):609–618

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INTRODUCTION

in supine or prone position. Intrafraction motion was as- sessed by analyzing stereoscopic kV X-ray images acquired