Flipping Book

Dealing with intrafraction motion?

l

Verification images or snapshot verification

during treatment

PHYSICS CONTRIBUTION

TIME DEPENDENCE OF INTRAFRACTION PATIENT MOTION ASSESSED BY

REPEAT STEREOSCOPIC IMAGING

ISCHA

S. H

OOGEMAN

., P

.D., J

OOST

J. N

UYTTENS

, M.D., P

.D., P

ETER

C. L

EVENDAG

, M.D., P

.D.,

AND

J. M. H

EIJMEN

, P

.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.

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

INTRODUCTION

in supine or prone position. Intrafraction motion was as-

sessed by analyzing stereoscopic kV X-ray images acquired

Int. J. Radiation Oncology Biol. Phys., Vol. 70, No. 2, pp. 609–618, 2008

2008 Elsevier Inc.

0360-3016/08/$–see front matter

doi:10.1016/j.ijrobp.2007.08.066

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

Reduction in time = reduction in motion