346 I. J. Radiation Oncology l Biology l Physics Volume 48, Number 3, Supplement. 2000

Results: Measured spine rotational changes were snail, usually only rtO.2-20.4 degrees. Translational motion was greateat in the anterior-posterior (AP) direction, having an amplitudes of approximately I5mm if the subject was lying on a hard table and breathing quietly. Contrastin$y. superior-inferior and lateral movrment~ had amplitude\ of 0.2mm and 0.3mm. respectively. Use of the \tyrofoam bed t-educed AP breathing motion to nn amplitude of O.S-O.Xmm at the thomcic and lumbar spine. There was little effect on the cervical spine motion. With controlled breath-holding. sinusoidal motion in the data disappeared and movement wa‘: typically ?().?~?().4mm. Spine motion was not always minimized by brenth-holding, especially the cervical spine. The sub,ject tended to ~movc from discomfort.

Conclusions: The stereo-optic c;imera system proved to be sensitive and stable. We are encouraged that spinal radiosurgery may be possible if a patient is lying quietly in the prone position. the spine motion is minimized. and the spine is monitored by the camera system. This technique would benelit patient\ who are claustrophobic of a whole body cast. Use of the Styrofoam bed appeared to help reduce breathin g motion within the I mm criterion for radiosurgery. This may allow spinal radiosurgery for a patient, who cannot hold hi&er breath but can lie still and breathe quietly. Additionally. the camera \ystrm could monitor a patient’s motion in conjunctjon with the use of a breath contl-ol device. It could also monitor a patient’s motion during irradiation to warn of large movement\ or gate the radiation beam.

2 166 Development of new head fixation frame and frame mounting system for fractionated stereotactic radiotherapy of brain tumors

Purpose: We Invented the newly developed non-invasive head fixation frame and frame mountin g \gtem using combined techniques of couch mountin g and pedestal mounting \y\tem. In thih paper. we described the details and the relocation accuracy of our \yhtem.

Methods and Materials: Head tixation frame consists of a milled ulluminiurn alloy(duralumin) and is placed to the couch. This frame immobilized patient head using the dental bite, 3.2 mm frontal and occipital thermoplastic mask. The dental bite is tirmly attached to the base frame. To evaluate the coordinate of target isocenter. Brown-Revert-Walls CT locali/rr can be attached to this frame. And also, wc developed the frame mounting system by modit’ying the pedestal mounting system. This system is fixed to couch Roar and can be used to evaluate the isocenteric accuracy of gantry, couch and collimator in QA procedure. In order to measure the relocation accuracy. the acrylic phantom and the accurate pointers have been made. The acrylic phantom contained tive target points in order to confirm stereotactic coordinate. The repovitionin F of the target< in the phantom were estimated by comparing CT coordinates with ECL portal tilma taken with anterior--po~tcriol- and right-left direction.

Results: From analysis of 30 setups ot dltterrnt 5 isocenters in the acrylic phantom urinp ECl. portal tilms. the average distance errors between the target isocrnter and it\ mean position were 0.7 I 5 0. I9 for lateral. 0.15 i 0. I5 for inferior-superior, 0.63 2 0. I8 for anterior-posterior. And the maximum distance error was lesr than 13 ITIIII. Conclusions: The new head tixation ft-ame and fl-ame mounting system were non-in\a\ivtz, accurately relocatable, easy to use and very light. The developed frame mounting syatcm is the moditication of pedestal mounting type. It can be removed. if necessary. after setup procedure by user. The major advantage of using this f~une mounting system i\ complete access to any point in the patient?‘!\ cranium. especially posterior direction.

2167 st ereotactic treatment of extracranial targets: Evaluation of planning target volume (PTV) to compensate for target mobility due to target motion and inaccuracy of patient positioning

U. Haedinger, J. Wulf, LJ. Oppitz. B. Olshausen. W. Thiele, M. Flentje

Univrrsit~ of Wue~-:hurg, Wue,:lxrrg, Grrnrtffl\

Purpose: In extracranial stereotactic radiotherapy high conformal doses are applicated to circumscribed tumor to achieve local control. Efforts are maximired to limit set-up inaccuracy by patient fixation or to incl-ease target reproducibility e.g. by decreasing breathing motions. The main goal is to keep the irradiated volume as small as possible to avoid serious side effects associated with high single doses without decreasing tumor control probability. Reproducibility of the isocenter or target contour in extracranial stereotactic radiotherapy was reported between 2-Smm in three dimensions by different groups. Target mobility in the body might be different in parts of the whole target volume because of the inliuence of adjacent organs or by fixation of parta of the target to mobile structures. Therefore in thi\ study not only target reproducibility at isocenter level but over the whole target volume (gross tumor volume. GTV) was analyzed and the sufticiency of PTV to cover for target mobility over the whole volume wab evaluated.

Materials and Methods: In 2.1 consecutive patients treated in the stereotactic body frame (SBF: ELEKTA Oncol. Syst.) a CT-scan of Smm slices for target simulation was performed prior to irradiation over the whole target volume. The GTV from simulation-CT was matched into the CT-scan for treatment planning without correction of stereotactic coordinate% using the 3Dtrcatmcnt plannine bystem HELAX TMS and detined as new volume of intereat. For matchin, ~1 tiducialh in the SBF sidewalls wcrc chosen as external. independent coordinate system. The decrease of the mean, median and minimum dose to the simulated GTV a\ the lrelevant parameter for target miss were evaluated by dose-volume histograms. PTV and target contouring as the matching procedure were performed by the same physician. Margins for PTV detinition were Smm in axial and IOmm in longitudinal direction. Targeta were localired in the lung (h), liver (4). abdomen (2), pelvis (10). b one (I ). According to the

stereotactic concept dose was normalized to I SO4 with the option to include the PTV by the I OO%isodose.

Results: Standard deviation of planned to simulated GTV-change5 wa\ 9.9cm’ for volumes from 26-457cm’. The median of the minimum dose to the planned GTV was 102%. ranging from 70-127%. It decreased due to target deviation by 27% at median to a median minimal dose of 75% (16-l I X%1. The median and mean dose did not decrease \uh\tantially from 146%