Posters $475

Intake(ml) Group 1 (n-10)

Week 1 2 3 4 5

Median 304 250 214 250 232

I-Q-Range 237 299 379 393 406

Zero intake 2 2 3 3 3

Intake(ml) Group 2 (n-10)

Week 1 2 3 4 5

Median 393 294 110 27 0

I-Q-Range 647 670 375 286 259

Zero intake 2 3 2 4 7

lntake(ml) Group 3 (n-10)

Week 1 2 3 4 5

Median 411 250 179 125 71

I-Q-Range 420 714 616 482 402

Zero intake 0 4 4 5 5

Conclusions: This study has indicated that patients undergoing radical pelvic radiotherapy are not able to consume more than 50% of caloric intake as elemental diet orally and that intake decreases over time. Further study is required to determine whether treatment with this quantity of oral elemental diet has any effect on gastrointestinal toxicity.

1135 poster

Decreasing lung exposure of patients suffering from advanced NSCLC by irradiation in sitting position C. Duisters~ H. Beurskens, M. Starmans, S. Wanders, L. Boersma, T. Verschueren, P. Lambin, A. Minken, D. de Ruysscher

MAASTRO clinic, Radiation Oncology, Maastricht, The Netherlands

Background:After palliative radiotherapy for advanced non- small cell lung cancer (NSCLC), patients often experience radiopneumonitis because large lung volumes are included in the radiation field. A simple method to decrease lung exposure would therefore be welcome. We hypothesized that by irradiating patients in a sitting position, the normal lung volume would become larger and the diameter of the mediastinum smaller, thus resulting in smaller irradiated lung volumes compared to conventional supine position.

Methods: A dedicated chair was constructed in which patients could sit comfortably and reproducibly. A computer program was written to calculate lung volumes from conventional X-rays made during simulation. Lung volumes in supine and in sitting position were compared in patients referred for radiotherapy for locally advanced NSCLC.

Results: In the first 2 patients, the reproducibility of the sitting position was within 1 cm. Moreover, patients preferred the sitting position as well. The irradiated lung volume decreased by 5% in sitting position

Conclusion: On the basis of these first results, irradiating patients with locally advanced NSCLC in a sitting position seems to be feasible. This seems a simple and effective method to decrease lung exposure and hence complications. The study is ongoing and updated results will be presented.

1136 poster

Intracavitary vaginal brachytherapy. A simple planning ?

T. G. Janssen

Arnhems Radiotherapeutisch Instituut, Radiotherapie, Arnhem, The Netherlands

Introduction: Vaginal brachytherapy by use of one central channel cylinder is an easy and widely performed treatment, either adjuvant postoperative or curative for superficial lesions. Standard dose distribution is often used. However if the radiotherapist, for any reason, decides for a homogenic dose distribution it is always preferable to individualize the planning.

Materials and methods: In the Arnhem Radiotherapy Institute intracavitary vaginal brachytherapy is generally performed by a one central channel cylinder, diameter 2; 2.5; 3; 3.5 'or 4 cm, chosen individually to obtain an optimal contact of the applicator surface and the vaginal mucosa. The loaded length depends on a patient's anatomy and/or tumor extension. PDR mSelectron is used, with an Ir 192, 1- 0.5 Ci source, dwell positions each 2.5 mm. The normalization depth is generally at 5 mm from the cylinder surface/vaginal mucosa. The dwell positions and dwell time can be optimized by point dose optimization, laterally parallel to the applicator axis. This results in an inevitable under- or over dosage at the vaginal top. The overdosage depends on the loaded volume and can even exceed 100%. The message given above will be illustrated by various dose distribution examples.

Conclusion: in order to obtain homogeneity of vaginal irradiation, geometric or volume optimization has to be completed by hand optimization.

1137 poster

Incorrect shift prescription due to non-indexing patient position L. van Riien - van Gerwen, N. van de Wiel, M. van Roessel, F. Jacobs

Dr. Bernard Verbeeten Instituut, Radiotherapy, Tilburg, The Netherlands

Patients treated in the pelvic region are positioned in the Dr. Bernard Verbeeten Instituut with a kneerole and an anklefixation which are not indexed. Guided by Ct-images the Virtual Simulator conforms the radiationfields to the target volume. In our procedure we make orthogonal portal images and we match these images on the bony structures. The DRR's and the portal images are compared with each other. The position of the bony structures is important. The portal imager software compares the isocentre 3D and the fieldsizes are just checked if they are correct but have no relevance to the iso check. The software gives us a correctionadvice when the difference is out of the tolerance. For example: Images from a patient show us that there is a shift of the isocentre of 13 mm, but when we look at de fieldedges the difference doesn't seem so big. The portal images and the radiationfields were reconstructed and it seems that due to the deviation of the position of the not- indexed kneerole the pelvis is twisted 3-4 degrees. This is visible on the AP DRR and the LAT DRR. This is due to the wrong patient position. At this moment we are examining whether it is possible to index the kneerole in a simple way without using expensive casts for fixation. SINMED has developed a baseplate that can be attached to the coachtop and on which a kneefix and a feetfix can be placed. The baseplate can be positioned on indexed positions. Now we are testing the use of this baseplate at our institute and we hope that the use of this baseplate will result in a